In case of a fire, before the fire men use the water, they shut off the main electrical supply for the area. Explain why they do this? `(AS_(1))`

Why the fire brigade start the work by putting off the electric mains?

Water is not used to control fires involving electrical equipment.Why?

Two vessels have the same area but different shapes. The first shapes takes twice the volume of water that the second vessel requires to fill up to a particular common height? Is the force exerted by the water on the base of the vessel the same in the two cases? If so, why do the vessels filled with water to that same height give different readings on a weighing scale?

Explain the following. (a) Why is the tungsten used almost exclusively for filament of electric lamps? (b) Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal? (c) Why is the series arrangement not used for domestic circuits? (d) How does the resistance of a wire vary with its area of cross-section? (e) Why are copper and aluminium wires usually employed for electricity transmission?

Explain why (a) Two bodies at different temperatures T_(1) and T_(2) if brought in thermal contact do not necessarily settle to the mean temperature (T_(1) + T_(2))//2 . (b) The coolant in a chemical or a nuclear plant (i.e., the liquid used to prevent the different parts of a plant from getting too hot) should have high specific heat. (c) Air pressure in a car tyre increases during driving. (d) The climate of a harbour town is more temperate than that of a town in a desert at the same latitude.

Saline hydrides are known to react with water violently producing fire. Can CO_(2) , a well known fire extinguisher, be used in this case? Explain.