Question

A uniform magnetic field exists in the plane of paper pointing from left to right as shown in the figure given below. In the field, an electron and a proton move as shown. The direction of force experienced by the proton and the electron are:

• A. Forces both pointing into the plane of paper
• B. Forces both pointing out of the plane of paper
• C. Forces pointing into the plane of paper and out of the plane of paper for proton and electron respectively
• D. Forces pointing opposite and along the direction of the uniform magnetic field on proton and electron respectively

Answer 1

The correct option is A

Forces both pointing into the plane of paper

Applying the Fleming’s left hand rule, if we keep the index finger in the direction of the magnetic field, and the middle finger in the direction of current, which is same direction in which the proton is moving (since it is positively charged), and opposite to the direction in which the electron is moving (since it is negatively charged), the direction in which the force is experienced by them is given by the direction of thumb, which is pointing into the plane of the paper for both the cases.