Question 1 · MCQ · Analyse · 1 mark
Reversing a straight-wire current
Magnetic field lines
A compass near a straight current-carrying wire deflects. The current is reversed while the setup remains fixed. What happens to the wire’s magnetic field direction?
(A) It stays the same everywhere.
(B) It reverses.
(C) It becomes gravitational.
(D) It must disappear permanently.
Show answer and solution
Answer: (B) It reverses.
Worked solution: The right-hand thumb rule relates field direction to current direction. Reversing the current reverses the circular magnetic field.
Question 2 · MCQ · Analyse · 1 mark
Strengthening an electromagnet
Fields of coils and solenoids
For the same solenoid and safe operating conditions, which change generally strengthens its magnetic field?
(A) Reducing current to zero
(B) Removing all its turns
(C) Increasing the current
(D) Replacing the wire with an open circuit
Show answer and solution
Answer: (C) Increasing the current
Worked solution: A solenoid’s magnetic field increases with current when its geometry and other conditions are kept fixed. An open circuit cannot sustain the current.
Question 3 · MCQ · Analyse · 1 mark
Reversing one direction
Force on a current-carrying conductor
A wire carrying current perpendicular to a magnetic field experiences a force. If only the current is reversed, what happens to the force direction?
(A) It reverses.
(B) It remains unchanged.
(C) It becomes parallel to both current and field.
(D) It must double in magnitude.
Show answer and solution
Answer: (A) It reverses.
Worked solution: Fleming’s left-hand rule gives the force direction. Reversing one of current or field reverses the force; the magnitude need not double.
Question 4 · MCQ · Analyse · 1 mark
Placing a fuse correctly
Domestic electric circuits
Where should a suitable fuse be connected in a domestic appliance circuit?
(A) In parallel with the appliance
(B) Only in the earth wire
(C) Between two points on the same neutral conductor
(D) In series in the live wire
Show answer and solution
Answer: (D) In series in the live wire
Worked solution: A fuse must carry the appliance current and disconnect the live supply when excessive current melts it. A parallel fuse would not perform that role.
Question 5 · A-R · Analyse · 1 mark
Why field lines do not cross
Magnetic field lines
Assertion (A): Magnetic field lines do not intersect at a point.
Reason (R): A compass needle at a point has one definite direction of alignment with a non-zero magnetic field.
(a) Both A and R are true, and R correctly explains A.
(b) Both A and R are true, but R does not correctly explain A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show answer and solution
Answer: (A) Both A and R are true, and R correctly explains A.
Worked solution: Intersecting field lines would imply two directions for the same resultant magnetic field at one point.
Question 6 · A-R · Analyse · 1 mark
Interpreting a mains frequency
Alternating and direct current
Assertion (A): A 50 Hz alternating current changes direction only 50 times per second.
Reason (R): One complete AC cycle contains two reversals of current direction.
(a) Both A and R are true, and R correctly explains A.
(b) Both A and R are true, but R does not correctly explain A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show answer and solution
Answer: (D) A is false, but R is true.
Worked solution: 50 Hz means 50 cycles per second. Since each cycle has two direction reversals, there are 100 reversals per second.
Question 7 · VSA · Apply · 2 marks
A pole changes on reversal
Fields of coils and solenoids
A solenoid’s left end behaves as a north pole. What happens to that end when the current direction is reversed, with all other conditions unchanged?
Show answer and solution
Answer: It becomes a south pole.
Worked solution: Reversing the current reverses the solenoid’s magnetic field, interchanging its north and south poles.
Question 8 · VSA · Apply · 2 marks
Why orientation matters
Force on a current-carrying conductor
A straight current-carrying wire is placed parallel to a uniform magnetic field. Compare its magnetic force with that when the wire is perpendicular to the field at the same current.
Show answer and solution
Answer: Parallel: zero magnetic force in the ideal model; perpendicular: maximum force for the same field, current and wire length.
Worked solution: The magnetic force depends on the angle between current and field. It vanishes for parallel directions and is greatest for perpendicular directions.
Question 9 · SA · Analyse · 3 marks
Why an earth wire matters
Domestic electric circuits
A fault connects the live wire to the metal body of an appliance. Explain the protective role of a properly connected earth wire and suitable fuse or circuit breaker.
Show answer and solution
Answer: The earth wire offers a low-resistance fault path, helping protective devices disconnect the supply.
Worked solution: Without protection, the metal case can become live. An earth connection provides a low-resistance path for fault current and helps keep the case near earth potential. A suitably rated fuse or circuit breaker can then interrupt the excessive current. Earthing does not replace proper insulation.
Question 10 · SA · Analyse · 3 marks
Testing the right-hand rule
Magnetic field lines
A straight wire carries current vertically upward. Viewed from above, what is the direction of its circular magnetic field? Predict the result if current is downward and explain the rule used.
Show answer and solution
Answer: Upward current: anticlockwise as viewed from above; downward: clockwise.
Worked solution: Point the right thumb in the direction of conventional current. The curled fingers show the field direction. Upward current points towards the observer looking down from above, giving anticlockwise circles; reversal gives clockwise circles.
Question 11 · LA · Analyse · 5 marks
Evaluating a safe household connection
Domestic electric circuits
Explain (i) why household appliances are connected in parallel, (ii) why the switch belongs in the live wire, (iii) how overloading differs from a short circuit, (iv) how a fuse responds, and (v) why a fuse alone does not replace earthing for a metal-bodied appliance.
Show answer and solution
Answer: Parallel gives each appliance the supply voltage; live switching isolates it; overloading and short circuits can both cause excessive current; a fuse melts; earthing provides a protective fault path.
Worked solution: Parallel branches allow independent operation at the rated supply voltage. Opening the live wire disconnects the appliance from the live supply. Overloading occurs when total current exceeds a circuit’s safe capacity; a short circuit is an unintended very low-resistance path, often between live and neutral. Excess current heats and melts a correctly rated fuse. Earthing helps conduct fault current safely and activate protection if the case becomes live.
Question 12 · Case Study · Analyse · 4 marks
Three conductor trials
Force on a current-carrying conductor
A short straight wire is held perpendicular to a uniform magnetic field. In trial P, it carries current and moves left. In trial Q, only the current is reversed. In trial R, both current and magnetic field are reversed relative to P.
Answer the following:
(i) Predict the force direction in Q. [1 mark]
(ii) Predict the force direction in R. [1 mark]
(iii) Name the rule used and explain why reversing both directions restores the original force direction. [2 marks]
Show answer and solution
Answer: (i) Right. (ii) Left. (iii) Fleming’s left-hand rule; each single reversal reverses force, so two reversals restore it.
Worked solution: The field, conventional current and force directions are mutually perpendicular. Reversing only one changes the force direction. Reversing both gives two direction changes and therefore the same force direction as in P.
