An alpha particle (positively charged) moves horizontally towards the east and enters a magnetic field directed vertically downward. Using Fleming's left-hand rule, determine the direction of force acting on the alpha particle.
Generated by claude-sonnet-4-6 · 2026-06-26 01:12 · grounding rag
Model Answer
Applying Fleming's Left-Hand Rule:
- Stretch the left hand so that the forefinger, middle finger, and thumb are mutually perpendicular.
- Forefinger → direction of magnetic field: vertically downward
- Middle finger → direction of current (conventional, same as motion of positive charge): towards east
- Thumb → direction of force on the alpha particle: towards north
Therefore, the force acting on the alpha particle is directed towards the north.
(The alpha particle, being positively charged, has its conventional current direction same as its velocity, i.e., eastward.)
Source: Chapter 12, Section — A current-carrying conductor in a magnetic field experiences a force given by Fleming's left-hand rule.
---
Explanation
- Key point: An alpha particle is positively charged, so conventional current direction = direction of its motion (east).
- In Fleming's Left-Hand Rule: Forefinger = Field, Middle finger = current (Motion for positive charge), Thumb = Thrust (force).
- Setting forefinger downward (field) and middle finger eastward (current), the thumb points north — that is the answer examiners expect.
- Do not confuse with Fleming's Right-Hand Rule (used for induced current/generators).