Question

describe an experiment to show that a magnetic field exert a force on a current carrying wire

Answer 1

Take a small aluminium rod AB. Using two connecting wires suspend suspend it with the help of an iron stand as shown in the Fig. 13.46. Place this sluminium suspended rod in the magnetic field of horse shoe magnet in such a way that its field is directed upwards. 

A current carrying rod, AB, experiences a force perpendicular to its length and the magnetic field connect the aluminium  rod in an electric circuit having battery, key and rheostat. 

Pass the current from the aluminium rod from its end B to A. 

You will observe that the rod is displaced towards the left, i.e., towards the inward of the magnet. 

If the direction of current is reversed through the rod, then it is observed that the direction of displacement of the rod is also reversed. Now it will more towards the right. 

The displacement of the rod in the above activity suggests that a force is exerted on the current carrying conductor, when it is placed in a magnetic field. The direction of this force is given by Fleming's left hand rule. 

According to Fleming's left hand rule, stretch the thumb, forefinger and central finger of your left hand such that they are mutually perpendicular. If the fore finger points in the direction of magnetic field and the central in the direction of current, then the thumb will point in the direction of motion or force acting on the conductor. The direction of force acting on a current carrying wire placed in the magnetic field is (i) perpendicular in the direction of current, and (2) perpendicular to the direction of magnetic field.