An electric kettle has two coils. When one of these is switched on, the water in the kettle boils in 6 minutes. When the other coil is switched on, the water boils in 3 minutes. If the two coils are connected in series, find the time taken to boil the water in the kettle.

Two heater coils separately take 10 minutes and 5 minutes to boil a certain amount of water.Find the time taken by both the coils connected in series to boil the same amount of water.

Two heating coils, one of fine wire and the other of thick wire of the same material and of the same length are connected in series and in parallel. Which of the following statement is correct ?

Two pipes running together can fill cistern in 6 minutes. One pipe takes 5 minutes more than the other to fill the cistern, find the time in which each pipe would fill the cistern.

In an ordinary electric heater, if the length of the coil is reduced to half, a given quantity of water will boil in

A small retangular coil ABCD contains 140 turns of wire. The sides AB and BC of the coil are of length 4.5 and 2.8 cm respectively, as shown in the figure The coil is held between the poles of a large magnet so that the coil can rotate about an axis thorugh its centre. The magnet produces a uniform magnetic field of flux density B between its poles. When the current in the coil is 170 mA, the maximum torque produced in the coil is 2.1 xx 10^-3 N m . The current in the coil in (a) is switched off and the coil s positioned as shown in the figure. The coil is then turned thorugh an angle of 90^@ in a time of 0.14 s. Calculate the average e.m.f. induced in the coil.

An electric kettle takes 4 A current at 220 V. How much time will it take to boil 1 kg of water from temperature 20^(@)C ? The temperature of boiling water is 100^(@)C

One day in the morning, Ramesh filled up 1/3 bucket of hot water from geyser, to take bath. Remaining 2.3 was to be filled by cold water (at room temperature) to bring mixture to a comfortable temperature. Suddenly Ramesh had to attend to something which would take some time say 5 - 10 minutes before he could take bath. Now the he had two options: (i) fill the remaining bucket completely by cold water and then attend to the work, (ii) first attend to the work and fill the remaining bucket just before taking bath. Which option do you think would have kept water warmer ? Explain.