Page 42 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

For example, heating water in a pot on the stove causes the water at the bottom to

heat up and rise, while cooler water near the surface sinks and replaces it.
4. Write the steps of using a clinical thermometer.

Ans. Steps of using a clinical thermometer:
• Before using the thermometer, wash it properly with an antiseptic solution.

• Check to see if the level of mercury is below 35°C. If not, then give it a few

jerks.
• Place the bulb of the thermometer under the tongue for a minute. Take it out

and read the temperature by keeping the level of mercury at eye level. Ensure
that you don’t touch the bulb while reading the temperature.

• Wash the thermometer again after use.
5. Why do we wear light-coloured clothes in summer and dark-coloured clothes in

winter?

Ans. We wear light-coloured clothes in summer because they reflect more sunlight and
heat, helping to keep our body cool. Light colours absorb less heat and allow more of

the Sun’s energy to be reflected away from the body, reducing heat absorption and
keeping us comfortable in hot weather.

Conversely, we wear dark-coloured clothes in winter because they absorb more
sunlight and heat. This helps to keep our body warmer by trapping heat close to

the skin. Dark colours absorb sunlight more effectively, which is beneficial in colder

weather when we want to retain body heat and stay warm.
6. Explain any two examples of radiation.

Ans. Two examples of radiation are explained below:
(a) Sunlight and Earth’s surface: Radiation from the Sun is essential for life on Earth.

Sunlight reaches from the Sun to the Earth via radiation. When sunlight reaches
the Earth’s surface, it warms the land, water bodies and the atmosphere.

Objects and living things exposed to sunlight absorb this heat energy, causing

them to warm up. For example, on a sunny day, when we step outside, we can
feel the warmth of the Sun’s rays on our skin.

(b) Heat from a fire: Another example of radiation is the heat emitted from a fire or
a hot object. When an object is heated to a high temperature, it starts radiating

(emits radiation). This radiation is not visible to the human eye but can be felt as
heat. For example, when we stand near a campfire or a fireplace we feel warm.

This is because the heat from the fire travels through the air via radiation,
warming our skin and clothing.

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