Review for Test 2
Here are some problems from last years exams:
a) T F Electrons tend to move uphill in potential.
b) T F A charge moving along an equipotential will not experience a change of
c) T F Electric field lines are orthogonal to equipotential lines.
d) T F When a positive charge moves along the Electric field lines its Kinetic
e) T F In a parallel plate capacitor, the capacitance is independent of the material
between the plates.
f) T F The plates of a parallel plate capacitor have an area of .004 square meters and
are separated by a distance of .2mm so the capacitance is 177 pF.
g) T F Current is defined to be the amount of charge that flows.
h) T F Resistivity is proportional to conductivity.
i) T F If the charge on the plates of a capacitor doubles when a dielectric is placed
between the plates, the dielectric constant is k = 2.
j) T F The direction of a current is the same as the flow of the electrons.
1.(2pts each) Note: Some are fill in the blank.
a) T F The source that converts some form of energy into electrostatic potential
energy is a source of emf.
b) T F A real source of emf has no internal resistance.
c) __________ loop rule: The algebraic sum of the changes in potential around a closed loop is zero
d) The __________ is the time needed for the charge on a capacitor to drop to 50%
of its initial value.
e) T F No one has ever found a magnetic monopole.
f) If a proton is traveling from left to right across this page and a magnetic field
is projecting out from the page, the force acting on the proton would point
g) The net force on a current loop in a uniform magnetic field is ____________.
i) T F The torque experienced by a current-carrying coil in a magnetic field is used
j) T F Ohmís law relates current and capacitance.
5.)(10pts) Find the equivalent capacitance of the figure:
6.)a)(5pts) A 2mF parallel plate capacitor is connected to a 9V battery. A dielectric slab with a dielectric constant of 5 is inserted to fill the space between the plates. Find the additional charge that flows to the plates.
b)(5pts) When 12V is applied across a wire of length 200cm and radius 1mm, a current of 3mA flows through the wire. Find the resistivity of the material.
7.)(10pts) A toaster operates at 120V with a current of 8A. It takes 45sec to toast a slice of bread. At 8 cents per kilo-watt-hour, what does it cost to toast a slice of bread?
4.a)(7pts) A 2-mF capacitor is connected in parallel with a battery and a resistor. When the battery is disconnected the charge on the capacitor falls to 37% of its initial value in 3 ms. What is the resistance.
b)(8pts) In an RC charging circuit, R = 1000W, and C = 5-mF. How long will it take to charge the capacitor to 80% of its final value?