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 :
pointing into the plane of the paper and out of the plane of the paper respectively.
pointing out of the plane of the paper and into the plane of the paper respectively.
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The Correct Option isA
Solution and Explanation
Step 1: Setup Description
- A uniform magnetic field is directed horizontally to the right within the plane of the paper.
- An electron (e⁻) and a positron (p⁺) both enter the field with their velocities oriented upwards, perpendicular to the magnetic field.
Step 2: Magnetic Force Calculation (Right-Hand Rule)
The magnetic force on a charged particle is quantified by the Lorentz force equation:
F = q (v × B)
- For a positive charge (positron): Orient fingers along velocity (upwards). Point the palm towards the magnetic field (to the right). The thumb indicates the force direction (into the paper).
- For a negative charge (electron): The force direction is opposite to that of a positive charge when applying the right-hand rule. Thus, the force on the electron also directs into the paper.
Step 3: Final Determination
Both the electron and the positron are subjected to forces directed into the plane of the paper.
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