a. Longer line in the symbol for a cell represents its positive terminal. A battery has two ends. The longer line represents positive end and the shorter line represents negative end.

b. The combination of two or more cells is called a battery. When two or more cells are combined together, they are known as battery.

c. When current is switched ‘on’ in a room heater, it gets heated. This happens because of heating effects of current.

d. The safety device based on the heating effects of electric current is called a fuse. Using an electric fuse prevents the flow of unduly high electric current and protects the appliances from the damage.