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A moving test charge experiences a force in addition to the gravitational and electric forces, which is called the magnetic force. It is described by a field called the magnetic field.

All magnets have an invisible magnetic field around them. It is a vector quantity represented by the symbol B. Its SI unit is the tesla.

Oersted demonstrated that a current carrying conductor creates a magnetic field in the surrounding space. The strength of the magnetic field decreases with distance.

The magnetic field is defined via a magnetic force "F" acting on a test charge "Q" moving with the velocity "v" in a magnetic field "B". Magnetic force is the cross-product of the velocity vector and the magnetic field vector.

The direction of the magnetic force can be determined using the right-hand rule.

If the fingers pointing in the direction of velocity are curled towards the direction of the magnetic field, then the thumb represents the magnetic force direction.

The vector sum of the electric and magnetic forces is called the Lorentz force.