why incident ray are equal to the reflected ray?
The following experiment proves that the incident ray is equal to reflected ray:
Take a white card board sheet and fix the same firmly on a board. Draw a thick line MM’ and mark the midpoint O. Draw a perpendicular ON at O. Place a plain mirror on MM’ with its center at O.Take three pins and fix them vertically on the sheet at positions C, B and A on one side of ON such that the pins lie on a straight line when viewed from A. Now move to the other side of the perpendicular ON and fix three more pins at F, E and D in such way that the images A’ B’ C’ of the pins at A, B, C and the pins at D, E, F are all in one straight line. This is the most important point of the entire experiment.
Now remove the mirror and the pins carefully marking the points where they have been fixed. At this stage we will not be able to locate the positions of A’, B’ and C’. Draw a perpendicular AP from A and extend that line. Join DO and extend that too. Let A’ be the point of intersection of these extended line. A’ is nothing but the position of the image that appeared when the mirror was there. Same way locate the positions of B’ and C’.
If you join AO and measure the angles AON and DON, you will find them to be equal. Thus, it proves the angle of incidence equals angle of reflection. Also you will notice that the following measures to be equal. AP = PA’, BQ = QB’ and CR = RC’, which proves the image distance equals the object distance.