Force on Conductor in Magnetic Field

These notes are based on the chapter Magnetic Effect of Electric current class 10 science NCERT book and CBSE syllabus.

In previous section, you have read that a current carrying conductor exerts a force when a magnet is placed in its vicinity. Similarly, a magnet exerts equal and opposite force on the current carrying conductor.

This was suggested by Andre Marie Ampere, a French Physicist and considered as founder of science of electromagnetism.

The direction of force over the conductor depends on the direction of current. The direction of force over the conductor gets reversed with the change in direction of flow of electric current. It is observed that the magnitude of force is highest when the direction of current is at right angles to the magnetic field.

Fleming's Left Hand Rule

In this figure, you can see that the index finger is showing the direction of magnetic field, middle finger is showing the direction of electric current and thumb is showing the direction of motion because of interaction between magnetic field and electric current.

If direction of electric current is perpendicular to the magnetic field, the direction of force is also perpendicular to both of them.

The Fleming's Left Hand Rule states that if the left hand is stretched in a way that the index finger, the middle finger and the thumb are in mutually perpendicular directions, then the index finger shows the direction of magnetic field and middle finger shows the direction electric current.

Finally, the thumb shows the direction of motion or force acting on the conductor.

The directions of electric current, magnetic field and force are similar to three mutually perpendicular axes, i.e. x, y and z axes.

In this figure, the horizontal axis is showing the direction of force, and vertical axis showing the direction of magnetic field. The third axis is showing the direction of electric current.

This rule explains what happens when a current-carrying conductor is brought into magnetic field of another magnet. You have already read that there is a magnetic field around the current carrying conductor. When the current carrying conductor is brought into a magnetic field, the magnetic fields of the magnet and current carryind conductor interact. This interaction between magnetic fields of two separate objects produces a force. In an electric motor, the shaft rotates due to this force.