CBSE Class 10 Answered

a) A small aluminium rod is suspended horizontally from a stand using two connecting wires. Place a strong horseshoe magnet in such a way that the rod lies between the two poles with the magnetic field directed upwards. For this, put the north pole of the magnet vertically below and south pole vertically above the aluminium rod. Connect the aluminium rod in series with a battery, a key and a rheostat. Pass a current through the aluminium rod from one end to other (B to A). The rod is displaced towards left. The displacement of the rod in the above activity suggests that aforce is exerted on the current-carrying aluminium rod when it is placed in a magnetic field.

Now change the direction of field to vertically downwards byinterchanging the two poles of the magnet. It is once again observed that the direction of force acting on the current-carrying rod gets reversed.

It shows that the direction of the force on the conductor depends upon the direction of current and the direction of the magnetic field. 

Experimentshave shown that the displacement of the rod is largest (or the magnitudeof the force is the highest) when the direction of current

is at right angles to the direction of the magnetic field.

So, if the direction of magnetic field and direction of current are perpendicular to each other the force experienced will be more. It can be determined

by the magnitude of displacement of the rod.