Symbol 'X' indicates the direction of the magnetic field into the page. A straight long wire carrying current along its length is kept perpendicular to the magnetic field. What is the magnitude of force experience by the wire? In what direction does it act?

Since the electric current is due to the charges which are in motion. Hence they must have a velocity let this be the drift velocity ‘V’.

Q = Total charge present on the conductor;

B = Magnetic field;

Magnetic force on the current carrying conductor is given by;

F = BQV. …(1)

Time is taken by the charge to cross the field =‘t’

∵ Velocity =

⇒ V =

Putting V in (1)

F =

F = BiL (∵ I = current = ).

Direction Of Force: By Right-Hand rule

1.) Thumb points in the direction of current (i).

2.) Finger points towards the direction of magnetic field (B).

3.) The thumb gives the direction of the current.

The figure below illustrates the same.

The magnetic field is going inside the paper. Therefore the direction of force is towards left side.