Question

When a ray of light travels from a rarer medium to a denser medium obliquely,

• A. it bends towards the normal.
• B. it bends away from the normal.
• C. it goes undeviated.
• D. it is reflected back.

Answer 1

The correct option is A

it bends towards the normal.

The explanation for the correct option -

(a) it bends toward the normal

1. The refractive index for an optically denser medium is higher than the refractive index of a rarer medium.
2. $opticaldensity\alpha \frac{1}{speedoflight}$
3. So if the refractive index is high then the speed of light in that medium will be less.
4. Since the light is traveling from a rarer medium to a denser medium, its speed reduces and therefore it bends towards the normal.

The explanation for the incorrect options -

(b) It bends away from the normal

1. The light bends away from the normal when it travels from a denser medium to a rarer medium due to an increase in its speed.

(c) It goes undeviated

1. A ray of light, when travels from one transparent medium to another, goes undeviated only if it is incident normally on the boundary surface of the medium.

(d) It is reflected back

1. Light rays will reflect back when the surface is oblique and reflecting or the total internal reflection phenomena are satisfied.
2. For the total internal reflection to happen the light must travel from the denser to a rarer medium.
3. Both conditions are not satisfied, hence the light will not reflect back. Hence, option (d) is incorrect.

Final answer: Hence, option (a) is correct.