General Science Question Answers Chapter 17 Class 7 Maharashtra Board

Question Answers For All Chapters – General Science Class 7

Effects of Light

1. Fill in the blanks:

(a) When the beams from the headlights of a car fall on an object in the night, the shadows called umbra and penumbra can be seen.

(b) During a lunar eclipse, the shadow of the earth falls on the moon.

(c) During a solar eclipse, the shadow of the moon falls on the earth.

(d) Various shades of colour are seen in the sky at sunrise and sunset due to scattering of light.

2. Give reasons:

(a) Space beyond the earth’s atmosphere appears dark.

→ There is no atmosphere in space to scatter sunlight, so no light is reflected, making it appear dark.

(b) We are able to read while sitting in the shade.

→ Light scatters from surrounding objects and reaches our eyes, allowing us to see even in the shade.

(c) We should not observe the solar eclipse with naked eyes.

→ The sun’s rays during an eclipse include harmful ultraviolet (UV) radiation, which can damage the eyes permanently.

3. Give some examples of the scattering of light that we come across in day-to-day life.

✔ The blue sky is due to the scattering of sunlight by air molecules.

✔ The red and orange colors at sunset and sunrise happen due to the longer path of light through the atmosphere.

✔ Dust particles in a beam of sunlight make the light visible in a dark room.

✔ The bluish color of smoke is due to scattering.

4. Why is the shadow of a bird flying high not seen on the earth?

• The bird is far from the ground, and its shadow spreads out and fades before reaching the surface.
• The scattering of light also reduces the sharpness of its shadow.

5. Why is a penumbra not obtained from a point source?

• A point source of light emits light rays from a single location, creating a sharp, well-defined shadow (umbra) without a penumbra.
• A penumbra forms only when light comes from an extended source, allowing some light to partially enter the shadowed area.

6. Answer the following questions in your own words:

(a) What is meant by scattering of light?

→ Scattering of light occurs when light rays hit tiny particles in the atmosphere and spread in different directions, causing effects like the blue sky and red sunsets.

(b) Does the shadow really vanish in the zero shadow condition?

→ No, the shadow does not vanish completely. At noon on a zero shadow day, the sun is directly overhead, making the shadow fall directly below the object and appear invisible.

(c) Will the laser beam be seen if it passes through a glass box which contains a lighted incense stick?

→ Yes, the laser beam will be visible because the smoke particles scatter the light, making the beam appear in the air.

7. Discuss and write:

(a) Write a science-based paragraph on ‘What if the sun did not rise?’

→ If the sun did not rise, the earth would be completely dark and cold. Plants would not perform photosynthesis, leading to the death of plants and animals. Human life would also be affected, as there would be no source of heat and energy to sustain life.

(b) What efforts will you make to remove the misconceptions about eclipses?

→ I will educate people about the scientific reasons behind eclipses and explain that they are natural events, not bad omens. I will also encourage safe viewing practices and promote awareness to remove superstitions.

(c) Various eclipses and the conditions during that period.

→ Solar Eclipse: Occurs when the moon comes between the sun and earth, blocking sunlight.→ Lunar Eclipse: Happens when the earth’s shadow falls on the moon, partially or completely covering it.

8. Explain the difference:

(a) Point Sources and Extended Sources of Light

(b) Umbra and Penumbra