Question

A uniform magnetic field exists in the plane of paper as shown in the diagram. In this field, an electron (e⁻) and a positron (p⁺) enter as shown. The electron and positron experience forces :

• A. both pointing into the plane of the paper.
• B. both pointing out of the plane of the paper.
• C. pointing into the plane of the paper and out of the plane of the paper respectively.
• D. pointing out of the plane of the paper and into the plane of the paper respectively.

Answer 1

The Correct Option is A

Step 1: Understand the setup
- A uniform magnetic field is acting to the right, in the plane of the paper.
- An electron (e⁻) and a positron (p⁺) are both entering the field with their velocity directed upward (perpendicular to the magnetic field).

Step 2: Apply the right-hand rule for magnetic force
The magnetic force on a charged particle is given by:
F = q (v × B)
- For a positive charge (positron), use the right-hand rule: Point fingers in the direction of velocity (up), palm in the direction of the field (right), then the thumb points in the direction of force (into the plane of paper).
- For a negative charge (electron), the direction of force is opposite to that for a positive charge using the same rule. So, for the electron, the force also points into the plane of paper.

Step 3: Conclusion
Both the electron and positron experience forces pointing into the plane of the paper.