Electrical Magnetic Circuit Objective Test - ObjectiveBooks

# Practice Test: Question Set - 03

1. When both the inductance and resistance of a coil are doubled the value of
(A) Time constant remains unchanged
(B) Initial rate of rise of current is doubled
(C) Final steady current is doubled
(D) Time constant is halved

2. Hard steel is suitable for making permanent magnets because
(A) It has good residual magnetism
(B) Its hysteresis loop has large area
(C) Its mechanical strength is high
(D) Its mechanical strength is low

3. The relative permeability of a ferromagnetic material is
(A) Less than one
(B) More than one
(C) More than 10
(D) More than 100 or 1000

4. Relative permeability of vacuum is
(A) 1
(B) 1 H/m
(C) 1/4JI
(D) 4n × 10' H/m

5. Those materials are well suited for making permanent magnets which have ________ retentivity and ________ coercivity.
(A) Low, high
(B) High, high
(C) High, low
(D) Low, low

6. While comparing magnetic and electric circuits, the flux of magnetic circuit is compared with which parameter of electrical circuit?
(A) E.m.f.
(B) Current
(C) Current density
(D) Conductivity

7. Permeability in a magnetic circuit corresponds to______ in an electric circuit.
(A) Resistance
(B) Resistivity
(C) Conductivity
(D) Conductance

8. Energy stored by a coil is doubled when its current is increased by percent.
(A) 25
(B) 50.14
(C) 41.4
(D) 100

9. A material for good magnetic memory should have
(A) Low hysteresis loss
(B) High permeability
(C) Low retentivity
(D) High retentivity

10. Laminated cores, in electrical machines, are used to reduce
(A) Copper loss
(B) Eddy current loss
(C) Hysteresis loss
(D) All of the above

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