Updated: September 2026
REFRACTION
REFRACTION – DEFINITION
Refraction is the peculiarity of twisting(bending) light starting with one medium then onto the next medium.
LAWS OF REFRACTION
Refraction of light follows two laws:
First Law: The incident ray, the refracted ray, and the normal to the interface at the point of incidence all lie in the same plane.
Second Law (Snell’s Law): For a given pair of media and a given colour of light, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant. This constant is the refractive index of the second medium with respect to the first:
n₁ sin θ₁ = n₂ sin θ₂
where θ₁ is the angle of incidence, θ₂ is the angle of refraction, and n₁, n₂ are the refractive indices of the first and second media.
REFRACTION OF LIGHT – IMAGE
REASON FOR REFRACTION
The reason for refraction of light is because of the adjustment(change) of speed of light starting with one medium then onto the next.
At the point when the beam of light goes from rarer to denser , the the angle of incidence is more prominent(greater) than that of the angle of refraction. The refracted beam twists(bends) towards the normal.
At the point when the beam of light goes from denser to rarer,angle of incidence is less than the angle of refraction.The refracted beam twists (bends)away from the normal.
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RARER TO DENSER BENDS TOWARDS THE NORMAL (RDT) DENSER TO RARER BENDS AWAY FROM THE NORMAL (DRA) |
REFRACTIVE INDEX
Refractive index is the proportion of speed of light in vacuum to the speed of light in medium.
MEANING OF REFRACTIVE INDEX
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The refractive index provides data in regards to the guidance of direction of bending of light
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Gives important data about the critical angle.
REFRACTIVE INDEX VALUES
- For vacuum the value is 1
- For air the value is 1.0003
- For water, the value is 1.33
- For glass the value is 1.5
- For diamond the value is 2.42
INSTANCES OF DAILY LIFE
- A spoon or straw appears bent at the point where it enters a glass of water
- A diamond’s sparkle comes partly from refraction bending light sharply as it enters and exits the stone
- The apparent raised bottom of a swimming pool or pond when viewed from above
- A rainbow forms when sunlight refracts and disperses through raindrops
A spoon appears bent in a glass of water” and “The sparkle of a diamond (an application of total internal reflection combined with refraction).”
SOLVED EXAMPLES
Example 1. A ray of light travels from air into water. The angle of incidence is 45°, and the angle of refraction is 32°. Find the refractive index of water with respect to air.
Solution: n = sin θ₁ / sin θ₂ = sin 45° / sin 32° = 0.707 / 0.530 = 1.33
Example 2. The refractive index of glass with respect to air is 1.5. If light enters glass from air at an angle of incidence of 30°, find the angle of refraction.
Solution: n = sin θ₁ / sin θ₂ 1.5 = sin 30° / sin θ₂ sin θ₂ = 0.5 / 1.5 = 0.333 θ₂ = 19.5° (approximately)
Example 3. The speed of light in vacuum is 3 × 10⁸ m/s. If the refractive index of a medium is 1.5, find the speed of light in that medium.
Solution: n = c / v v = c / n = (3 × 10⁸) / 1.5 = 2 × 10⁸ m/s
EXAMPLE
REFRACTION THROUGH A GLASS SLAB
REFRACTION THROUGH A GLASS PRISM
REFRACTION OF LIGHT: FREQUENTLY ASKED QUESTIONS (FAQ)
What is refraction of light? Refraction is the bending of light as it passes from one transparent medium into another, caused by a change in the speed of light between the two media.
What are the laws of refraction? First, the incident ray, refracted ray, and normal all lie in the same plane. Second (Snell’s law), 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.
Why does light bend when it enters a denser medium? Light slows down when entering a denser (higher refractive index) medium, which changes its direction — it bends toward the normal. The reverse happens entering a rarer medium: light speeds up and bends away from the normal.
What is the refractive index? The ratio of the speed of light in a vacuum to the speed of light in a given medium. It tells you how much a medium bends light and, indirectly, its critical angle for total internal reflection.
Does the colour of light affect refraction? Yes — different wavelengths (colours) refract by slightly different amounts in the same medium, which is why a prism splits white light into a spectrum (dispersion).
How is refraction different from reflection? Reflection is light bouncing back into the same medium; refraction is light passing into a new medium and changing direction due to a change in speed.
What is an everyday example of refraction? A pencil or straw appearing bent where it enters a glass of water — see “Instances of Daily Life” above.
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