Question

A ray of light travelling in water is incident on its surface open to air. The angle of incidence is θ, which is less than the critical angle. Then, there will be ______.

Options

• only a reflected ray and no refracted ray.

• only a refracted ray and no reflected ray.

• a reflected ray and a refracted ray and the angle between them would be less than 180° − 2θ.

• a reflected ray and a refracted ray and the angle between them would be greater than 180° − 2θ.

Answer 1

A ray of light travelling in water is incident on its surface open to air. The angle of incidence is θ, which is less than the critical angle. Then, there will be a reflected ray and a refracted ray and the angle between them would be less than 180° − 2θ.

Explanation:

The light ray travels from a dense media (water) to a rarer medium (air). As stated, the incident angle (θ) is less than the critical angle. The incident beam AB generates both a reflected ray BC and a refracted ray BD. The angle of refraction (r) will be larger than the angle of incidence (θ).

The angle Φ (say) between reflected ray BC and refracted ray BD is

Φ = 180° − r − θ

Since, r > θ, Φ < 180° − 2θ.