Magnetism & Electromagnetism Objective Type Questions - Set 04 - ObjectiveBooks

# Practice Test: Question Set - 04

1. When the current through the coil of an electromagnet reverses, the
(A) Direction of the magnetic field reverses
(B) Direction of the magnetic field remains unchanged
(C) Magnetic field expands
(D) Magnetic field collapses

2. A keeper is used to
(A) Change the direction of magnetic lines
(B) Amplify flux
(C) Restore lost flux
(D) Provide a closed path for flux

3. The unit for permeability is
(A) Wb/At × m
(B) At/m
(C) At/Wb
(D) Wb

4. What will be the magnetic potential difference across the air gap of 2 cm length in magnetic field of 200 AT/m?
(A) 2 AT
(B) 4 AT
(C) 6 AT
(D) 10 AT

5. When a solenoid is activated, the force that moves the plunger is
(A) An electromagnetic field
(B) A permanent magnetic field
(C) Varying voltage

6. How does the magnetic compass needle behave in a magnetic field?
(A) It assures a position right angle to magnetic field
(B) It starts rotating
(C) It assures a position which follows a line of magnetic flux
(D) None of the above

7. If a conductor is moved back and forth at a constant rate in a constant magnetic field, the voltage in the conductor will reverse polarity.
(A) True
(B) False

8. For which of the following materials the saturation value is the highest?
(A) Ferromagnetic materials
(B) Paramagnetic materials
(C) Diamagnetic materials
(D) Ferrites

9. There is 900 mA of current through a wire with 40 turns. What is the reluctance of the circuit if the flux is 400 Î¼Wb?
(A) 14,400 At/Wb
(B) 1,440 At/Wb
(C) 9,000 At/Wb
(D) 90,000 At/Wb

10. Magnetism of a magnet can be destroyed by
(A) Heating
(B) Hammering
(C) By inductive action of another magnet
(D) By all above methods

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