Exams › JEE Main › Physics

Directions: Questions number 10-12 are based on the following paragraph. An initially parallel cylindrical beam travels in a medium of refractive index μ(I) = μ0 + μ2 I, where μ0 and μ2 are positive constants and I is the intensity of the light beam. The intensity of the beam is decreasing with increasing radius. The speed of light in the medium is

1. minimum on the axis of the beam
2. the same everywhere in the beam
3. directly proportional to the intensity I
4. maximum on the axis of the beam

Correct answer: minimum on the axis of the beam

Solution

Refractive index mu = mu0 + mu2*I with mu2 > 0, so mu is largest where I is largest, i.e. on the axis. Since v = c/mu, the speed is minimum on the axis of the beam.

Related JEE Main Physics questions

• A telescope is fitted with an objective lens of focal length 100 cm and an eyepiece of focal length 5 cm. If the final image is adjusted to form at the least distance of distinct vision, what is the telescope’s magnifying power?
• An object placed 2.4 m in front of a lens produces a clear image on a film located 12 cm behind the lens. A 1 cm thick glass slab of refractive index 1.50 is then inserted between the lens and the film, with its plane surfaces parallel to the film. To obtain a sharp image again on the film, to what distance from the lens must the object be moved?
• A light ray is incident on an equilateral prism in such a way that the angle of incidence equals the angle of emergence, and this common angle is three-fourths of the prism angle. What is the angle of deviation produced?
• A glass lens with refractive index 1.60 has a focal length of +20 cm when placed in air. If the same lens is immersed in water of refractive index 1.33, its focal length will be
• A prism is placed in air. If a ray is incident at 60° and the prism angle, the deviation angle δ, and the angle of emergence e are all equal, what is the refractive index of the prism?
• A person’s farthest point of clear vision is 30 cm from his eyes. If he wants to read a book held 50 cm away, what power of lens should he use?

⚔️ Practice JEE Main Physics free + battle 1v1 →