21.

An electric heater is rated 1000 W – 200. Calculate:

i) the resistance of the heating element.

ii) the current flowing through it. 

i) Give two characteristics properties of copper wire which make it unsuitable for use as a fuse wire.

i) The diagram (a) and (b) given below are a plug and a socket, with arrow marked as 1,2,3, and 4,5, respectively on them. Identify and write live (L), Neutral (N) and Earth (E) against the correct number. 

Calculate the electrical energy consumed when a bulb of 40 W is used for 12.5 hours every day for 30 days. 

The figure given below shows an electromagnet.

i) What will be the polarity at the end X?

Why do pieces of ice added to a drink cool it much faster than ice cold water added to it? 

4 g of water at 60^o C is poured into a vessel containing 50 g of water at 20^o C. The final temperature recorded is 30^o C. Calculate the thermal capacity of the vessel.

State in brief, the meaning of each of the following:

i) The heat capacity of a body is 50 J^o C^-1.

ii) The specific latent heat of fusion of ice is 336000 J kg^-1.

i) What is the principle of method of mixtures?

Calculate the amount of ice which is required to cool 150 g of water contained in a vessel of mass 100 g at 30^o C, such that the final temperature of the mixture is 5^o C. Take specific heat capacity of material of vessel as 0.4 Jg^-1o C^-1, specific latent heat of fusion of ice = 336 Jg^-1, specific heat capacity of water = 4.2 J g^-1o C^-1