Quiz Chapter 4: Electromagnetism

1. According to Lenz's Law, the direction of an induced current is such that it always:

1. Aids the motion or change producing it
2. Opposes the motion or change producing it
3. Aligns parallel to the magnetic field lines
4. Flows from negative to positive potential externally

2. Which rule determines the direction of induced current in a straight conductor moving perpendicular to a magnetic field?

1. Fleming's Right-Hand Rule
2. Fleming's Left-Hand Rule
3. Right-Hand Grip Rule
4. Maxwell's Screw Rule

3. A copper rod falls vertically through a uniform horizontal magnetic field. What happens across the ends of the rod?

1. An electric potential difference is induced across its ends
2. The magnetic field vanishes instantly
3. The copper rod loses its gravitational mass
4. A steady direct current flows in a closed circle within the rod

4. When a straight wire carrying current towards the reader (out of the page) is placed in a magnetic field directed to the right, in which direction is the magnetic force on the wire?

1. Upward
2. Downward
3. To the left
4. To the right

5. Which change will NOT increase the speed of rotation of an electric motor?

1. Increasing the current supplied to the coil
2. Using stronger permanent magnets
3. Reversing the polarity of the power supply
4. Increasing the number of turns of the rectangular coil

6. Which factor causes energy loss due to hysteresis in a transformer?

1. Resistance of secondary winding copper wire
2. Repeated magnetisation and demagnetisation of the core material
3. Induced circulation currents within the solid core body
4. Leakage of magnetic flux into surrounding air

7. Why is electricity transmitted across long national distances at ultra-high voltages?

1. To increase current speed along transmission lines
2. To reduce current in cables, thereby minimizing I²R heating power loss
3. To lower the insulation requirements of transmission towers
4. To prevent lightning strikes on transmission towers

8. An ideal transformer steps down voltage from 240 V to 12 V. If the secondary current is 10 A, what is the current in the primary coil?

1. 0.5 A
2. 20 A
3. 2.0 A
4. 5.0 A

9. What is the primary function of a split-ring commutator in a direct current (d.c.) motor?

1. To increase the speed of rotation of the coil
2. To reverse the direction of current in the coil every half-revolution
3. To switch off the circuit automatically when overloaded
4. To reduce friction during high-speed rotation

10. Which rule is used to determine the direction of the magnetic force acting on a current-carrying conductor placed in a magnetic field?

1. Right-Hand Grip Rule
2. Fleming's Left-Hand Rule
3. Fleming's Right-Hand Rule
4. Lenz's Law