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The bending of light rays when they pass from one medium to another is called:
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Answer: Option D — Refraction
Detailed Solution
Refraction is the change in direction (bending) of light when it passes obliquely from one transparent medium to another, such as from air into water or glass. It happens because light travels at different speeds in different media. Light travels fastest in a vacuum (about 3 × 10⁸ metres per second) and slower in denser media such as water and glass.
When light enters an optically denser medium (where it travels slower), it bends towards the normal (the imaginary line perpendicular to the surface). When it enters an optically rarer medium (where it travels faster), it bends away from the normal. If light falls along the normal (at 90° to the surface), it passes straight through without bending, though its speed still changes.
The laws of refraction are:
The incident ray, the refracted ray and the normal at the point of incidence all lie in the same plane.
The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media. This is Snell's law, named after the Dutch scientist Willebrord Snell (1621). The constant is called the refractive index.
The refractive index of a medium is the ratio of the speed of light in a vacuum to its speed in that medium. Water has a refractive index of about 1.33, ordinary glass about 1.5, and diamond about 2.42.
Everyday examples of refraction:
- A pencil partly dipped in water appears bent at the surface.
- A swimming pool or a pond appears shallower than it really is.
- Stars twinkle because of refraction by layers of air with different densities.
- The Sun is visible for about 2 minutes before actual sunrise and after actual sunset, due to atmospheric refraction.
- Lenses in spectacles, cameras and microscopes work by refraction.
- Total internal reflection, a special case, explains the sparkle of diamonds, mirages and optical fibres.
Why not the other options?
- ✗Reflection is the bouncing back of light from a surface.
- ✗Diffraction is the bending of light around the edges of an obstacle or through a narrow slit.
- ✗Polarisation restricts the vibrations of light to a single plane.
Quick tip
Remember: Refraction = bending of light between media (Snell's law); examples: bent pencil in water, twinkling stars, early sunrise; refractive index of water 1.33, glass 1.5, diamond 2.42.
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Light & Optics — Preparation
This question tests your understanding of Light & Optics, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers the nature of light, reflection and refraction, mirrors and lenses, total internal reflection, dispersion and scattering of light, the human eye and its defects, optical instruments, and the colours of objects. Exams test the phenomena behind everyday sights: the sky looks blue because of the scattering of light, rainbows form through dispersion and internal reflection, diamonds sparkle because of total internal reflection, and mirages are caused by refraction. Know which lens corrects which defect (concave lenses for myopia and convex lenses for hypermetropia). Practise the light and optics questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.