Question

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

• 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 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 in the direction in which the proton is moving (since it is positively charged), and in the opposite direction to which the electron is moving (since it is negatively charged), the direction in which the force is experienced by them will be in the direction of the thumb, which is pointing into the plane of the paper.