Question

The angle between incident ray and reflected ray is 60°.

What is the angle of incidence?


Class 8​

Answer 1

${\underline {\underline {\boxed {\sf \pink { 30^\circ} }}}}$

Here, we are given that the angle between incident ray and reflected ray is 60°.We have to find the angle of incidence.

★ Angle between incident ray and reflected ray = ∠ i + ∠ r

• ∠ i = angle of incidence
• ∠ r = angle of reflection

We know that,

★ The angle of incidence and the angle of reflection are always equal.

So, let us assume both angle of incidence and the angle of reflection as "x°" each.

According to the question,

★ Angle between incident ray and reflected ray = ∠ i + ∠ r

→ 60° = x° + x°

→ 60° = 2x°

→ $\sf \dfrac{60^\circ}{2}$ = x°

→ 30° = x

We get thar

∠ i = 30°

∠ r = 30°

Therefore,

• Measure of angle of incidence is 30°.

_____________________________

Laws of reflection:

→ The incident ray, the reflected ray and the normal at the point of incidence lie on the same plane.

→ The angle of incidence is equal to the angle of reflection. (∠ i = ∠ r)

Answer 2

Angle between incident ray and reflected ray is 60°.

We know that ∠i = ∠r (2nd law of reflection)

∴ ∠i + ∠r = 60°

⇒ 2∠i = 60°

⇒ ∠i = 30°.

So, the angle of incidence = 30°.

More:-

• δ = 180° - (∠i + ∠r) [Angle of deviation].
• If an object moves toward a plane mirror by a speed of (v), then the image also comes towards it at a speed of (v). But the image comes towards it at (2v) w.r.t. it.