NCERT Solution class 7 Science Chapter-4

Chapter – 4           Heat

Chapter Exercises

Page no. – (45)

 

Q.1- State similarities and differences between the laboratory thermometry and the clinical thermometer.

Ans.1- Similarities:-

1. Both have bulb.
2. Both contain mercury in bulb.

• Both are made of glass and consist of long narrow glass tube.

1. Both use celsius scale on the glass tube.

Differences:-

Clinical Thermometer	Laboratory Thermometer
Temperature range 35° to 42°C	Temperature range -10° to 110°C
Measure human body temperature	Measure temperature in laboratory

 

Q.2- Give two examples each of conductors and insulators of heat.

Ans.2- Conductor – Iron and Steal.

Insulator – Plastic and Rubber.

 

Q.3- Fill in the blanks:-

1. The hotness of an object is determined by its ____.
2. Temperature of boiling water cannot be measured by a ____ thermometer.
3. Temperature is measured in degree ____.
4. No medium is required for transfer of heat by the process of ____.

• A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of ____.

1. Clothes of ____ colour absorb more heat better than clothes of light colours.

 

Ans.3-

1. The hotness of an object is determined by its __temperature__.
2. Temperature of boiling water cannot be measured by a __clinical__
3. Temperature is measured in degree __celcius__.
4. No medium is required for transfer of heat by the process of __radiation__.

• A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of __conduction__.

1. Clothes of __dark__ colour absorb more heat better than clothes of light colours.

 

Q.4- Match the following:-

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

 

Ans.4-

i.	Land breeze blows during	d.	Night
ii.	Sea breeze blows during	c.	Day
iii.	Dark coloured clothes are preferred during	b.	Winter
iv.	Light coloured clothes are preferred during	a.	Summer

 

Q.5- Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing?

Ans.5- More layers of clothing keep us warm in winters as they have a lot of space between them. This space gets filled up with air. Air is a bad conductor, it does not allow the body heat to escape out.

 

Q.6- Look at figure 4.6. Mark where the heat is being transferred by conduction, by convection and by radiation.

Ans.6-

Q.7- In place of hot climate it is advised that the outer walls of houses be painted white. Explain.

Ans.7- In places of hot climate, it is advised that the outer wall of houses be painted white because white colour reflects heat and the houses do not heat up too much and keeping house cool.

 

Q.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

1. 80°C
2. More than 50°C but less than 80° C
3. 20°C
4. Between 30°C and 50°C

Ans.8- d) Between 30°C and 50°C.

 

Q.9- An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will:-

1. Flow from iron ball to water.
2. Not flow from iron ball to water or from water to iron ball.
3. Flow from water to iron ball.
4. Increase the temperature of both.

Ans.9- b) Not flow from iron ball to water or from water to iron ball.

 

Q.10- A wooden spoon is dipped in a cup of ice –   cream. Its other end:-

1. becomes cold by the process of conduction.
2. becomes cold by the process of convectio.
3. becomes cold by the process of radiation.
4. does not become cold.

Ans.10- d) does not become cold.

 

Q.11- Stainless steel pans are usually provided with copper bottoms. The reason for this could be that:-

1. Copper bottom makes the pan more durable.
2. Such pans appear colourful.
3. Copper is a better conductor of heat than the stainless steel.
4. Copper is easier to clean than the stainless steel.

Ans11.- c) Copper is a better conductor of heat than the stainless steel.