Page 41 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

The reverse process takes place at night. The land cools down faster than sea. The
air above the sea is warmer than the air above the land. The warm air above the sea

being lighter rises up. Cool air from the land rushes in towards the sea to occupy the
space left by the warm air. The flow of air from the land towards the sea is known as

land breeze.
2. Give reasons for the following.

(a) It is advisable to place room heaters at the ground level for effective heating.
Ans. It is advisable to place room heaters at ground level ensuring efficient heating by

allowing warm air to rise naturally and circulate evenly throughout the room via
convection. This positioning also enhances safety, reducing the risk of accidential

contact or burns, particularly in households with children or pets.
(b) Ventillators should be installed near the ceiling.

Ans. Ventilators are typically installed near the ceiling to effectively exhaust warm air and
moisture that naturally rises due to convection. This placement ensures efficient

ventilation by allowing the higher, warmer air to be expelled out of the room, while
cooler air is drawn in to replace it. Additionally, installing ventillators near the ceiling

helps to prevent the accumulation of stagnant air, odours and moisture, promoting

better air circulation.
3. Differentiate between convection and conduction.

Ans. Conduction involves the transfer of heat through direct contact between particles or
objects. In this process, heat energy flows from areas of higher temperature to lower

temperature through the collisions of particles of the solid. There is no movement of
the particles in conduction. It occurs in solids, where the particles are closely packed.

For example, when we touch a hot utensil, heat is transferred to our hand through

conduction.
Convection occurs in liquids and gases. In convection, the molecules of liquids and

gases travel with heat energy from a hotter region to a cooler region, creating a
circular flow. It occurs in liquids and gases where particles are more free to move.

41