Chhattisgarh State Board Class 7 Science Chapter 8 Transfer of Heat Exercise Multiple Choice, Questions and Answers here.
(1) Choose the correct options.
(1) The transfer of heat through solids is due to –
(a) Conduction
(b) Convension
(c) Radiation
(d) Due to all above
Answer:- (a) Conduction.
(2) Which is anon conductor/insulator out of these.
(a) Water
(b) Air
(c) Thermocole
(d) All of the above
Answer:- (d) All of the above.
(3) In the following methods of heat transfer the particle of the medium move from one place to another.
(a) Conduction
(b) Convension
(c) Radiation
(d) None of these
Answer:- (b) Convension.
(4) A good absorber of radiation energy is –
(a) Black painted ball
(b) Tin box
(c) White cloth
(d) Iron ball
Answer:- (a) Black painted ball.
(2) Fill in the blanks –
(1) Heat flow by means of ——- is the fastest.
Answer:- Radiation.
(2) There is ——– between the double layer of the thermos flask.
Answer:- Vacuum.
(3) Good emitters of radiation energy are also good ——–.
Answer:- Absorbers.
(4) ——– colour is a good absorber of heat.
Answer:- Dark colour/black.
(5) Both the front surfaces of the double-layered glass bottle inside a thermos flask are painted with white shiny point to prevent heat by ——.
Answer:- Radiation.
(1) Write down the method of heat of heat transfer.
Answer:- Heat can be transfer by following three method.
(i) Conduction-in solid heat transfer through conduction.
(ii) Convension-in convension heat transfer take place due to motion of muscles in liquid or gas.
(iii) Radiation-there is no medium required to heat.
(2) Write down two essential condition for heat transfer by conduction.
Answer:- Condition for heat transfer by conduction are follow.
(i) The objects should be in contact.
(ii) Their temperature should be different
(3) Which materials are conductors of heat? Give any two examples.
Answer:- Conductors – materials that transfer heat through conduction are called conductors. Example-metals, graphite,
(4) Explain conventional currents.
Answer:- The conventional currents move from bottom to top (high to lower region)
Ex – The coldest part of the refrigerator the freezer is in the upper position of the refrigerator so that the air that gets cooled & becomes heavy due to contact with it, start descending to the lower part. These convention currents make the entire air inside the refrigerator cool.
(8) Why are white coloured clothes preferred in summer?
Answer:- During summer wear white-coloured so that the heat absorption is low & do not feel hot. White coloured clothes reflect most of the heat radiations. So, it is comfortable to wear white coloured clothes in summer.
(6) On what conditions does the emitted from hot bodies depend?
Answer:- Conditions for emitted from hot bodies depend on following factor (i) Temperature of the body (ii) Colour of the body (iii) Nature of the surface (smooth or rough)
(5) Solids cannot be heated by convection. Why?
Answer:- In convection heat & transfer takes place due to the motion of muscles. (Higher temperature to lower temperature) but solids molecules are rigid. (They can’t move) So, solids cannot be heated by convection method.
(7) Desert area are very hot in days & very cool at night, why?
We know that good absorbers of energy are also good emitters. At day times sand get hot due to radiation of sun. Sand cannot hold heat energy. At night there is no source of heat. Sand emitted heat energy & become cool. Therefore desert area hot during day time & cool at night.
(9) Why are interiors of solar cookers usually painted black?
Answer:- Interiors of solar cookers usually painted black so, that they can absorb more heat because we know that black colour are good absorbers of heat radiated heat.
