CIE iGCSE Co-Ordinated Science P4.5.4 Force on a current-carrying conductor Exam Style Questions Paper 1
▶️ Answer/Explanation
Reversing the magnetic field direction alone also reverses the direction of the force.
Since both the current and the field are reversed together, the two reversals cancel out, so the force acts in the same original direction.
✅ Answer: (A)
Question
The diagram shows a wire in a magnetic field. There is a current in the wire. This causes a force on the wire.
The current is now doubled and the direction of the magnetic field is reversed. What happens to the force?
▶️Answer/Explanation
Answer: C
Explanation: The force on a current-carrying wire in a magnetic field is given by \( F = BIL \), where \( B \) is the magnetic field, \( I \) is the current, and \( L \) is the length of the wire. Doubling the current doubles the force, and reversing the magnetic field reverses the direction of the force.
Question
The diagram shows a wire in a magnetic field. There is a current in the wire.
The force produced on the wire causes the wire to move into the page. The direction of the current is now reversed.
What happens to the wire?
A. It does not move at all.
B. It moves out of the page.
C. It moves sideways towards one of the poles of the magnet.
D. It still moves into the page.
▶️Answer/Explanation
Answer: B
Explanation: Reversing the direction of the current reverses the direction of the force acting on the wire. If the wire initially moved into the page, it will now move out of the page.
Question
The diagram shows a current-carrying wire in a magnetic field. The current and the magnetic field cause a downward force on the wire.
The poles of the magnet are now reversed so that the N-pole is on the right and the S-pole is on the left.
What happens to the force on the wire?
A) Its direction changes.
B) Its magnitude decreases.
C) Its magnitude increases.
D) It is unchanged.
▶️Answer/Explanation
Answer: A
Explanation: The direction of the force on a current-carrying wire in a magnetic field depends on the direction of the current and the direction of the magnetic field. Reversing the poles of the magnet will reverse the direction of the magnetic field, which in turn will reverse the direction of the force on the wire. Therefore, the correct answer is A.
Question
A wire is placed between two magnetic poles. There is a current in the wire in the direction shown. The wire experiences an upward force.
There is also a force on the wire in arrangements X, Y and Z.
In which of the arrangements is the force upwards?
A. X only
B. X and Y only
C. Z only
D. X, Y and Z
▶️Answer/Explanation
Answer: C