1.

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 theta, the spot of the light is found to move through a distance y on the scale. The angle theta is given by

Answer»

`y/x`
`(x)/(2y)`
`x/y`
`(y)/(2x)`

SOLUTION :
When plane mirror is given rotation of `theta`, then REFLECTED ray will have rotation `2THETA`. In figure,
In right angle triangle tan`2theta=y/x`
For smaller angle, `tan2theta ~~2 theta`
`therefore 2 theta=y/x therefore theta=(y)/(2x)`


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