Exercise

I. Choose the correct option to complete each sentence.

1. 

Ans. Region of higher temperature to a reason of lower temperature.

2.

Ans. Total energy of all the moving molecules.

3.

Ans. How hot or cold the water is.

4. 

Ans. Do not conduct heat.

5.

Ans. Poor conductor of heat.

6. 

Ans. Metal in liquid form at room temperature.

II. Fix the true statements and cross the false ones.

1. ✓

2. X

3. ✓

4. X

5. ✓

6. X

III. Answer the following questions in one sentence.

1. What is thermal energy?

Ans. The sum of energy possessed by all the molecules in motion is the thermal energy of the substance.

2. What does temperature of a substance indicate?

Ans. The temperature of a substance indicates the level of thermal energy.

3. Define heat.

Ans. Heat is defined as the thermal energy that flows.

4. Name two good conductors of heat.

Ans. Examples of two good conductors of heat are copper and iron.

5. What are fluids?

Ans. The gases and liquids are called fluids.

6. What is the lower point of an ordinary laboratory thermometer.

Ans. The lower point of an ordinary laboratory thermometer is 0°C.

IV. Answer the following questions in two sentences.

1. How is temperature different from thermal energy?

Ans. The temperature is different from thermal energy. thermal energy is the sum of energy possessed by all the molecules of a substance where is the temperature indicates the level of thermal energy of the substance. In other words the temperature will tell us how hot or cold a substance is.

2. What is a heat insulator?

Ans. the materials like wood plastic which are poor conductors of heat are called heat insulator.

3. How does transfer of heat take place?

Ans. The heat transfers from one place to another bi mainly three ways conduction convection and radiation. The heat transfers from the higher temperature region to a lower temperature region.

4. Why is mercury used in thermometer?

Ans. Mercury is used in thermometer because Mercury being a metal is a good conductor of heat and also it is in liquid form at room temperature as it comes in contact with a hot body it will quickly gains heat and expand due to which it will rise upwards in the capillary tube of thermometer.

5. how does the fur of seals and polar bears help them live in the Arctic regions?

Ans  The fur of seals and polar bear traps the air and forms an excellent heat insulating layer it keeps the animals comfortable one even when the atmospheric temperature drops down very low.

V. Answer the following questions in about four to five sentences.

1. Define the following: conduction, convection, radiation

Ans.

i. Conduction:- it is a process in which heat is transferred from a region of higher temperature to a reason of lower temperature through vibrating molecules.

ii. Convection:- the flow of heat by the movement of the liquid or gas itself from a place of higher temperature to a place of lower temperature is called convection.

iii. Radiation:- it is the mode of transfer of heat where the heat transferring body are not in contract.

2. why does cold water kept in an open container become warm on a hot summer afternoon?

Ans. Cold water kept in an open container becomes warm on a hot summer afternoon this is because the cold water will acquire heat from the warmer surrounding air.

3. Why is the bulb of a thermometer made of thin glass?

Ans. The bulb of thermometer made of thin glass so that transfer of heat between the mercury and its surroundings can take place easily.

4. How does a thermos flask maintain the temperature of liquids kept in it?

Ans. The designing of thermos flask maintain the temperature of liquids kept in. The double walled glass with bacon between the walls reduces the transfer of heat from inside the class as well as outside of it. The silvered surface of the flask reflect the heat rays either trying to enter the flask from outside or leave the flask from inside.

5. How do woolen garments keep us warm?

Ans. The woolen garments have air pockets where air is trapped. being an insulator will not allow the transfer of heat from the body to the surroundings. Moreover wool is a poor conductor of heat so the warmth of the body will not escape and also prevents cold air from reaching the body this is how woolen garments keep the body warm in winter.

6. How do convection currents give rise to Breeze in the coastal region?

Ans. Convection currents give rise to Breeze in coastal region.

During the day the land heats up faster than the sea. So the air above the land becomes warmer and rises upwards and in its place cooler air from above the sea rushes towards the land resulting in a sea breeze during the day.

At night the opposite happens. The land cools faster. Therefore the air above the sea is warmer than the air over the land. At night, cooler air from the land replaces the air above the sea resulting in a land breeze.