When a material is placed inside a coil carrying current (may be solenoid) it will get magnetised. A bunch of nails or an iron rod placed along the axis of the coil can be magnetised by the current allowed to pass through the coil.

Once the current is put-off the magnetic field will also be lost. Such magnets are called electromagnets.

Properties of magnetic field lines:
The magnetic field lines have the following properties:
(i) They originate from North pole of a magnet and end at its South pole, by convention.
(ii) These lines are closed and continuous curves.
(iii) They are crowded near the poles, where the magnetic field is strong and separated far from the poles, where the magnetic field is weak.
(iv) Field lines never intersect with each other. If they do, that would mean that there are two directions of the magnetic field at the point of intersection, which is impossible.

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.

An earth wire is connected to the metallic body of the appliances. This provides a low resistance conducting path for current and any leakage is safely conducted to earth reducing the severity of electric shock.

(a)  (i) It is used in cranes for lifting heavy loads.
      (ii) used in electric bells.
 (b)  Loudspeakers, Galvanometer, voltmeter.

Electric fuse is used for protecting the circuits due to short circuiting or overloading of the circuits.

The magnetic field produced by a solenoid is similar to the bar magnet.

The magnetic field lines around a straight conductor carrying current are concentric circles.

It is a vector quantity as it has both magnitude and direction.

(a) By permanent magnet
(b) By electromagnet
(c) By current carrying conductors