Magnetism and Electromagnetism problems
- 1. What is the flux density in a magnetic field in which the flux in 0.1 m2 is 600 µWb?
Options- A. 6,000 µT
- B. 600 µT
- C. 600 T
- D. 6 T Discuss
Correct Answer: 6,000 µT
- 2. The induced voltage across a coil with 250 turns that is located in a magnetic field that is changing at a rate of 8 Wb/s is
Options- A. 1,000 V
- B. 2,000 V
- C. 31.25 V
- D. 3,125 V Discuss
Correct Answer: 2,000 V
- 3. The unit for reluctance is
Options- A. tesla
- B. At/Wb
- C. At/m
- D. Wb Discuss
Correct Answer: At/Wb
- 4. If a loop in a basic dc generator suddenly begins rotating at a faster speed, the induced voltage
Options- A. remains unchanged
- B. reverses polarity
- C. increases
- D. decreases Discuss
Correct Answer: increases
- 5. When the current through the coil of an electromagnet reverses, the
Options- A. direction of the magnetic field reverses
- B. direction of the magnetic field remains unchanged
- C. magnetic field expands
- D. magnetic field collapses Discuss
Correct Answer: direction of the magnetic field reverses
- 6. What is the reluctance of a material that has a length of 0.07 m, a cross-sectional area of 0.014 m2, and a permeability of 4,500 µWb/At × m?
Options- A. 1111 At/Wb
- B. 111 At/Wb
- C. 11 At/Wb
- D. 1 At/Wb Discuss
Correct Answer: 1111 At/Wb
- 7. When a solenoid is activated, the force that moves the plunger is
Options- A. an electromagnetic field
- B. a permanent magnetic field
- C. varying voltage
- D. a steady current Discuss
Correct Answer: an electromagnetic field
- 8. There is 900 mA of current through a wire with 40 turns. What is the reluctance of the circuit if the flux is 400 µWb?
Options- A. 14,400 At/Wb
- B. 1,440 At/Wb
- C. 9,000 At/Wb
- D. 90,000 At/Wb Discuss
Correct Answer: 90,000 At/Wb
- 9. The voltage induced across a certain coil is 200 mV. A 120 Ω resistor is connected to the coil terminals. The induced current is
Options- A. 1.7 mA
- B. 16 mA
- C. 12 mA
- D. 120 mA Discuss
Correct Answer: 1.7 mA
- 10. An electromagnetic field exists only when there is
Options- A. an increasing current
- B. decreasing current
- C. voltage
- D. current Discuss
Correct Answer: current
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