When the magnetic field and the direction of current are perpendicular to each other, the deflection is maximum. But when they are in the same plane, no deflection takes place. So, the current carrying conductor needs to be placed in the same plane as the magnetic compass to attain no deflection.

The time period (T) of one cycle would be = 
2 X (0.05 s) = 0.1 s.
Frequency, f = 1/t.
Hence, f= (1/0.1) = 10 Hz.

The factors on which force produced due to magnetic field depends are:
(i) length of the conductor.
(ii) the amount of current flowing.
(iii) The strength of magnetic field.
(iv) direction of current and magnetic field.
If are at right angles, then maximum amount of force will be produced.

An electric motor.

When the total current drawn by all the appliances at a particular time exceeds the bearing capacity of that wire, the wires of the domestic wiring gets heated. This is called overloading.

We know that for making an electromagnet we need to place a soft iron core inside a solenoid. Soft iron is a ferro-magnetic material and hence it augments the magnetic property of solenoid by thousands of times. Thus, for making a permanent electromagnet, we need to place a soft iron core inside a solenoid.

(a) When we magnetise a piece of magnetic material such as soft iron by keeping it inside a coil and then passing current through it, the magnet so formed is called electromagnet.
(b) (i) Steel is used to make permanent magnet.
(ii) Soft iron is used to make temporary magnets.
(c) Take a coil of wire having N number of turns and then wound it around a soft iron core. Connect the end of the wire with a battery and plug key and then let current pass through the coil. While current is passing through the coil, bring a compass near the coil. It will be observed that compass needle shows deflection. This shows that the coil will have a magnetic field of its own. The magnet so formed is called an electromagnet.