A resistance R is connected across the terminal of an electric cell of internal resistance 2Ω and the voltage was reduced to 3/5 of its nominal value.
The value of R is

A student is at a height 4m above the ground during a thunderstorm. Give that the potential difference between the thundercloud and the ground is 10⁷v, the electric field created by the storm is

A working electric motor takes a current of 1.5 A when the p.d across it is 250V. If its efficiency is 80%, the power output is

In a Daniel cell, the depolarizer, positive and negative electrodes are respectively