Chapter 5 · ICSE Class 8 Physics (Selina Concise)

Light Energy

Learn about the velocity and refraction of light as it passes between different media.

💡 Chapter 5

Light bending as it passes from air into water, called refraction A light ray travelling through air hits the surface of water and bends toward the normal line as it enters the denser water, illustrating refraction Air Water bends toward normal
5.1

Velocity of Light

Light travels at about 3×10⁸ m/s in air/vacuum, but slower in denser media like water or glass.

1

Does light travel faster in air or in water?

Air — light slows down when passing into denser media like water

2

What is the approximate speed of light in vacuum?

3×10⁸ m/s (300,000 km/s)

5.2

Refraction of Light

Refraction is the bending of light as it passes from one medium to another due to a change in speed.

1

Why does a pencil appear bent when placed in a glass of water?

Light refracts (bends) as it passes from water to air, making the pencil appear to shift at the water's surface

2

What causes light to bend when it enters a denser medium?

The change in light's speed as it enters a medium with a different density

Practice

Exercises

1. What is the approximate speed of light in air?

2. What is refraction?

3. Why does a straw in a glass of water appear bent?

4. Does light speed up or slow down when entering glass from air?

5. What causes refraction to occur?

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