CBSE Class 10 Answered

1. Take a thick straight conductor XY and pass it through the centre of a thick cardboard. 
2. Pass current through the conductor such that it flows from X to Y. 
3. Sprinkle some iron filings on the cardboard and gently tap. You will see that the iron filings arrange themselves in concentric circles around the wire.
4. These concentric circles represent the magnetic field lines. 
5. To know the direction of the magnetic field, we plot the field lines with the help of a compass needle. The North pole of the compass points in the direction of the field at any point. The direction of these field lines is clockwise. 
6. If the direction of current is reversed, these field lines are anticlockwise.

(a) When current is decreased, strength of the field also decreases.

(b) When the current is reversed, the field also gets reversed.