Question

A uniform magnetic field exists in a plane pointing from left to right as shown in the figure. In this field, an electron and a proton move vertically as shown. The electron and the proton experience forces:

• A. Both pointing into the plane.
• B. Both pointing out of the plane.
• C. In the direction of magnetic field.
• D. In the opposite direction of magnetic field.

Answer 1

The correct option is A Both pointing into the plane.

Applying Fleming’s left hand rule, holding the forefinger, middle finger, and thumb of the left hand in mutually perpendicular directions, the forefinger indicates the direction of the magnetic field and the middle finger, the direction of the current, then the thumb will indicate the direction of the force on a charge. The direction of current is always opposite to the direction of flow of electrons. With help of Fleming’s left hand rule, we can infer that the force is acting into the plane.