NCERT Solutions Class 7 Science
The NCERT Solutions in English Language for Class 7 Science Chapter – 4 (Heat) has been provided here to help the students in solving the questions from this exercise.
Chapter – 4 (Heat)
1. State similarities and differences between the laboratory thermometer and the clinical thermometer.
Answer –
Similarities
- Both are made of glass and consist of long narrow glass tube.
- At one end both of them have a bulb.
- Bulbs of both the thermometers consist of mercury
- Celsius scale is present in both the thermometer
Differences
| Clinical Thermometer | Laboratory thermometer |
| Temperature range if 35 to 42 0 c | Temperature range is -10 to 110 0 c |
| Used to measure human body temperature | Used to measure temperature in the laboratory |
| It has kink which prevents immediate backflow of mercury | It does not have a kink |
2. Give two examples each of conductors and insulators of heat.
Answer –
Conductors – Iron and Copper
Insulators – Plastic and wood
3. 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. Heat is transferred to its other end by the process of ______________.
(f ) Clothes of ______________ colours absorb more heat better than clothes of light colours.
Answer –
(a) The hotness of an object is determined by its temperature.
(b) Temperature of boiling water cannot be measured by a clinical thermometer.
(c) Temperature is measured in degree Celcius.
(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. Heat is transferred to its other end by the process of conduction.
(f) Clothes of dark colours absorb more heat better than clothes of light colours.
4. Match the following :
| Column-I | Column-II |
| (i) Land breeze blows during | (a) summer |
| (ii) Sea breeze blows during | (b) winter |
| (iii) Dark coloured clothes are preferred during | (c) day |
| (iv) Light coloured clothes are preferred during | (d) night |
Answer –
| Column-I | Column-II |
| (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 |
5. Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.
Answer – More layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing because air gets trapped in-between layer. As air is a bad conductor of heat it does not allow the escape of the heat from the body.
6. Look at Fig. 4.13. Mark where the heat is being transferred by conduction, by convection and by radiation.
Answer –
7. In places of hot climate it is advised that the outer walls of houses be painted white. Explain.
Answer – In places of hot climate, it is advised to paint the outer walls of houses as white because a light colour such as white reflects back most of the heat that falls on it. Hence, a light colour tends to keep the house cool.
8. 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
Answer – (d) The temperature of the mixture will be between 30°C and 50°C because hot water loses the heat and simultaneously cold water gains heat
9. 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.
Answer – (b) The heat will not flow from iron ball to water or from water to iron ball as both the substances have
10. 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.
Answer – (d) Its other end does not become cold as wood is a bad conductor of heat.
11. Stainless steel pans are usually provided with copper bottoms. The reason for this could be that
(a) 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.
Answer – (c) copper is a better conductor of heat than the stainless steel.
