Heat | Science | Chapter 4 | Class 7th | Questions and Answers |

JANDKNCERT | Science | Class 7th |

Heat | Science | Chapter 4 | Class 7th | Questions and Answers |

 

Chapter 4: Heat

Q1. State similarities and differences between the laboratory thermometer and the clinical thermometer.

Ans. Similarities between Clinical Thermometer and Laboratory Thermometer:

(i). Both the thermometers are used to measure temperature.

(ii). Both consist of the uniform glass tubes.

(iii). Both use a scale to read the temperature.

(iv). Both the thermometers have a bulb filled with mercury.

(v). Both have a shining thread connected to the mercury.

Differences between Clinical Thermometer and Laboratory Thermometer:

 

Clinical Thermometer	Laboratory Thermometer
i. It measures the body temperature.	i. It measures the temperature of other objects.
ii. Its scale ranges from 350C to 420C.	ii. Its scale ranges from -100C to 1100C.
iii. It is short in length.	iii. It is long in length.

 

 

Q2. Give two examples of each of the conductors and insulators of heat.

Ans.

Example of Conductors: Aluminium, iron, copper

Example of Insulators: Plastic, wood, rubber

Q3. Fill in the blanks:

(a) The hotness of an object is determined by its __________.

(b) Temperature of boiling water cannot be measured by a _____________ thermometer.

(c) Temperature is measured in degree ______________.

(d) No medium is required for transfer of heat by the process of __________.

(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of ______________.

(f) Clothes of ______________ colours absorb heat better than clothes of light colours.

 

Ans.

(a) The hotness of an object is determined by its temperature.

(b) The temperature of boiling water cannot be measured by a clinical thermometer.

(c) Temperature is measured in degrees Celsius.

(d) No medium is required for transfer of heat by the process of radiation.

(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of conduction.

(f) Clothes of dark colours absorb heat better than clothes of light colours.

 

Q4. Match the following:

 

(i) The land breeze blows during	(a) summer
(ii) The sea breeze blows during	(b) winter
(iii) Dark coloured clothes are preferred during	(c) day
(iv) Light coloured clothes are preferred during	(d) night

 

Ans.

 

(i) The land breeze blows during	(d) night
(ii) The sea breeze blows during	(c) day
(iii) Dark coloured clothes are preferred during	(b) winter
(iv) Light coloured clothes are preferred during	(a) summer

Q5. Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.

Ans. During winters, wearing more layers of clothing keep us warmer due to a lot of space between these layers as air acts as an insulator between heat and cold and prevents the heat from escaping to the surroundings.

Q6. Look at Fig. 4.13. Mark where the heat is being transferred by conduction, by convection and by radiation.

 

Ans.

 

Q7. In places of the hot climate, it is advised that the outer walls of houses be painted white. Explain.

Ans. Because most of the heat is reflected by the white colour and it is the poor absorber of the heat that keeps the house cool during the day time that is why in hot climate it is advised that the outer walls of houses be painted as white.

Q8. One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be

(a) 80°C      (b) more than 50°C but less than 80°C

(c) 20°C      (d) between 30°C and 50°C

Ans. (c) between 30°C and 50°C, because hot water loses the heat and simultaneously cold water gains the heat.

Q9. An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will…...

(a) flow from iron ball to water.

(b) not flow from iron ball to water or from water to iron ball.

(c) flow from water to iron ball.

(d) increase the temperature of both.

Ans. (b) not flow from iron ball to water or from water to iron ball, because both of them, have the same temperature.

Q10. A wooden spoon is dipped in a cup of ice cream. Its other end…….

(a) becomes cold by the process of conduction.

(b) becomes cold by the process of convection.

(c) becomes cold by the process of radiation.

(d) does not become cold.

Ans. (d) does not become cold, because wood is an insulator of heat.

Q11. Stainless steel pans are usually provided with copper bottoms. The reason for this could be that

(a) the copper bottom makes the pan more durable.

(b) such pans appear colourful.

(c) copper is a better conductor of heat than stainless steel.

(d) copper is easier to clean than stainless steel.

Ans. (c) copper is a better conductor of heat than stainless steel.

 

BOOST YOUR KNOWLEDGE

 

Also Read: General Knowledge for You

1.     Temperature is a measure of the degree of hotness or coldness of an object.
2.     Temperature is measured by a device called a thermometer.
3.     Clinical thermometer is used to measure the temperature of our body.
4.     Average body temperature of a normal person is 37°C.
5.     Laboratory thermometer is used to measure the temperature of objects ranging from -10°C to 110°C.
6.     The transfer or flow of heat from a body at a higher temperature to a body at a lower temperature takes place by the processes of Conduction, Convection, and Radiation.
7.     The process by which heat is transferred from the hotter end to the colder end of an object is known as Conduction.
8.     The process by which heat is transferred by the bulk movement of molecules in liquids or gases is known as Convection.
9.     The process by which the heat is transferred in the form of electromagnetic waves to its surroundings without any medium is called Radiation.
10. The materials that allow heat to pass through them easily are called Conductors.

11. The materials that do not allow heat to pass through them are called Insulators.