Oersted's experiment shows that a current carrying wire exerts a force on a magnetic needle and deflects it from its usual north-south position. The reverse must also be true, which was proved by the French scientist Andre Marie Ampere, who suggested that a magnet must also exert an equal and opposite force on the current carrying conductor. The above mentioned concept can be best understood by way of a demonstration as explained below.
| Procedure | Observation |
| A small aluminium rod AB (5 cm in length) is connected to the wires and suspended horizontally as shown in the fig | |
| A strong horse-shoe magnet is placed in such a way that the magnetic field is directly upwards and is placed vertically | The rod AB gets displaced. |
| The rod AB is connected in series to a battery, a key and a rheostat | |
| Switch on the current |
| Procedure | Observation |
| Repeat the experiment by changing the direction of flow of current. | The rod AB gets displaced in the reverse direction. |
| Procedure | Observation |
| Repeat the experiment by reversing the direction of magnetic field. | The rod AB gets displaced in the reverse direction. |
Inference
A current carrying conductor experiences a force when placed in a magnetic field. The direction of force is reversed when the direction of current in the conductor is reversed.
Fleming's left Hand Rule
Fleming's left hand rule helps us to predict the movement of a current carrying conductor placed in a magnetic field.
According to this rule, extend the thumb, forefinger, and the middle finger of the left hand in such a way that all the three are mutually perpendicular to each another. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, then, the thumb points in the direction of the force exerted on the conductor.
Devices that use current carrying conductors and magnetic fields include electric motors, generators, loudspeakers and microphones.