PHYSICS [5 Mark Question Answer]

(i) the angle of incidence
(ii) the angle of reflection

ON is normal on the plane mirror at point O
ON is perpendicular on a plane mirror
Angle of incidence ∠i = ∠AON
and angle of reflection ∠r = ∠BON
Since, ∠i – ∠r
∠AOB = 30°
⇒ ∠AON + ∠BON = 30°
⇒∠i + ∠i – 30°
⇒ 2 ∠i =30°
⇒ ∠i = 30 / 2 = 15°
∴Angle of incidence = ∠i = 15°
and Angle of reflection ∠i = 15°

(i) The incident ray, the reflected ray and the normal at the point of incidence, lie in the same plane.
(ii) The angle of incidence and angle of reflection are equal i.e. ∠i = ∠r.
Verification
Take a wooden drawing board and fix a white sheet of paper on it. In the middle of paper draw a straight line KK\ Mark a point B on it. Draw a perpendicular BN. Place a mirror XX’ on line KK’ such that polished side of mirror is along the line. Hold-the mirror in the mirror holder.

Fix two steel pins P and Q on the straight line AB atleast 10 cm apart. Look for the images of the pins P and Q and fix two pins P Q’ such that P’, Q’ and images of P and Q are all in the same straight line. Remove the pins and draw small circles around the pin pricks.
Remove the mirror also. Join P’Q’ and produce the straight line to meet at B.
Measure ∠ABN = i and ∠CBN = r.
It is found that ∠i = ∠r. This proves that Angle of Incidence is equal to Angle of Reflection.
As the incident ray, the reflected ray and the normal lie in the plane of paper, therefore, they lie in the same plane.

incident ray— The ray of light falling on the surface AB is called the incident ray. In the following figure, PN is the incident ray.
Reflected ray— The incident ray bouncing back in the same medium after striking the reflecting surface is called a reflected ray. In the following figure, NQ is the reflected ray.

Angle of incidence - The angle formed between the incident ray and the normal is the angle of incidence. (PNM is the angle of incidence.)

Angle of reflection - The angle formed between the normal and the reflected ray is called angle of reflection (MNQ is the angle of reflection)

Normal - It is the line drawn perpendicular to the reflecting surface at the point of incidence. MN is normal.

(a). A light ray passes             from air to glass	(5). slows down
(b). A light ray passes             from glass to water	(1) . speeds up
(c). Virtual image	(4). plane mirror
(d). Red rose	(2). reflects red light
(e). Red, green, and               blue	(3). primary colours