Question

A ray of light strikes a plane mirror $PQ$ at an angle of incidence of ${30^ \circ }$,is reflected from the plane mirror $QR$ placed at right angles to the first mirror. the angle of reflection at the second mirror is –
Draw a ray diagram to illustrate your answer.
A. ${30^ \circ }$
B. ${45^ \circ }$
C. ${60^ \circ }$
D. ${90^ \circ }$

Answer 1

Hint:Reflection is the bouncing back of light rays after hitting any surface which is smooth, shiny and polished. Laws of Reflection – (i) The incident ray, the reflected ray and the normal lie in the same plane. (ii) The angle of reflection is equal to the angle of incidence.

Complete step by step answer:

Ray $AB$ strikes the mirror $PQ$ at $B$. The angle of incidence is ${30^ \circ }$ and gets reflected as $BC$. The angle of reflection $\angle NBC$ is${30^ \circ }$ following the law of reflection. When the reflected ray $BC$ strikes at the surface of another mirror $QR$ , $\angle NBC = \angle BCQ$$ = $ ${30^ \circ }$ . The angle of incidence of ray $BC$ is $\angle MCQ - \angle BCQ = {90^ \circ } - {30^ \circ } = {60^ \circ }$. Therefore, the angle of reflection at the second mirror is ${90^ \circ }$.

Hence, the correct answer is option D.

Note:Reflection is a surface phenomenon. Meters like ammeters and voltmeters use a mirror to avoid parallax error. The reading is taken from a position such that the image of the pointer is directly under the pointer. The wing and rear-view mirrors of a car are made of a convex and a plane mirror respectively. The two wing mirrors enable the driver to see objects on both sides of the car. The rear-view mirror enables the driver to see things behind the car. A microscope uses a mirror to reflect light to the specimen under the microscope.