Read the following and answer the questions below.
Oersted's accidental discovery in 1820 revealed that a compass needle placed near a current-carrying wire gets deflected. This showed that a moving electric charge creates a magnetic field in the surrounding space. It was later established that a current-carrying conductor, when placed in an external magnetic field, experiences a mechanical force. This discovery led to the development of several devices that convert electrical energy into mechanical energy.
(a) What conclusion did Oersted draw from the deflection of the compass needle placed near the current-carrying wire? [1]
(b) In what direction does a compass needle placed below a horizontal wire (with current flowing from south to north) deflect — towards the east or towards the west? [1]
(c) State the rule that gives the direction of the force on a current-carrying conductor placed perpendicular to a magnetic field. [1]
(d) Name one device that converts electrical energy into mechanical energy using the force on a current-carrying conductor in a magnetic field. [1]
Generated by claude-sonnet-4-6 · 2026-06-26 01:11 · grounding rag
Model Answer
(a) Oersted concluded that a current-carrying wire produces a magnetic field around it, showing that electricity and magnetism are linked phenomena.
(b) When current flows from south to north and the compass is placed below the wire, the needle deflects towards the west (opposite to when the compass is above the wire with the same current direction).
(c) Fleming's Left-Hand Rule: Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, then the thumb points in the direction of force on the conductor.
(d) Electric motor — it converts electrical energy into mechanical energy using the force on a current-carrying conductor in a magnetic field.
Source: Chapter 12, Sections 12.1, 12.2, 12.3
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Explanation
- (a) The key conclusion is the link between electricity and magnetism — examiners expect this exact phrase.
- (b) Activity 12.4 states: current south→north, compass above → deflects west. When the compass is placed below, by symmetry the field direction reverses relative to the needle, so it deflects west in the scenario given. Stick to what the textbook Activity describes.
- (c) Fleming's Left-Hand Rule must name all three fingers and what each represents. Missing any part loses marks.
- (d) Electric motor is the most direct answer from the textbook. Loudspeaker is also acceptable but electric motor is preferred.