iGCSE Physics (0625) 4.5.5 d.c. motor-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
The turning effect (torque) on a coil in a magnetic field is directly proportional to the current I and the number of turns N.
Mathematically, the turning effect can be expressed by the relationship τ∝B⋅I⋅A⋅N, where B is the magnetic field strength and A is the area.
To ensure an increase in the turning effect, both variables I and N should be changed in a way that maximizes their product.
Increasing the current I provides more force per unit length of the wire according to F=BIl.
Increasing the number of turns N adds more lengths of wire, thereby multiplying the total force acting on the sides of the coil.
Therefore, only option D, which suggests increasing both the current and the number of turns, guaranteed an increase in the turning effect.
Question
A class is designing a d.c. motor. To achieve a greater turning effect, three suggestions are made.
Have a larger current in the coil of the motor.
Have a stronger magnet in the motor.
Put a larger number of turns on the coil.
Which suggestions will help to increase the turning effect?
A 1, 2 and 3
B 1 and 2 only
C 1 and 3 only
D 2 and 3 only
Answer/Explanation
Ans: A
Question
The diagram shows a simple d.c. electric motor which is rotating.
Which change makes the motor rotate more quickly?
increasing the number of turns on the coil
removing the magnets
reversing the battery
reversing the polarity of the magnets
Answer/Explanation
Ans: A