A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle θ, the spot of the light is found to move through a distance y on the scale. The angle θ is given by:
y/2x
x/2y
y/x
x/y
Solution:
The correct option is B (x/2y) If mirror is rotated by angle θ, angle of reflection is 2θ tan2θ = y/x 2θ = y/x θ = y/2x