CIE iGCSE Co-Ordinated Science P4.5.5 The d.c. motor Exam Style Questions Paper 1
▶️ Answer/Explanation
Reversing the current direction only reverses the direction of rotation of the coil.
The magnitude of the turning effect itself stays the same when only the current direction is reversed.
✅ Answer: (A)
Question
Which pair of changes must make the coil of an electric motor rotate more quickly?
| number of turns on the coil | current in the coil | |
|---|---|---|
| A | decreases | decreases |
| B | decreases | increases |
| C | increases | decreases |
| D | increases | increases |
▶️Answer/Explanation
Answer: D. increases, increases
Explanation: Increasing the number of turns on the coil and increasing the current in the coil both increase the magnetic force acting on the coil, causing it to rotate more quickly.
Question
There is a current in a coil of wire. The coil rotates between the poles of a magnet. Which change does not increase the turning effect on the coil?
A) increasing the current in the coil
B) reversing the current
C) using a stronger magnet
D) using more turns in the coil
▶️Answer/Explanation
Answer: B) reversing the current
Explanation: Reversing the current changes the direction of the turning effect but does not increase its magnitude. Increasing the current, using a stronger magnet, or using more turns in the coil all increase the turning effect.