Page 99 - Viva ICSE Science 4 : E-book

TERMS TO KNOW

1. Luminous objects: Objects that emit light of their own
2. Non-luminous objects: Objects that refl ect light of luminous objects
3. Vacuum: Empty space
4. Refl ection: Light falling on a surface and bouncing back
5. Refraction: Slight change in the direction of light as it passes through a diff erent medium
6. Transparent: Materials through which light passes easily
7. Translucent: Materials through which only little amount of light can pass
8. Opaque: Materials through which light cannot pass at all

QUICK LOOK

1. Light helps us to see things around us.
2. Light is a form of energy.
3. The objects that emit light of their own are called luminous objects. Some examples are
the sun, the stars, torch and lamp.

4. The objects which do not emit light of their own are called non-luminous objects. Some
examples are chair, table and glass.
5. Sun is a natural source of light.

6. Electric bulb, candle, torch and laser light are some artifi cial sources of light.
7. Light travels in straight line in the form of rays.
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8. Light travels very fast, at the speed of 3 × 10 m/s.
9. Light travels in all directions from its source.
10. Light can travel through empty space.
11. Light can be absorbed, refl ected and refracted.
12. Light passes through transparent material easily.
13. Little amount of light can pass through translucent material.
14. Opaque materials do not allow any light to pass through them.
15. A shadow is formed when light coming from a source is blocked by an object.

EXERCISES

A. Fill in the blanks.

1. Light is a form of ____________ that makes objects visible to our eyes.
2. The ____________ is the major natural source of light on earth.

3. Colour of shadow always appears ____________.

4. Length of shadow is shortest at ____________.

5. Light can also travel through ____________ space.

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