Which instrument is used to convert electrical energy into mechanical energy?

You have just paid the electricity bill for your house.
$(i)$ What was it that your family consumed,for which you had to pay?
$(ii)$ In what unit was it measured?

An alternating electric current has a frequency of $50 \, Hz$. How many times does it change its direction in one second? Give reason for your answer.

What is short-circuiting in an electric supply?

Which rule is used to determine the direction of induced current in a circuit?

The figure shows a long solenoid,a cylindrical coil of a number of turns of insulated copper wire,connected to a battery through an ammeter $A$ and a rheostat $Rh$.
$(i)$ Which end of the solenoid is a $N$-pole and which end is a $S$-pole?
$(ii)$ Draw the magnetic field lines inside the solenoid and indicate their directions. Are magnetic field lines closed?
$(iii)$ How can you increase the strength of the magnetic field inside the solenoid? Give two methods.