21.

i) A substance has nearly zero resistance at a temperature of 1 K. What is such a substance called?

ii) State any two factors which affect the resistance of a metallic wire. 

i) Which part of an electrical appliance is earthed. 

State a relation between electrical power, resistance and potential difference in an electrical circuit. 

i) In what unit does the domestic electric metre measure the electrical energy consumed? State the value of this unit in S.I. unit.

ii)Why should switches be always connected to the live wire.

i) Which material is the calorimeter commonly made of?

i) Define the term ‘specific latent heat of fusion’ of a substance.

ii) Name the liquid, which has the highest specific heat capacity.

iii) Name two factors on which the heat absorbed or given out by a body depends.

i) An equal quantity of heat is supplied to two substances A and B. The substance A shows a greater rise in temperature. What can you say about the heat capacity of A as compared to that of B?

ii) What energy change would you expect to take place in the molecules of a substance when it undergoes?

1. A change in its temperature.

2. A change in the state without any change in its temperature?

50 g of ice at 0^o C is added to 300 g of a liquid at 30^o C. What will be the final temperature of the mixture when all the ice has melted? The specific heat capacity of the liquid is 2.65 Jg^-1oC^-1 while that of water is 4.2 J g^-1o C^-1. Specific latent heat of fusion of ice = 336 J g^-1.

Give two differences between a d.c. motor and an a.c generator. 

A device is used to transform 12 V a.c. to 200 V a.c.

i) What is the name of this device?

ii) Name the principle on which it works.