An electron moves north at a velocity of 4.5 × 104 m/s and has a magnetic force of 7.2 × 10-18 n exerted on it. if the magnetic field points upward, what is the magnitude of the magnetic field? use 1.60 × 10–19 c for the magnitude of the charge of an electron

The magnetic force on a moving charge is given by:

where q is the charge, v is the speed of the charge, B is the magnetic field intensity and is the angle between the directions of B and v.

In our problem, the charge is an electron (), the velocity of the charge is , the magnetic force is and the angle between the direction of v and B is , so and we can ignore the sine in the formula. Therefore, if we rearrange the equation and we put these numbers in, we can find the intensity of the magnetic field: