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# User:Txaggiemichael/HotBall

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HotBall is a sport, similar to Table Tennis, in which two players hit a lightweight stress ball back and forth with their hands. The game takes place on a hard "peanut" shaped table divided by a net. Players must allow a ball played toward them only one bounce on their side of the table and must return it so that it bounces on the opposite side. Points are scored when a player fails to return the ball within the rules. Play is fast and demands quick reactions. A skilled player can impart several varieties of spin to the ball, altering its trajectory and limiting an opponent's options to great advantage.

The game was first created in 2007 as an office game by HotSchedules, Inc. in Austin, TX.

## General description

A standard table tennis table, together with a racket and ball

The sport is played with two or four players hitting a ball with rackets back and forth to each other on a table, in a manner similar to tennis. The rules are slightly different, but the concept is very similar. In singles play, the serve is not required to cross from the server's right-hand court to the receiver's right-hand court (or left to left) as it is in tennis. However, serving across is required in doubles play. Ball spin, speed, placement, strategy and tactics play an important part in competitive table tennis matches. The speed of the ball can vary from slow serves with much spin to smashes that travel as fast as 112.5 kilometers per hour (70 mph). [1]

The game is played on a 274 cm × 152.5 cm × 76 cm high (9 ft × 5 ft × 30 inches high) playing surface. The International Table Tennis Federation requires a total playing area not less than 14 m long, 7 m wide and 5 m high for competitions. No limitations in size or shape are specified.

The ball used in table tennis has a diameter of approximately 7 cm, is made of celluloid, and is hollow. A three star rating on a ball usually implies a top quality ball, in relation to its bounce, roundness and their respective consistency between balls of the same make and type.

The winner is the first to score 11 points or more while being ahead by 2 points or more. Players alternate serves every two points. At 10-10 (or deuce) the players alternate with every serve; the winner is then the first person to gain a two point advantage over his opponent. The 11 point game is an International Table Tennis Federation (ITTF) change which occurred in 2001. Previously, the first player to gain 21 points (except in case of a deuce, handled as described above) won the game. All games played at national level and at international tournaments (ITTF) are now played to 11 points in either a best of five (5) games (preliminaries) or best of seven (7) games format (championship matches).

## History

Table tennis depicted on a 1987 postage stamp from the GDR

The game has its origins in England as an after-dinner amusement for upper-class Victorians in the 1880s. Mimicking the game of tennis in an indoor environment, everyday objects were originally enlisted to act as the equipment. A line of books would be the net, a rounded top of a champagne cork or knot of string as the ball, and a cigar box lid as the racket.[2]

Table tennis evolved into the modern game in Europe, the United States and Japan.[3] The popularity of the game led game manufacturers to sell the equipment commercially. Early rackets were often pieces of parchment stretched upon a frame, and the sound generated in play gave the game its first nicknames of "wiff-waff" and "Ping-pong". A number of sources indicate that the game was first brought to the attention of Hamley's of Regent Street under the name "Gossima". The name "ping-pong" was in wide use before English manufacturer J. Jaques & Son Ltd trademarked it in 1901. The name "Ping-Pong" then came to be used for the game played by the rather expensive Jaquesses equipment, with other manufacturers calling theirs table tennis. A similar situation came to exist in the United States where Jaques sold the rights to the "Ping-Pong" name to Parker Brothers.

The next major innovation was by James Gibb,[4] an English enthusiast of table tennis, who discovered novelty celluloid balls on a trip to the U.S. in 1901 and found them to be ideal for the game. This was followed by E. C. Goode who in 1901 invented the modern version of the racket by fixing a sheet of pimpled, or stippled, rubber to the wooden blade. Table tennis was growing in popularity by 1901 when table tennis tournaments were being organized, books on table tennis were being written, and an unofficial world championship was held in 1902. During the early 20th century the game was banned in Russia due to a belief that was held by the rulers at the time that playing the game had an adverse effect on players' eyesight. In 1921, the Table Tennis Association was founded in England, and the International Table Tennis Federation followed in 1926. London hosted the first official world championship in 1927. Table tennis was introduced as an Olympic sport at the Olympics in 1988.

In the 1950s rackets that used a rubber sheet combined with an underlying sponge layer changed the game dramatically, introducing greater spin and speed. These were introduced to England by the sports goods manufacturers S.W. Hancock Ltd. The use of speed glue increased the spin and speed even further, resulting in changes to the equipment to "slow the game down".

Toward the end of 2000, the ITTF instituted several rules changes aimed at making table tennis more viable as a televised spectator sport. First, the older 38 mm (1.5 inch) balls were officially replaced by 40 mm balls. This increased the ball's air resistance and effectively slowed down the game. By that time, players had begun increasing the thickness of the fast sponge layer on their rackets, which made the game excessively fast, and difficult to watch on television. Secondly, the ITTF changed from a 21 to an 11-point scoring system. This was intended to make games more fast-paced and exciting. The ITTF also changed the rules on service to prevent a player from hiding the ball during service, in order to increase the average length of rallies and to reduce the server's advantage. Variants of the sport have emerged. "Large-ball" table tennis uses a 44 mm ball which slows down the game significantly. This has seen some acceptance by players who have a hard time with the extreme spins and speeds of the 40 mm game. The ball's mass is 2.47 grams.

There is a move towards reviving the table tennis game that existed prior to the introduction of sponge rubber. Classic table tennis like Liha[5] or "hardbat" table tennis players reject the speed and spin of reversed sponge rubber, preferring the 1940–60s play style, with no-sponge, short-pimpled rubber equipment, when defense is less difficult by decreasing the speed and eliminating any meaningful magnus effect of spin. Because hardbat killer shots are almost impossible to hit against a skilled player, hardbat matches focus on the strategic side of table tennis, requiring skillful maneuvering of the opponent before an attack can be successful.

## Equipment

### Ball

The international rules specify that the game is played with a light 2.7 gram, 40 mm diameter ball. Generally, it is the most-used ball. The rules say that the ball shall bounce up 23 cm when dropped from a height of 30 cm thereby having a coefficient of restitution of 0.88. The 40 mm ball was introduced after the 2000 Olympic Games. However, this created some controversy as the Chinese National Team argued that this was merely to give non-Chinese players a better chance of winning[citation needed]. A 40 mm table tennis ball is slower and spins less than a 38 mm one. The ball is made of a high-bouncing gas-filled celluloid, colored white or orange, with a matte finish. The choice of ball color is made according to the table color and its surroundings. For example, a white ball is easier to see on a green or blue table than it is on a grey table. Stars on the ball indicate the quality of the ball. 3 stars indicates that it is of the highest quality, and is used in official competitions.

• The volume is ${\displaystyle {\frac {32000\pi }{3}}}$ mm cubed.
• The Surface area is ${\displaystyle 1600\pi }$ mm squared.
• The perimeter is ${\displaystyle 40\pi }$ mm.

### Table

Diagram of a table tennis table showing the official dimensions

The table is 2.74 m (9 ft) long, 1.525 m (5 ft) wide, and 76 cm (30 inch) high with a Masonite (a type of hardboard) or similarly manufactured timber, layered with a smooth, low-friction coating. The table or playing surface is divided into two halves by a 15.25 cm (6 inch) high net.[6] The table surface is often in a green or blue color.

### Racket

Players are equipped with a laminated wooden racket covered with rubber on one or two sides depending on the grip of the player. This is called either a paddle, racket, blade or a bat depending on where in the world the game is being played. In the USA the term "paddle" is common, in Europe the term is "bat," and the official ITTF term is "racket."

Table tennis regulations allow different surfaces on each side of the racket. The different types of surfaces provide various levels of spin or speed, or in some cases, nullify spin. For example, a player may have a rubber that provides much spin on one side of his racket, and no spin on the other side of the racket. By flipping the racket in play, different types of returns are possible. To help a player distinguish between different types of rubber used by his opposing player, international rules specify that one side must be red while the other side must be black. The player has the right to inspect his opponent's racket before a match to see the type of rubber used and what color it is. Despite high speed play and rapid exchanges, a player can see clearly what side of the racket was used to hit the ball. Current rules state that, unless damaged in play, the racket cannot be exchanged for another racket at any time during a match.

## Game play

### Starting a game

In top-flight competition, service is decided by a coin toss. At lower levels it is common for one player (or the umpire/scorer) to hide the ball in one or the other hand (usually hidden under the table), allowing the other player to guess which hand the ball is in. The correct or incorrect guess gives the "winner" the option to choose to serve, receive, or to choose which side of the table to use. Another method is for one player to hit the ball to the other and he or she returns it or by hitting it back and forth four times and then playing out the point. This is commonly referred to as "play to serve". Then, they play one point to see who serves first. Players also determine the first to serve by placing a racket on the table with the handle off the board, taking turns throwing the ball at their opponent's racket. The first to strike the opponent's racket without receiving a return shot gets the serve.

### Service

In game play, the player serving the ball commences a point. Standing so that the ball is held behind the endline of the table, with the ball in the palm of the free hand—over the table's height—and the racket in the other, the server tosses the ball without spin, upward, at least 16 centimeters (approximately 6 inches). In casual (non-tournament) games, many players do not toss the ball upward, however this is technically illegal and can give the serving player an unfair advantage. The ball must remain above the height of the table at all times. The server cannot use his body or clothing to obstruct sight of the ball; the opponent and the umpire must have a clear view of the ball at all times

He or she then must hit the ball from behind the baseline such that it bounces once on his or her half of the table, and then bounces at least one time on the opponent's half. If the ball strikes the net but does not strike the opponent's half of the table, then a point is awarded to the opponent. However, if the ball hits the net, but nevertheless goes over and bounces on the other side, it is called a let (or net-in). Play stops, and the ball must be served again with no penalty. A player may commit any number of lets without penalty.

If the service is "good", then the opponent must then make a "good" return—by returning the ball before it bounces on his or her side of the table a second time. Returning the serve is one of the most difficult parts of the game, as the server's first move is often the least predictable—due to the numerous spin choices at his or her disposal—and thus most advantageous to him or her.

### Hitting the ball

Any hitting of the ball must be done such that the ball passes over or around the net. If the ball is struck such that it travels around the net, but still lands on the opponent's side of the table, the hit is legal and play should be continued. If a player cannot return a legal hit over (or around) the net so that the ball bounces on the opposite side of the table, the player loses the point.

### Scoring

Points are awarded to the opponent for any of several errors in play:[7]

• Allowing the ball to bounce on one's own side more than once.
• Double hitting the ball. Note that the hand below the wrist is considered part of the racket and making a good return off one's hand or fingers on the racket-holding hand is allowed, but hitting one's hand or fingers and subsequently hitting the racket is a double strike and an error.
• Allowing the ball to strike anything other than the racket (see above for definition of the racket)
• Causing the ball not to bounce on the opponent's half (i.e., not making a "good" return)
• Placing one's free hand on the playing surface or moving the playing surface
• Offering and failing to make a good serve (i.e., making a service toss and failing to strike the ball fairly into play)
• Making an illegal serve: (e.g., one preceded by a player's hiding the ball or his failing to toss the ball at least 16 centimeters (six inches) in the air).
• Hitting the net with racket or any body part.
• By volleying the ball (not allowing the ball to bounce on your side)
• The ball is considered out of bounds if: It touches a wall, ceiling, the opponent's body, or is stopped by the opponents racket.

### Alternation of service

Service alternates between opponents every two points (regardless of winner of the rally) until a player reaches 11 points with at least a two-point lead, or until both players have 10 points a piece. If both players reach 10 points, then service alternates after each point, until one player gains a two-point advantage. This is the currently used standard followed by the ITTF.[8]

In doubles, service alternates every two points between sides, but also rotates between players on the same team. At the end of every two points, the receiving player becomes the server, and the partner of the serving player becomes the receiver.

In the 21-point game system, service would alternate every 5 points. If both players reached a score of 20, then service would alternate each point until one player gains a two-point advantage.

### Series of games

After each game, players switch sides of the table and in the fifth or seventh, game "for the match", players switch sides when the first player scores 5 points, regardless of whose turn it is to serve. In competition play, matches are typically best of five or seven games.

### Doubles game

Service zone in doubles game

In addition to games between individual players, pairs may also play table tennis. In doubles, all the rules of single play apply except for the following. A line painted along the long axis of the table to create doubles courts bisects the table. This line's only purpose is to facilitate the doubles service rule, which is that service, must originate from the right hand "box" in such a way that the first bounce of the serve bounces once in said right hand box and then must bounce at least once in the opponent side's right hand box (far left box for server). Play then continues normally with the exception that players must alternate hitting the ball. For example, after a player serves, the receiving player makes his or her return, the server's partner returns the ball and then the service receiver's partner would play the ball. The point proceeds this way until one side fails to make a legal return and the point is then awarded to the other team. Also, when the game reaches the final set, the teams must switch side and the team that receives the service must switch receiver when one of the teams reach 5 points. Singles and doubles are both played in international competition, including the Olympic Games since 1988 and the Commonwealth Games since 2002. In 2005, the ITTF announced that doubles table tennis will only be featured as a part of teams events in the 2008 Olympics.

## Styles of play

### Grip

Competitive table tennis players grip their rackets in a variety of ways. The manner in which competitive players grip their rackets can be classified into two major families of styles. One is described as penhold, and the other shakehand. The Laws of Table Tennis do not prescribe the manner in which one must grip the racket, and numerous variations on gripping styles exist.

Penhold
The penhold grip is so-named because one grips the racket similarly to the way one holds a writing instrument. The style of play among penhold players can vary greatly from player to player. The most popular style, usually referred to as the Chinese penhold style, involves curling the middle, ring, and fourth finger on the back of the blade. The amount of curl in the fingers can vary from clenched, to almost perfectly straight. The three fingers however, will always remain touching one another. Chinese penholders favour a round racket head, for a more over-the-table style of play. In contrast, another style, sometimes referred to as the Japanese penhold grip, involves splaying those three fingers out across the back of the racket, usually with all three fingers touching the back of the racket, rather than stacked upon one another. Japanese penholders will often use a square-headed racket for an away-from-the-table style of play. Traditionally these square-headed rackets feature a block of cork on top of the handle, as well as a thin layer of cork on the back of the racket, for increased grip and comfort. Penhold styles are popular among players originating from East Asian regions such as China, Taiwan, Japan, and South Korea.
Traditionally, penhold players use only one side of the racket to hit the ball during normal play. The side which is in contact with the last three fingers is generally not used. However, the Chinese have developed a new technique in which a penholder utilizes both sides of the racket. This is referred to as the Reverse penhold backhand (RPB) where the player produces a stroke (most often topspin) by turning the traditional side of the racket to face him or herself, and swinging, with a backhand motion, using the opposite side of the racket. This stroke has greatly improved and strengthened the penhold style both physically and psychologically, as it eliminates the strategical weakness of the traditional penhold backhand.
Shakehand
The shakehand grip is so-named because one grips the racket similarly to the way one performs a handshake. The grip is sometimes colloquially referred to as a "tennis grip" or a "Western grip," although it has no correlation to the Western grip used in Tennis. The shakehand grip is most popular among players originating in Western nations and South Asian nations, for example. Today, though, there are many Asian players using the shakehand grip[citation needed]. This is due to the increasingly fast nature of the game, making the backhand stroke more prevalent, a stroke which is difficult to execute consistently at a high standard when using the penhold grip.

### Types of shots

The strokes break down into generally offensive and defensive. The types of strokes include backhand and forehand. The shots vary from the forehand loop to the backhand smash.

#### Offensive strokes

Speed drive
These strokes differ to ones from other racket sports like tennis. The racket is primarily perpendicular to the direction of the stroke, and most of the energy applied to the ball results in speed rather than spin, creating a shot that does not arc much, but is fast enough that it can be difficult to return. A speed drive is used mostly for keeping the ball in play, applying pressure on the opponent and potentially opening up an opportunity for a more powerful attack.
Loop drive
Essentially the reverse of the speed drive. The racket is much more parallel to the direction of the stroke ("closed") and the racket thus grazes the ball, resulting in a large amount of topspin. A good loop drive will arc quite a bit, and once striking the opponent's side of the table will jump forward, much like a kick serve in tennis. Returning a loop drive may not be as difficult to return as a speed drive; however, because of its topspin, it is more likely to rebound off the opponent's racket at a very high angle, setting up an easy smash (described below) on the follow up. As the loop drive requires a lot of topspin, players generally use their entire body to generate the movement required. Variations in spin and speed add to the effectiveness of this shot.
Chinese players categorize loop-drives in 3 variations based on trajectories:
1. The "Loop"
The "Loop" produces a more pronounced loopy arc, with a higher trajectory and extreme topspin, but is typically slower.
2. The "Loop Kill" ("Rush" in China)
The "Loop Kill" produces a flatter arc, with higher speed that resembles a speed drive but with stronger topspin, typically used for replacing speed drive or smash in "put-away" situations.
3. The "Hook"
Similar to a regular Loop, but carries a tilted topspin (or is referred as the "top-side" spin), it bounces sideways and downward upon hitting the table. Similar to but stronger than the defensive "side-drive" described below.
Counter drive
Usually a counter attack against drives (normally high loop drives). You have to close the racket and stay close to the ball (try to predict its path). The racket is held closed and near to the ball, which is hit with a short movement "off the bounce" (before reaching the highest point) so that the ball travels faster to the other side. If performed correctly, a well-timed, accurate counter-drive can be as effective as a smash.
Flip (or Flick in Europe
When a player tries to attack a ball that has not bounced beyond the edge of the table, he/she does not have the room to wind up in a backswing. The ball may still be attacked, however, and the resulting shot is called flip because the backswing is compressed into a quick wrist action. A flip is not a single stroke and can resemble either a drive or a loop in its characteristics. What identifies the stroke is instead whether the backswing is compressed into a short wrist flick. Also known as 払い "harai" in Japanese.
Smash
The offensive trump card in table tennis. A player will typically execute a smash when his or her opponent has returned a ball that bounces too high and/or too close to the net. Smashing is essentially self-explanatory—large backswing and rapid acceleration imparting as much speed on the ball as possible. The goal of a smash is to get the ball to move so quickly that the opponent simply cannot return it. Because the ball speed is the main aim of this shot, often the spin on the ball is something other than topspin. Sidespin can be used effectively with a smash to alter the ball's trajectory significantly, although most intermediate players will smash the ball with little or no spin. An offensive table-tennis player will think of a rally as a build-up to a winning smash; only a calculated series of smashes can guarantee a point against a good opponent. However, most players will be able to return at most one or two smashes consistently. Provided that the opponent is not too close to the table or too far away from the ball, a smash can be lobbed, chopped, blocked or even counter-looped, albeit with some difficulty. A player who smashes generally works out a series of smashes (and possibly drop-shots) to rush the opponent out of position, put him off balance, or both. Smashers who fail to do this find it difficult to win a point against an excellent defense.

#### Defensive strokes

Push (or Slice in Asia)
The push is usually used for keeping the point alive and creating offensive opportunities. A push resembles a tennis slice: the racket cuts underneath the ball, imparting backspin and causing the ball to float slowly to the other side of the table. While not obvious, a push can be difficult to attack because the backspin on the ball causes it to drop toward the table upon striking the opponent's racket. In order to attack a push, a player must usually loop the ball back over the net. Often, the best option for beginners is to simply push the ball back again, resulting in pushing rallies. For good players it may be the worst option because the opponent will counter with a loop, putting you in a defensive position from which most likely you will lose, unless you are a good chopper. Another option to pushing is to flip the ball when it is close to the net. Pushing can have advantages in some circumstances. Players should only push when their opponent makes easy mistakes. Offensive players should only push for variation and not for general rallies. A push can easily be counter-looped into the opposite corner if it is not short enough. The goal of most player's pushes is to make the ball land too short to be attacked, rather than attempting to over-spin the opponent.
Chop
A chop or cut is the defensive, backspin counterpart to the offensive loop drive. A chop is essentially a bigger, heavier slice, taken well back from the table. The racket face points primarily horizontally, perhaps a little bit upward, and the direction of the stroke is straight down. The object of a defensive chop is to match the topspin of the opponent's shot with your own backspin. A good chop will float nearly horizontally back to the table, in some cases having so much backspin that the ball actually rises. A chop such as this can be extremely difficult to return due to the enormous amount of backspin. Sometimes a defensive player can impart no spin on the ball during a chop, or frequently add right- or left-hand spin to the ball. This may further confuse his/her opponent. Chops are difficult to execute, but are devastating when completed properly because it takes a tremendous amount of topspin on a loop drive to return the ball back over the net.
Block
The block or short is a simple shot, barely worthy of being called a "stroke," but nonetheless can be devastating against an attacking opponent. A block is executed by simply putting the racket in front of the ball—the ball rebounds back toward the opponent with nearly as much energy as it came in with. This is not as easy as it sounds, because the ball's spin, speed, and location all influence the correct angle of a block. It is very possible for an opponent to execute a perfect loop, drive, or smash, only to have the blocked shot come back at him just as fast. Due to the power involved in offensive strokes, often an opponent simply cannot recover quickly enough, and will be unable to return his own shot blocked back to him/her. Blocks almost always produce the same spin as was received, which is nearly always topspin.
Push-Block
High level players may use what is called push block or active block, adding speed to the ball (with a small topspin movement). When playing in the Penhold Grip, many players use push blocks when being pressured on the backhand. Chinese pen-hold players refer to it as a push-block as they literally "push" their backhand forward, instead of simply blocking it.
Kill spin
Kill spin is a new shot that is played only when the ball bounces low just on the other side of the net. To play the shot you must stand at the side of the table and open your bat angle and bend your arm then you as lightly and as softly as possible just touch the ball over the net and bring your bat back slightly this creates a lot of back spin in an extremely light shot which results in the ball just trickling over the net and bounces many times making it almost impossible for your opponent to hit it back.
Side Drive
This spin shot is alternately used as a defensive and offensive maneuver. The premise of this move is to put a spin on the ball either to the right or the left of the racket. The execution of this move is similar to a slice, but to the right or left instead of down. This spin will result in the ball curving to the side but bouncing in the opposite direction when the opponent returns it. Do not attempt a right-side spin (moving your arm to the right when hitting the ball) when too close to the left side of the table, and vice versa. To return, simply execute the same sided spin as your opponent just gave you.
Lob
The defensive High Ball or Lob is possibly the visually most impressive shot in the sport of table tennis, and it is deceptive in its simplicity. To execute a High Ball, a defensive player first backs off the table 4-6 meters; then, the stroke itself consists of simply lifting the ball to an enormous height before it falls back to the opponent's side of the table. A High Ball is inherently a creative shot, and can have nearly any kind of spin you can imagine. Top quality players use this fact to their advantage in order to control the spin of the ball. For instance, though the opponent may smash the ball hard and fast, a good defensive Lob could be more difficult to return due to the unpredictability (and heavy amounts) of the spin on the ball. Thus, though backed off the table by tens of feet and apparently running and leaping just to reach the ball, a good defensive player can still win the point using good High Balls. However, most of the time one will lose the point so it is not recommended unless it is really necessary.
Drop Shot
The drop shot is a high level stroke, used as another variation for close-to-table strokes (like harai and slice). You have to position the racket close to the ball and just let the ball touch it (without any hand movement) in a way that the ball stays close to the net with almost no speed and spin and touches the other side of the table more than twice if the opponent doesn't reach it. This stroke should be used when opponents are far from the table and not prepared to get close to the table. This technique is most usually done by pen-holders and players who use long or short pimples. A very deceiving technique, this could result in the opponent failing to reach the ball after misjudging the distance of the ball. A perfectly executed stroke after a topspin sequence can win a point.

## Effects of spin

Adding spin onto the ball causes a whole range of major and minor changes:

4 phases in a backspin curve

Backspin: The easy-to-learn backspin strokes adds subtle lift to the first part of the ball-curve, lets the ball drop more suddenly, makes the ball bounce more upright and most significantly: makes the ball dive downwards when the opponent uses a common rubber (pimples inwards) on his racket. (The opponent is forced to seriously compensate for the backspin) Due to the initial lift of the backspin-curve, there’s a limit on how much speed one can hit the ball without overflying the opponents half. Backspin also makes it harder for the opponent to hit the ball with lots of speed. In table-tennis backspin is regarded as a defensive alternative, due to: the limitation on ballspeed, the simplicity of producing the strokes and the daring of the opponent. (It is possible to smash with backspin offensively, but only on easy high balls, close to the net)

4 phases in a topspin curve

Topspin: The hard-to-learn topspin strokes has a minor influence on the first part of the ball-curve, but the Magnus effect clearly forces the ball back down as it approaches the opposing side. On the bounce the topspin will accelerate the ball a little more. Again the most significant change appears when the opponent hits the ball (with a common pimples inwards rubber on his racket). Due to the topspin the ball jumps upwards and the opponent is forced to seriously compensate for the topspin. There’s virtually no limit on how much speed a topspin-ball can be given (besides your own timing and strength) and a speedy topspin stroke gives the opponent very little time to respond. In tabletennis topspin is regarded as a offensive alternative, due to: the virtual limitless ballspeeds, the highly required skills for producing the strokes and the enhanced tactical pressure on the opponent. (It is possible to play defensive topspin-lobs from far behind the table, but only world class players use this type of gallery play successfully)

## Competition

Competitive table tennis is popular in Asia and Europe and has been gaining attention in the United States. The most important international competitions are World Cup, World Championship, the Olympics and the ITTF Pro Tour, as well as continental competitions like European Championship, Euro Top-12, Asian Championship and Asian Games. China continues to dominate most world titles, while other strong teams come from East Asia and Europe including France, Germany, former Yugoslavia, Hong Kong, Japan, South Korea, Singapore, Sweden, and Taiwan.

There are also professional competitions at the clubs level. The national league of countries like China (the China Table Tennis Super League), Germany, France, Belgium and Austria are some of the examples being at the highest level. There are also some important international club teams competitions such as the European Champions League and its former competition, the European Club Cup, which the top club teams from different European countries compete.

#### Chinese Dominance

A Chinese player has won the men's World Championship 60% of the time since 1959; in the women's competition, a Chinese player has won all but two of the World Championships since 1971.

## Notable players

An international hall of fame exists at the "ITTF Museum webpage" (PDF). (349 KB). A Grand Slam is earned by a player who wins an Olympic Games gold medal, world championship title, and World Cup of Table Tennis gold medal.

## Governance

The International Table Tennis Federation (ITTF): worldwide governing body with national bodies responsible for the sport in each country. There are other local authorities applicable as well.

• The European Table Tennis Union is the governing body responsible for table tennis in Europe.
• The English Table Tennis Association is the governing body responsible for table tennis in England.
• The Irish Table Tennis Association is the governing body responsible for table tennis in Ireland.
• The Scottish Table Tennis Association is the governing body responsible for table tennis in Scotland.
• The Table Tennis Association of Wales is the governing body responsible for table tennis in Wales.
• The Canadian Table Tennis Association is the governing body responsible for table tennis in Canada.
• The USA Table Tennis (USATT): national governing body for table tennis in the United States.
• The National Collegiate Table Tennis Association (NCTTA): official governing body for collegiate table tennis in the United States.

## Miscellaneous

• Multi-talented sportsman Max Woosnam, an Olympic and Wimbledon champion at lawn tennis and one-time captain of the England national football team, once defeated actor and film director Charlie Chaplin at table tennis while playing with a butter knife instead of a racket.[9]
• Table tennis inspired the first commercially successful video game, Pong.
• In the early 1970s the People's Republic of China (PRC) invited American table tennis players to a tournament in the PRC. This marked a thawing in relations with the United States that was followed up by a visit by U.S. president Richard Nixon. The popular media therefore dubbed this visit "Ping Pong Diplomacy".
• At the 1936 World Championships contested in Prague, two defensive players took over an hour to contest one point. The entire match lasted over four hours.
• More than 30 table tennis companies exist around the world, making a full line of accessories from rackets to warm-up suits.[citation needed]
• A man in Hawaii has invented a three-player table for table tennis, calling it Tri-Pong.
• There are also competitions in table tennis variants: "Hardbat", in which all competitors use a racket with small pips-out rubber (sponge is not allowed); and "Large ball", where a 44 mm ball is used to decrease the speed.
• Comedian George Carlin once noted in a stand-up routine that all racquet sports are derivatives of Ping Pong: for instance, tennis is "Ping Pong played while standing on the table," and even volleyball is "racquetless, team Ping Pong played with a raised net and an inflated ball while standing on the table."

## Notes

1. ^ "Speed of ball article from the International Table Tennis Federation". Ittf.com. Retrieved 2009-07-30.
2. ^ Did You Know? "Westside News", April 9, 2008, published in Brisbane, Queensland, Australia
3. ^ "History of table tennis from the Table Tennis Museum of the International Table Tennis Federation". Ittf.com. Retrieved 2009-07-30.
4. ^ "University of Florida table tennis history project". Iml.jou.ufl.edu. 1971-04-06. Retrieved 2009-07-30.
5. ^ Harry (2009-05-16). "Untold Story of Liha/Sandpaper Racket of Table Tennis in the Philippines". Tatapx.org. Retrieved 2009-07-30.
6. ^ "Table tennis ball regulations at". Sizes.com. 2000-10-01. Retrieved 2009-07-30.
7. ^ "The Laws of Table Tennis" (PDF). (28.0 KB) at the ITTF. Retrieved July 2007.
8. ^ http://www.ittf.com/ittf_handbook/2008/2.pdf
9. ^ Collins, Mick (2006). All-Round Genius: The Unknown Story of Britain's Greatest Sportsman. London: Aurum Press Limited. ISBN 1-84513-137-1.


text:
# KCET 2017 Physics Paper with Solutions

KCET 2017 Paper with Solutions Physics is available here. Revise them and gain confidence, which in turn reduces the fear of facing the examination. It will help the students to attempt maximum questions in stipulated time by increasing their speed and accuracy. Candidates can download the previous years’ question papers of KCET to figure out the alternative and easy method to solve a particular problem. Practising the previous year papers is the best tool for the preparation of this competitive exam KCET, in terms of the syllabus and distribution of marks across different topics. Solving these papers with solutions will boost the candidates’ confidence and scores in the KCET examination.

### KCET 2017 - Physics

Question 1: A substance of mass 49.53 g occupies 1.5 cm3 of volume. The density of the substance (in g cm3) with the correct number of significant figures is

1. a. 3.302
2. b. 3.300
3. c. 3.3
4. d. 3.30

Solution:

Bonus

Question 2: A car moving with a velocity of 20 ms–1 is stopped in a distance of 40 m. If the same car is travelling at double the velocity, the distance travelled by it for the same retardation is

1. a. 640 m
2. b. 320 m
3. c. 1280 m
4. d. 160 m

Solution:

Let the initial speed of car be u = 20 m / s

Final speed of car; V = 0 m / s

Retardation = a

Case – I

V2 = u2 + 2as

0 = u2 + 2as

– 400 / [2 * 40] = a

[a = –5 m / s2]

Case – II

u = 40 m / s

v = 0 m / s

a = –5 m / s2

s = ?

V2 = u2 +2as

0 = (40)2 + 2 (–5). S

S = 1600 / 10

S = 160 m

Question 3: The angle between velocity and acceleration of a particle describing uniform circular motion is

1. a. 45º
2. b. 60º
3. c. 90º
4. d. 180º

Solution:

In a circular motion, velocity is always tangential to the circular path. Also in a uniform circular motion, tangential acceleration is zero. Hence, the net acceleration will be centripetal acceleration which always acts towards the centre of the circular path. Hence, velocity and acceleration of a particle describing uniform circular motion are at a right angle to each other.

Question 4: If $\vec{A} = 2 \hat i + 3 \hat j + 8 \hat k$ is perpendicular to $\vec{B} = 4 \hat j - 4 \hat i + \alpha \hat k$ then the value of ‘α’ is

1. a. 1 / 2
2. b. -1 / 2
3. c. 1
4. d. –1

Solution:

When vectors are perpendicular to each other, then their dot product is zero.

$\vec{A} . \vec{B}$ = 0

$(2 \hat i + 3 \hat j + 8 \hat k) . (4 \hat j - 4 \hat i + \alpha \hat k)$ = 0

–8 + 12 + 8α = 0

8α = - 4

α = - 1 / 2

Question 5: A body of mass 50 kg, is suspended using a spring balance inside a lift at rest. If the lift starts falling freely, the reading of the spring balance is

1. a. = 50 kg
2. b. > 50 kg
3. c. < 50 kg
4. d. = 0

Solution:

As the lift is falling freely, therefore its acceleration = g (downwards)

Let, the force acting on body due to spring is “F”

∴ (50g) – F = (50) a

50g – F = 50 g

F = 0

Thus, no force is acting on the body due to spring.

So, the reading of spring balance is zero.

Question 6: A motor pump lifts 6 tones of water from a well of depth 25m to the first floor of height 35 m from the ground floor in 20 minutes. The power of the pump (in kW) is [g = 10 ms–2]

1. a. 3
2. b. 6
3. c. 1.5
4. d. 12

Solution:

Power = work done / time taken

P = mgh / t

P = (m / t) gh

h = 25 + 35 = 60m

Flow rate = (m / t) = 6 tones / 20 min

= {[6000] / [20 * 60]} (kg / sec) = 5 (kg / sec)

P = 5 × 10 × 60

= 3000 w

= 3 kw

Question 7: Two balls are thrown simultaneously in the air. The acceleration of the centre of mass of the two balls when in air

1. a. depends on the masses of the two balls
2. b. depends on the speeds of the two balls
3. c. is equal to g (Acceleration due to gravity)
4. d. depends on the direction of motion of the two balls

Solution:

As there is no force in the horizontal direction, so there will be no acceleration of COM in a horizontal direction.

As for vertical direction, the only gravitational force acts on both the balls, hence the acceleration of COM will be equal to the acceleration due to gravity which is ‘g’.

Question 8: The value of acceleration due to gravity at a depth of 1600 km is equal to [Radius of earth = 6400 km]

1. a. 9.8 ms–2
2. b. 19.6 ms–2
3. c. 4.9 ms–2
4. d. 7.35 ms–2

Solution:

Acceleration due to gravity at a depth “d”:

gd = g (1 - [d / Re])

d → 1600km

Re → 6400 km

g → 9.8 m / s2

gd = (9.8) (1 - [1600 / 6400])

gd = 7.35 ms–2

Question 9: ‘Young’s modulus is defined as the ratio of

1. a. tensile stress and longitudinal strain
2. b. hydraulic stress and hydraulic strain
3. c. shearing stress and shearing strain
4. d. bulk stress and longitudinal strain

Solution:

Young’s modulus is defined as the ratio of tensile stress to tensile strain or longitudinal strain.

Question 10: ‘Hydraulic lift’ works on the basis of

1. a. Stoke’s law
2. b. Toricelli’s law
3. c. Pascal’s law
4. d. Bernoulli’s law

Solution:

Hydraulic lift works on the principle of equal transmission throughout a fluid i.e. pascal’s law.

Question 11: The S.I. unit of specific heat capacity is

1. a. J mol–1 K–1
2. b. J kg–1 K–1
3. c. J K–1
4. d. J kg

Solution:

Specific heat capacity: S = (Q / mΔT)

Q → Amount of heat absorbed

M → Mass of the substance

T → Change in temperature of the substance

SI unit of S → J kg–1 K–1

Question 12: For which combination of working temperatures, the efficiency of ‘Carnot’s engine’ is the least?

1. a. 60K, 40 K
2. b. 40K, 20K
3. c. 80K, 60K
4. d. 100K, 80K

Solution:

The efficiency of Carnot’s engine; 𝜂 = 1 - [Tlower / Thigher]

Now, let’s check options.

(A) → 𝜂A = 1 - (40 / 60) = 0.33

(B) → 𝜂B = 1 - (20 / 40) = 0.5

(C) → 𝜂C = 1 - (60 / 80) = 0.25

(D) → 𝜂D = 1 - (80 / 100) = 0.2

Question 13: The mean energy of a molecule of an ideal gas is

1. a. 2 KT
2. b. [3 / 2] KT
3. c. KT
4. d. 1 / 2 KT

Solution:

Mean energy of a molecule of an ideal gas:

E = (1 / 2) mV2rms

Rms velocity of molecules: Vrms = √3KT / m

E = (1 / 2) × m × (3KT / m)

E = (3 / 2) KT

Question 14: Two simple pendulums A and B are made to oscillate simultaneously and it is found that A completes 10 oscillations in 20 sec and B completes 8 oscillations in 10 sec. The ratio of the lengths of A and B is

1. a. 8 / 5
2. b. 64 / 25
3. c. 5 / 4
4. d. 25 / 64

Solution:

The time period of the simple pendulum: T = 2π √(l / g)

lA / lB = [TA / TB]2

Time period of A: TA = 20 / 10 = 2 sec

Time period of B: TB = 10 / 8 = 5 / 4 sec

lA / lB = 64 / 25

Question 15: The waves set up in a closed pipe are

1. a. Transverse and progressive
2. b. Longitudinal and stationary
3. c. Transverse and stationary
4. d. Longitudinal and progressive

Solution:

The waves set up in a closed pipe are longitudinal and stationary because of the superposition of incident wave and reflected wave.

Question 16: Two spheres of electric charges +2 nC and −8 nC are placed at a distance‘d’ apart. If they are allowed to touch each other, what is the new distance between them to get a repulsive force of the same magnitude as before?

1. a. 4d / 3
2. b. 3d / 4
3. c. d
4. d. d / 2

Solution:

Case – I:

F = KqAqB / r2

F = [K . 2 . 8] / d2

F = 16K / d2

Case – II:

qA = qB = (2 - 8) / 2 = -6 / 2 = -3 nc

F’ = K (3) (3) / d2

But F = 16k / d2

16k / d2 = 9k / r2

r2 = (9 / 16) d2

r = (3 / 4) d

Question 17: Three-point charges of +2q, + 2q and –4q are placed at the corner A, B and C of an equilateral triangle ABC of side ‘x’. The magnitude of the electric dipole moment of this system is

1. a. 2 qx
2. b. 2 √3 qx
3. c. 3 √2 qx
4. d. 3 qx

Solution:

As evident from the diagram above, we can consider two dipoles one CA and CB. M1: Dipole moment of CA = 2q x (from C to A)

M2: Dipole moment of CB = 2qx (from C to B)

Net dipole moment = √[m12 + m22 + 2m1 m2 cos 60º]

= √[m12 + m22 + 2m1 m2 (1 / 2)]

= √[m12 + m22 + 2m1 m2]

= √(4q2x2 + 4q2x2 + 4q2x2)

= 2 √3 qx

Question 18: 4 × 1010 electrons are removed from a neutral metal sphere of diameter 20 cm placed in air. The magnitude of the electric field (in NC–1) at a distance of 20 cm from its centre is

1. a. 5760
2. b. 1440
3. c. 640
4. d. Zero

Solution:

Total charge removed from sphere = ne

= (4 × 1010) × (1.6 × 10–19)

= 6.4 × 10–9 C

Distance of point from centre of sphere = 20 cm = 0.2 m

Electric field: E = kq / r2

E = [9 × 109 × (6.4 × 10-9)] / (0.2)2

= 1440 N / C

Question 19: Two-point charges A = +3 nC and B = 1nC are placed 5 cm apart in the air. The work done to move charge B towards A by 1 cm is

1. a. 1.35 × 10–7 J
2. b. 2.7 × 10–7 J
3. c. 2.0 × 10–7 J
4. d. 12.1 × 10–7 J

Solution:

Potential energy of system: u = [KQAQB] / d

Initial distance between charges → 5 cm = 0.05m

Uinitial = [(9 × 109) × (3 × 10-9) × (1 × 10-9)] / 0.05

= 5.4 × 10–7 J

Ufinal = [(9 × 109) × (3 × 10-9) × (1 × 10-9)] / 0.04

= 6.75 × 10–7 J

Work done: W = uf – ui

W = (6.75 – 5.4) × 107

= 1.35 × 107 J

Question 20: A system of 2 capacitors of capacitance 2μF and 4μF is connected in series across a potential difference of 6V. The electric charge and energy stored in the system are

1. a. 10 μC and 30 μJ
2. b. 36 μC and 108 μJ
3. c. 8 μC and 24 μJ
4. d. 1 μC and 2 μJ

Solution:

Equivalent capacitance: Ceq = [C1C2] / [C1 + C2] = [2 × 4] / [2 + 4]

Ceq = 4μF / 3

Charge: q = cv

Q = (4 / 3) * 6 = 8μC

Energy stored: E = (1 / 2) CV2 = (1 / 2) (4 / 3) 62 = 24 μJ

Question 21: The minimum value of effective capacitance that can be obtained by combining 3 capacitors of capacitances 1pF, 2pF and 4pF is

1. a. (4 / 7) pF
2. b. 1 pF
3. c. (7 / 4) pF
4. d. 2 pF

Solution:

Minimum capacitance can be obtained by connecting these three capacitors in series.

(1 / Ceq) = (1 / C1) + (1 / C2) + (1 / C3)

= (1 / 1) + (1 / 2) + (1 / 4)

= [7 / 4]

Ceq = (4 / 7) pF

Question 22: A cylindrical conductor of diameter 0.1 mm carries a current of 90 mA. The current density (in Am–2) is (π ≃ 3)

1. a. 1.2 × 107
2. b. 2.4 × 107
3. c. 3 × 106
4. d. 6 × 106

Solution:

Current density: J = I / A

Current: I → 90 mA = 90 × 10–3 A

Diameter of wire: d = 0.1mm = 10–4 m2

The cross-section area of wire; A = πd2 / 4

A = [3 × (10-4)2] / 4 = 0.75 × 10–8 m2

J = [90 × 10-3] / [0.75 × 10-8] = 1.2 × 107 A / m2

Question 23: A piece of copper is to be shaped into a conducting wire of maximum resistance. The suitable length and diameter are _________ and ____________respectively.

1. a. L and d
2. b. 2 L and d
3. c. L / 2 and 2 d
4. d. L and d / 2

Solution:

Resistance of copper wire: R = ρL / A

ρ → Resistivity of material and is constant

L → Length of wire

A → Cross-sectional area of conductor

A = πd2 / 4

D → diameter of the wire

R ∝ L / d2

Now, let’s check the options

(A) RA ∝ (L / d2)

(B) RB ∝ 2 (L / d2)

(C) RB ∝ (1 / 8) (L / d2)

(D) RD ∝ 8 (L / d2)

Question 24: Of the following graphs, the one that correctly represents the I –V characteristics of a ‘Ohmic device’ is

Solution:

Ohmic device, obey ohm’s law, i.e. V = IR

V ∝ I (R → constant)

I – V characteristic will be a straight line

Question 25: The value of I in the figure shown below is

1. a. 8A
2. b. 21A
3. c. 19A
4. d. 4A

Solution:

We will use concepts of KCL i.e. Iin = Iout at a junction.

Using KCL at A

20 = 5 + I1

I1 = 15A

Using KCL at B

5 = 3 + I2

I2 = 2A

Using KCL at D

I1 + 4 = I3

I3 = 15 + 4

I3 = 19A

Using KCL at C

I = I2 + I3

I = 2 + 19

I = 21A

Question 26: The power dissipated in 3Ω resistance in the following circuit is

1. a. – 261 kJ
2. b. + 103 kJ
3. c. +261 kJ
4. d. –103 kJ

Solution:

The given circuit can be redrawn as

Again

I1 = I × (6 / [3 + 6]) = 0.75 × (6 / 9)

I1 = 0.5A

Power in 3Ω = I12R = (0.5)2 3 = 0.75W

Question 27: In metre bridge experiment, with a standard resistance in the right gap and a resistance coil dipped in water (in a beaker) in the left gap, the balancing length obtained is ‘I’. If the temperature of the water is increased, the new balancing length is

1. a. > 1
2. b. < 1
3. c. = 1
4. d. = 0

Solution:

Runknown / Rstandard = l / (1 - l)

As temperature increases Þ Resistance increases

Runknown / Rstandard increases ⇒ l / (1 - l) increases

(1 – l) should decrease ⇒ (l > 1)

Question 28: A proton, a deuteron and an α - particle is projected perpendicular to the direction of a uniform magnetic field with same kinetic energy. The ratio of the radii of the circular paths described by them is

1. a. 1 : √2 : 1
2. b. 1 : √2 : √2
3. c. √2 : 1 : 1
4. d. √2 : √2 : 1

Solution:

v = qBr / m ⇒ r = mV / qB

P = mV = √2mE, E is same (kinetic energy)

r = √2mE / qB

r ∝ √m / q

r = √m / q2

rp . rd . rα = √(m / e2) : √(2m / e2) : √(4m / e2)

= 1 : √2 : 1

Question 29: A galvanometer of resistance 50 Ω is connected to a battery of 3V along with a resistance of 2950 Ω in series shows full-scale deflection of 30 divisions. The additional series resistance required to reduce the deflection to 20 divisions is

1. a. 1500 Ω
2. b. 4440 Ω
3. c. 7400 Ω
4. d. 2950 Ω

Solution:

Total internal resistance = G + R

= 50 + 2950 = 3000Ω

Current; I = 3 / 3000 = 10–3A = 1 mA

If the deflection is to be reduced to 20 divisions

I’ = [1 mA / 30] * 20 = (2 / 3) mA

Let x be the effective resistance of the circuit.

3V = 3000 Ω × 1mA = x Ω * (2 / 3) mA

x = 4500 Ω

Resistance to be added = (4500 – 50) Ω

= 4450 Ω

≈ 4440 Ω

Question 30: The magnetic field at the centre of a current-carrying loop of radius 0.1 m is 5 √5 times that at a point along its axis. The distance of this point from the centre of the loop is

1. a. 0.2 m
2. b. 0.1m
3. c. 0.05m
4. d. 0.25m

Solution:

For a circular current-carrying loop of radius R

Bcentre = μ0i / 2R

Baxis = μ0iR2 / 2 [R2 + x2]3/2 [at a distance x from the centre]

Given Bcentre = 5 √5 Baxis

0i / 2R] = [5 √5] [μ0iR2 / 2 [R2 + x2]3/2]

[R2 + x2]3 / R6 = 125

[R2 + x2] / R2 = 5

x2 / R2 = 4

x = 2R

x = 2 × 10 = 20 cm = 0.2m

Question 31: A straight wire of length 50 cm carrying a current of 2.5 A is suspended in mid-air by a uniform magnetic field of 0.5 T (as shown in the figure). The mass of the wire is (g = 10 ms–2)

1. a. 62.5 gm
2. b. 250 gm
3. c. 125 gm
4. d. Cu2O + FeS

Solution:

For equilibrium

FB = mg

Bil = mg

m = Bil / g

m = [0.5 × 2.5 × 50 × 10-2] / 10 = 62.5 g

Question 32: Which of the following properties is ‘False’ for a bar magnet?

1. a. Its poles cannot be separated.
2. b. It points in North-South direction when suspended
3. c. It’s like poles repel and unlike poles attract.
4. d. It doesn’t produce a magnetic field

Solution:

A bar magnet can produce a magnetic field. Option (d) is False.

Question 33: A magnetic dipole of the magnetic moment 6 × 10–2 Am2 and moment of inertia 12 × 10–6 kgm2 performs oscillation in a magnetic field of 2 × 10–2 T. The time taken by the dipole to complete 20 oscillations is (π ≃ 3)

1. a. 36 s
2. b. 6s
3. c. 12 s
4. d. 18 s

Solution:

Time period of oscillation

T = 2π √I / MB

= 2π √[12 × 10-6] / [(6 × 10-2) (2 × 10-2)]

= 2π √(12 × 10-6) / (12 × 10-4)

= 2π × 10-1

For 20 oscillations,

T’ = 20 × 2π × 10–1

T’ = 12 sec

Question 34: The susceptibility of a ferromagnetic substance

1. a. >>1
2. b. > 1
3. c. < 1
4. d. zero

Solution:

Susceptibility of Ferromagnetic substance is >>>1 because it is strongly attracted to an external magnetic field.

Question 35: A bar magnet is allowed to fall vertically through a copper coil placed in a horizontal plane. The magnet falls with a net acceleration

1. a. = g
2. b. > g
3. c. < g
4. d. zero

Solution:

If the magnet is falling vertically down with its north pole towards the coil, then the upper face of the coil will become north pole, So that it can oppose the approaching north pole of the magnet. Here, the acceleration will be less than “g”.

Question 36: The working of magnetic braking of trains is based on

1. a. Alternating current
2. b. Eddy current
4. d. Pulsating current

Solution:

Working of magnetic breaking in the train is based on eddy current.

Question 37: A jet plane of wingspan 20 m is travelling towards the west at a speed of 400 ms–1. If the earth’s total magnetic field is 4× 10–4 T and the dip angle is 30º, at that place, the voltage difference developed across the ends of the wing is

1. a. 1.6 V
2. b. 3.2 V
3. c. 0.8 V
4. d. 6.4 V

Solution:

Voltage difference = BlV sin θ

= (4 × 10–4) × (20) × (400) sin 30º

= 1.6 V

Question 38: In the A.C. circuit shown, keeping ‘K’ pressed if an iron rod is inserted into the coil, the bulb in the circuit,

1. a. Glows more brightly
2. b. Glows less brightly
3. c. Glows with same brightness (as before the rod is inserted)
4. d. Gets damaged

Solution:

When the iron rod is inserted in the coil, then the inductive increases, hence the current flowing through the bulb decreases, therefore brightness decreases.

Question 39: The output of a step-down transformer is measured to be 48 V when connected to a 12 w bulb. The value of peak current is

1. a. (1 / √2) A
2. b. (√2) A
3. c. (1 / 2√2) A
4. d. (1 / 4) A

Solution:

P = V.I.

I = P / V

I = 12 / 48 = 0.25 A

Peak current = √2 I

= √2 * (1 / 4)

= (1 / 2√2) A

Question 40: A coil of inductive reactance (1 / √3) Ω and resistance 1Ω is connected to a 200 V, 50 Hz A.C. supply. The time lag between the maximum voltage and current is

1. a. (1 / 300) s
2. b. (1 / 600) s
3. c. (1 / 500) s
4. d. (1 / 200) s

Solution:

ω = 2πf

ω = 2 * 3.14 * 50

tan ϕ = xL / R = ωL / R = (1 / √3) / 1 = 1 / √3

ϕ = 30o

ωt = π / 6

t = π / [6 * ω]

t = [3.14] / [6 * 314]

t = (1 / 600) sec

Question 41: If E and B represent electric and magnetic field vectors of an electromagnetic wave, the direction of propagation of the wave is along

1. a. E
2. b. B
3. c. E × B
4. d. B × E

Solution:

As we know, by property of the electromagnetic wave, the electric field, magnetic field & the direction of propagation, all the three are mutually perpendicular. Thereby right-hand thumb rule using the figure. E × B.

Question 42: According to Cartesian sign convention, in ray optics

1. a. all distances are taken positive
2. b. all distances are taken negative
3. c. all distances in the direction of the incident ray are taken positive
4. d. all distances in the direction of the incident ray are taken negative

Solution:

In ray optics, all the directions in the direction of the incident ray are taken as positive.

Question 43: A linear object of height 10 cm is kept in front of a concave mirror of radius of curvature 15 cm, at a distance of 10 cm. The image formed is

1. a. magnified
2. b. magnified and inverted
3. c. diminished and erect
4. d. diminished and inverted

Solution:

Using mirror formula

(1 / f) = (1 / u) + (1 / v)

f = R / 2 = 15 / 2

(1 / [-15 / 2]) = (1 / -10) + (1 / v)

V = –30 cm

Magnification, m = −v/u = −30 / −10 = −3

Therefore, The image formed is real, magnified and inverted.

Question 44: During scattering of light, the amount of scattering is inversely proportional to _______ of the wavelength of light,

1. a. cube
2. b. square
3. c. fourth power
4. d. Half

Solution:

During scattering of light

Intensity: I ∝ (1 / λ4)

Question 45: In Young’s double-slit experiment if yellow light is replaced by blue light, the interference fringes become

1. a. wider
2. b. narrower
3. c. brighter
4. d. darker

Solution:

Fringe width: w = Dλ / d

w ∝ λ

But λyellow light > λblue light

Interference patterns will become narrower.

Question 46: According to Huygens’ principle, during refraction of light from air to a denser medium

1. a. Wavelength and speed decrease
2. b. Wavelength and speed increase
3. c. Wavelength increases but speed decreases
4. d. Wavelength decreases but speed increases

Solution:

Refractive index of the medium

μ = c / v

C → speed of light in vacuum or air

V → speed of light in the medium

Above equation implies that the speed of light decrease when it goes from rarer medium (air) to denser medium

Also; λ = v / f

λ = wavelength, f → frequency

Frequency remains the same for all medium unless the source of light is disturbed

λ V

Wavelength decreases.

Question 47: In a system of two crossed polarizers, it is found that the intensity of light from the second polarizer is half from that of the first polariser. The angle between their pass axes is

1. a. 45º
2. b. 60º
3. c. 30º
4. d. 0º

Solution:

From Malus law

I = I0 cos2 θ

There; I = I0 / 2

I0 / 2 = I0 cos2 θ

cos θ = 1 / √2

θ = 45o

Question 48: From the following graph of photocurrent against collector plate potential, for two different intensities of light I1 and I2, one can conclude

1. a. I1 = I2
2. b. I1 > I2
3. c. I1 < I2
4. d. Comparison is not possible

Solution:

The value of photocurrent depends on the intensity of incident light. So, when the intensity of incident light increases, then the value of photocurrent is increased. The intensity of light photocurrent.

I1 < I2

Question 49: A particle is dropped from a height ‘H’. The de’Broglie wavelength of the particle depends on height as

1. a. H
2. b. H0
3. c. H1/2
4. d. H–1/2

Solution:

From de-broglie expression

λ = h / mv

λ = h / [m √2gH]

λ ∝ H–1/2

Question 50: The scientist who is credited with the discovery of ‘nucleus’ in an atom is

1. a. J.J. Thomson
2. b. Rutherford
3. c. Niels Bohr
4. d. Balmer

Solution:

Rutherford is credited with the discovery of nucleus in an atom.

Question 51: The energy (in eV) required to excite an electron from n = 2 to n = 4 state in the hydrogen atom is

1. a. + 2.55
2. b. – 3.4
3. c. – 0.85
4. d. + 4.25

Solution:

The expression of energy is En = 13.6 / n2

The required energy is E = E2 - E4 = (13.6 / 22) - (13.6 / 42)

= +2.55

Question 52: In a nuclear reactor the function of the Moderator is to decrease

1. a. Number of neutrons
2. b. Speed neutrons
3. c. Escape of neutrons
4. d. Temperature of the reactor

Solution:

In a nuclear reactor, the function of the moderator is to decrease the speed of neutrons.

Question 53: The particles emitted in the decay of 23892U to 23492U

1. a. 1 α and 2 β
2. b. 1 α only
3. c. 1 α and 1 β
4. d. 2 α and 2 β

Solution:

∴ 1 α and 2 β particles

Question 54: The mass defect of 42He is 0.03μ. The binding energy per nucleon of helium (in MeV) is

1. a. 27.93
2. b. 6.9825
3. c. 2.793
4. d. 69.825

Solution:

The mass defect of 42He; ΔM = 0.03u

Binding energy of helium: E = ΔM × 931 MeV

E = 0.03 × 931.5 = 27.93 MeV

Number of nucleons in helium; n = 4

Binding energy per nucleon = E / n = 27.93 / 4 = 6.9825

Question 55: The energy gap in case of which of the following is less than 3 eV?

1. a. copper
2. b. Iron
3. c. Zener diode
4. d. Germanium

Solution:

In Germanium energy the gap is less than 3eV.

Question 56: Which of the following semiconducting devices is used as a voltage regulator?

1. a. Photo diode
2. b. LASER diode
3. c. Zener diode
4. d. Solar cell

Solution:

Zener diode is used as a voltage regulated as in reverse biased condition it exhibits constant voltage.

Question 57: In the three parts of a transistor, ‘Emitter is of

1. a. Moderate size and heavily doped
2. b. Large size and lightly doped
3. c. Thin size and heavily doped
4. d. Large size and moderately doped

Solution:

In the case of a transistor, the emitter is of moderate size and heavily doped so as to supply a large number of majority charge carriers for current flow.

Question 58: In the figure shown, if the diode forward voltage drop is 0.2 V, the voltage difference between A and B is

1. a. 1.3 V
2. b. 2.2 V
3. c. 0
4. d. 0.5 V

Solution:

The voltage drop across AB by using KVL is as follows:

VAB = (0.2 × 10-3 × 5 × 103) + 0.2 + (0.2 × 10-3 × 5 × 103)

= 1 + 0.2 + 1

= 2.2V

Question 59: Which of the following logic gates is considered as ‘universal’?

Solution:

NAND and NOR gates are considered as universal gates. Out of the given options, an option (D) is NAND gate.

Question 60: A basic communication system consists of

(a) Transmitter

(b) Information source

(c) User of information

(d) Channel

1. a. a, b, c, d and e
2. b. b, a, d, e and c
3. c. b, d, a, c and e
4. d. b, e, a, d and c

Solution:

format: plain