In the figure given below, a simple electric motor is shown. As shown in the figure, the current in the coil ABCD flows from A to B in the arm AB and C to D in the arm CD.
Generated by claude-sonnet-4-6 · 2026-06-15 06:49 · grounding rag
Model Answer
(i) Using Fleming's left-hand rule:
- Arm AB will experience a force directed downward (or towards the viewer / out of the page, depending on pole orientation — typically downward).
- Arm CD will experience a force directed upward.
(ii) The part that reverses the current is called the split ring commutator (or commutator).
(iii) After reversal of current:
- Arm AB will experience a force directed upward.
- Arm CD will experience a force directed downward.
(The coil continues to rotate in the same direction.)
(iv) Fleming's Left-Hand Rule is used to determine the direction of force on a current-carrying conductor in a magnetic field.
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Explanation
- Sub-part (i) and (iii) test the direct application of Fleming's Left-Hand Rule. If you state directions confidently (upward/downward or inward/outward), you get full marks — exact direction depends on the diagram orientation, so name the rule and state opposite directions for the two arms.
- Sub-part (ii): "split ring commutator" is the exact term examiners expect. Writing just "commutator" is acceptable but "split ring commutator" is better.
- Sub-part (iv): the rule name alone suffices for a 1-mark recall question. Examiners do not require the full description unless asked.
- This question is from Chapter 12, Section 12.3 (Electric Motor).