Refraction of Light

When light travels from one transparent medium to another, its speed changes. Due to this change in speed, the light ray generally changes its direction. This phenomenon is called refraction of light.

Refraction explains many common observations such as a pencil appearing bent in water, the apparent shallowness of a swimming pool, and the reappearance of a coin when water is poured into a vessel.

The change in the direction of the path of light when it passes from one transparent medium to another transparent medium is called refraction. The refraction of light is essentially a surface phenomenon.

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When light passes from one transparent medium to another, its speed and direction change. This is called refraction.

Refracted light is the part of light enters into the other medium and travels in a straight path but in a direction different from its initial direction and is called the refracted light.

When travelling obliquely from one medium to another, the direction of propagation of light in the second medium changes. This phenomenon is known as refraction of light.

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Light changes its direction when going from one transparent medium to another transparent medium. This is called the refraction of light.

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The bending of the light ray from its path in passing from one medium to the other medium is called 'refraction' of light.

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When a ray of light impinges on a polished, smooth, shiny surface, the rebounding of light within the same medium is called reflection of light.

The ray that enters the second medium after crossing the boundary is called the refracted ray.

A normal is an imaginary line drawn perpendicular to the boundary at the point of incidence.

Different transparent media allow light to travel at different speeds. When light passes from one medium to another, its speed changes, and this causes a change in direction except when the ray is incident normally.

Rule of bending

The laws of refraction are fundamental for board examinations and objective tests.

First law

The incident ray, the refracted ray, and the normal at the point of incidence all lie in the same plane.

Second law

For a given pair of media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction remains constant.

\[\frac {\text {sin i}}{\text {sin r}}\] = constant

This constant is called the refractive index of the second medium with respect to the first medium.

Snell's Law

Pencil in Water (Observing Refraction):

• Take a transparent glass and fill it with water.
• Dip a pencil vertically into the water and observe its thickness.
• Tilt the pencil at an angle and observe again.
• In both cases, the portion of the pencil inside the water appears thicker than the portion above.
• When the pencil is tilted, it looks bent or broken at the water's surface.

This effect occurs because light changes direction (refracts) when it moves from water to air. The bending of light makes the pencil appear distorted, demonstrating the refraction of light.

Disappearing and Reappearing Coin

• Place a 5-rupee coin in a metallic vessel.
• Slowly move away until the coin disappears from view.
• Ask a friend to pour water into the vessel while you keep looking in the same direction.
• As the water level rises, the coin becomes visible again.

Light rays coming from the coin bend when passing from water to air, changing their path. This makes the coin, which was earlier invisible, appear again due to the refraction of light.

Refraction of Light Through a Glass Slab:

• Place a glass slab on a paper and draw its outline (PQRS).
• Draw an inclined ray (AN) on side PQ, marking point N where it meets the slab.
• Fix two pins (A and B) along the ray and look from the other side.
• Align two more pins (C and D) with the images of A and B.
• Remove the slab and draw a line through C and D, meeting SR at point M.
• Join M and N to trace the path of the refracted ray.

Refraction of light passing through a glass slab

Observation and Explanation:

1. The incident ray (AN) strikes the glass at point N and bends due to refraction.

2. The first refraction occurs when light moves from air to glass at N, bending toward the normal.

3. The second refraction occurs when light moves from glass to air at M, bending away from the normal.

The angles of refraction are measured as:

• i = angle of incidence (AN to normal at N).
• r = angle of refraction at N.
• i₁ = r, meaning the refraction inside the glass follows the same pattern.
• e = emergent angle, which equals i due to the opposite bending effect.

The emergent ray (MD) is parallel to the incident ray (AN) but is slightly displaced from it due to the shift caused by the refraction process.

This activity shows that light bends when passing between different transparent media, following the laws of refraction. The incident and emergent rays remain parallel but are slightly displaced, demonstrating the refraction through a rectangular glass slab.