Chapter 1 Physical Environment Answer in One or Two sentences
Question 1. What do you mean by 1 calorie?
Answer:
1 Calorie:-
This is the amount of heat required to increase the temperature of g of pure water by 1°C.
Question 2. What is meant by the specific heat of a substance?
Answer:
Specific heat of a substance:-
Specific heat of a substance is defined as the amount of heat required to raise the temperature of a unit mass of substance byl°C.
Question 3. What is the unit of specific heat in the SI unit?
Answer:
Specific heat of a substance:
The unit of specific heat is Joule per kilogram per degree centigrade (J/kg °C).
Question 4. Name two substances that do not have fixed melting points.
Answer:
The substances which do not have fixed melting points are wax, butter, etc.
Question 5. Give an example of one substance that increases in volume when it melts.
Answer:
When solid wax melts, its volume increases.
WBBSE Class 8 Heat concise answer questions
Question 6. What happens to the melting point of ice when pressure is increased?
Answer:
When pressure is increased, the melting point of ice is decreased.
Question 7. What do you mean by freezing mixture? When salt is mixed with ice, its temperature decreases.
Answer:
Freezing Mixture:-
This mixture is called a freezing mixture. For example, when ice and common salt is mixed in a 3:1 weight ratio, the temperature becomes approximately – 23°C. This is a freezing mixture.
Question 8. What happens to the melting point of wax if pressure is increased?
Answer:
The melting point of wax increases when pressure is increased.
Question 9. What do you mean by the latent heat of vaporization?
Answer:
latent heat of vaporization:-
Latent heat of vaporization is the quantity of heat absorbed by a substance of unit mass when it undergoes a change of state from liquid to vapor at a particular temperature.
Question 10. What do you mean by the boiling point of a liquid?
Answer:
The boiling point of a liquid:-
At a particular pressure boiling point of a liquid is the temperature at which the boiling starts and the temperature remains constant till all the liquid is vaporized.
Read And Learn More WBBSE Solutions For Class 8 School Science Very Short Answer Type Questions
Question 11. If some salt is dissolved in water, how it will affect the boiling point of water?
Answer:
When some salt is dissolved in water, its boiling point will increase.
Question 12. What should be the characteristic property of a fuse wire and why?
Answer:
The fuse wire should be made up of a low-melting solid. When a large amount of electricity suddenly flows through it,
heat is produced and the wire melts easily at lower temperatures, thereby preventing further passage of electricity through it and thus protecting the costly and important electrical instruments and gadgets.
Question 13. What is the process of transfer of heat within a solid substance?
Answer:
Heat is transferred within a solid substance from one part to another by conduction.
Question 14. How heat is transferred from the sun to the earth?
Answer:
Heat is transferred from the sun to the earth by radiation.
Very short answer questions on heat for Class 8
Question 15. Among the different processes for the transfer of heat, which one is the fastest?
Answer:
Radiation is the fastest of the three processes by which heat is transferred.
Question 16. In the thermos-flask, the region between two glass walls is evacuated. Why?
Answer:
The region between two glass walls is evacuated, this means that there is no medium.
That way, the chances of loss of heat from inside the flask to the outside are minimized by eliminating the possibility of heat transfer by conduction and convection. Both these processes require a medium for the transfer of heat.
Question 17. What are the magnitude of the latent heat of the vaporization of water (at 100°C and 1 atmospheric pressure) and the latent heat of fusion of ice (at 0°C and 1 atmospheric pressure)?
Answer:
The latent heat of the vaporization of water is 537 calories per gram per degree centigrade and the latent heat of the fusion of ice is 80 calories per gram per degree centigrade (at 0°C and 1 atmospheric pressure).
Question 18. Ame is two substances that do not melt when they are heated.
Answer:
Iodine and camphor are the two solid substances (at room temperature) which, when heated, are directly converted to vapor i.e. undergo sublimation without melting.
WBBSE Class 8 Science practice concise answers questions on heat
Question 19. Compute the temperature rise that would take place when 100 cal of heat is supplied to 5g of water.
Answer:
We know, H = m x s x (t2-t1).
Here, H = 100 cal, m = 5g, s = 1 cal/g. °C.
∴t2-t1=H/m xs =100/5×1=20°c
∴Rise in temperature = 20°C.
Question 20. What happens due to the exchange of latent heat?
Answer:
Change of state of matter without temperature change.
Question 21. In which type of heat transfer method particles of the medium are displaced?
Answer:
Convection (by establishing convection current).
Question 22. If Y cal of heat is required to raise the temperature of Xg of mass by 1°C, then what is the specific heat of the material?
Answer:
From H = m x s x t, we have s = H/mxt where t=(t2-t1)
Putting the values of H = Y cal, m =Xg and t = 1°C,
Specific heat, S= Y/x.1=y/x
WBBSE Chapter 1 heat quick answer solutions
Question 23. Among Digha and Darjeeling, where is the boiling point of water lower?
Answer:
The boiling point of water is lower in Darjeeling since it is a hill station.
Question 24. Which physical quantity determines the flow of heat energy?
Answer:
Temperature of a substance.
Question 25. A metal spoon is placed in one of two identical cups of hot coffee. Why does the cup with the spoon have a lower temperature after a few minutes?
Answer:
Heat energy is removed from coffee mostly by conduction through the spoon. This cannot happen in the other cup.
Heat concepts summary with very short answers for Class 8
Question 26. On a bright sunny day, a boy standing on a seashore is flying a kite. In which direction will the kite fly?
Answer:
The hot air of land will take the kite towards the sea.
Question 27. Which of the following is a better reflector of heat and which one is a better absorber of heat? 1. Dull black surface 2. Shiny white surface.
Answer:
- Dull black surface: better absorber of heat
- Shiny white surface: better reflector of heat.