Page 147 - Science Class 07

I All light comes from atoms when they gain extra energy either from another source or on
getting excited when struck by other particles. This extra energy begins to emit light.
I When the light strikes on any object it bounces off in all directions. This is called scattering
of light.
i The sun, stars, fire flies, etc. are natural sources of light.

i Electric lights, candles, oil-lamps, torches, lasers, etc. are artificial sources of light.
i Light always travels in a straight line.
i Light travels with a speed of 312500 km per second approximately.

i The angle of incidence is equal to the angle of reflection.
i The normal, the incident ray and the reflected ray— all are in the same plane.
i A plane mirror is a smooth surface that reflects most of the light striking it.

i Lateral inversion is a phenomenon in which left hand side of an object appears as right hand
side and vice-versa.

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Exercise
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A. Tick (3) the correct op on.
1. Which of the following is not a natural source of light?
(a) Sun (b) Star
(c) Fire flies (d) Candle

2. When an object is place at the centre of curvature before a concave mirror, the image will
be formed at:

(a) at focus (b) at centre of curvature
(c) at P (d) between F and P
3. The speed of light is _____________ km per second.

(a) 312500 (b) 235400
(c) 576800 (d) 107500
4. Angle of incidence is _____________ to/than angle of reflec on.
(a) equal (b) double

(c) more (d) less
5. Which of the following objects gives regular reflec on?
(a) Stone (b) Wood

(c) Mirror (d) Brick
B. Fill in the blanks.
1. The brightness produce by a light-source is called its _____________ intensity.
2. The objects both natural or man-made, that give out light from their bodies are called
_____________.
3. Light always travels in a _____________ .

Science-7 147