Question

What is the direction of the magnetic field that produces the magnetic force on a positive charge as shown in each of the three cases in the figure below, assuming B is perpendicular to v?

Short answer

(a) The direction of the magnetic field will be to the inwards (into the page).

(b) The direction of the magnetic field will be toward the left

(c) The direction of the magnetic field will be outwards (out of the page)

Step-by-step solution

Definition of magnetic force.

A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials.

Explanation of the direction of the magnetic field.

(a)

By having the force pointing towards the left and the velocity pointing upwards, the magnetic field for a positive charge will be given with Fleming’s right-hand rule, where the thumb points towards force, the forefinger points to the direction of velocity then the middle finger gives the direction of the magnetic field. Therefore the direction of the magnetic field is inwards (into the page).

(b)

By having the force pointing inwards (into the page) and the velocity pointing downwards then the magnetic field direction will be towards the left using Fleming’s right-hand rule.

(c)

By having the force pointing upwards and the velocity pointing towards the left then the magnetic field direction will be outwards (out of the page) to the left using Fleming’s right-hand rule.