CBSE Class 10 Science 2020 · Paper 31/C/3 · Question 24

Solenoid: a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. Field lines (see the figure): the pattern is that of a bar magnet. Inside the coil the lines are straight, parallel and equally spaced, running from the S end to the N end; outside they leave the N end, curve round and enter the S end. Every line is a closed loop and no two lines cross. Inside: the parallel, equally spaced lines indicate that the magnetic field is the same at all points inside the solenoid, that is, the field is uniform. Use: the strong field inside can magnetise a piece of magnetic material such as soft iron placed in the coil, making an electromagnet.