NCERT 7th Class (CBSE) Science: Heat and Temperature

Question: What is land and sea breeze explain?

Answer: During the day, the land gets heated faster than the water. The air over the land becomes hotter and rises up. The cooler air from the sea rushes in towards  the land to take its place. The warm air from the land moves towards the sea to complete the cycle. The air from the sea is called the sea breeze.

At night, the water cools down more slowly than the land. So, the cool air from the land moves towards the sea. This is called the land breeze

Question: How does the heat from the sun reach us?

Answer: It cannot reach us by conduction or convection as there is no medium such as air in most part of the space between the earth and the sun. From the sun the heat comes to us by  another process known as radiation. Radiation can take place whether a medium is present or  not.

Question: In summer we prefer light-coloured clothes and in winter we usually wear dark-coloured clothes. Why

Answer: Dark surfaces absorb more heat and, therefore, we feel comfortable with dark coloured clothes in the winter. Light coloured clothes reflect most of the heat that falls on them and, therefore, we feel more comfortable wearing them in the summer.

Question: How Woolen clothes keep us warm in winter?

Answer: Woolen clothes keep us warm during winters because wool is a poor conductor of heat and it has air trapped in between the fibres.

Question: Why one thick blanket  is less warm up than  two thin blankets joined together?

Answer: There is a layer of air in between the blankets. Since air is bad conductor of heat prevent body heat to escape out.

Question: How is heat transferred in solids, liquids and gases?

Answer: The heat flows from a body at a higher temperature to a body at a lower temperature. In solids, generally, the heat is transferred by conduction. In liquids and gases the heat is transferred by convection. No medium is required for transfer of heat by radiation.

Question: Why we wear light cloths in summer?

Answer: Dark-coloured objects absorb radiation better than the light-coloured  objects. That is the reason we feel more comfortable in light-coloured clothes in the summer.