CBSE Class 10 Science 2020 · Paper 31(B) · Question 23

A solenoid is a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. Inside a current-carrying solenoid the field lines are parallel straight lines, so the magnetic field is the same at all points inside it: the field inside the solenoid is uniform. (Outside, its field is like that of a bar magnet, with a north pole at one end and a south pole at the other.) This strong field can be used to magnetise a piece of magnetic material, such as soft iron, placed inside the coil. The soft-iron core becomes a magnet while the current flows, and the magnet so formed is called an electromagnet.