The Motor Effect Quiz

1. A current-carrying conductor is placed perpendicular to a magnetic field. Which of the following correctly describes the motor effect?

• A. A force acts on the conductor perpendicular to both the current direction and the magnetic field direction
• B. A force acts on the conductor in the same direction as the current
• C. A force acts on the conductor parallel to the magnetic field lines
• D. No force acts on the conductor because current and magnetic fields cannot interact

2. Using Fleming's left-hand rule, if your thumb points in the direction of the current and your first finger points in the direction of the magnetic field, what does your middle finger represent?

• A. The direction of the magnetic flux density
• B. The direction of the force on the conductor
• C. The direction of electron flow
• D. The magnitude of the current

3. A current-carrying wire of length 0.5 m is placed perpendicular to a magnetic field of strength 2 T. If the current is 4 A, calculate the force on the wire.

• A. 0.25 N
• B. 2 N
• C. 4 N
• D. 16 N

4. In a simple d.c. motor, the coil rotates continuously because the commutator repeatedly reverses the direction of the current. What is the purpose of this reversal?

• A. To increase the strength of the magnetic field
• B. To ensure the force on the coil always acts in the same rotational direction
• C. To reduce energy loss as heat
• D. To change the kinetic energy into electrical energy

5. A student wants to increase the turning effect (moment) of a d.c. motor. Which combination of changes would most effectively achieve this?

• A. Decrease the current and increase the magnetic flux density
• B. Increase the number of coils, increase the current, and increase the area of each coil
• C. Increase the temperature of the coil and decrease the length of the conductors
• D. Reverse the direction of the current and reduce the number of poles in the magnet