- 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
Magnetic Circuit
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When both the inductance and resistance of a coil are doubled the value of_____.
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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
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The relative permeability of a ferromagnetic material is_____.
- A. Less than one
- B. More than one
- C. More than 10
- D. More than 100 Ωr 1000
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Those magnetic materials are best suited for making armature and transformer cores which have ____permeability and ____hysteresis loss.
- A. High, high
- B. Low, high
- C. High, low
- D. Low, low
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The rate of rise of current through an inductive coil is maximum_____.
- A. At 63.2% of its maximum steady value
- B. At the start of the current flow
- C. After one time constant
- D. Near the final maximum value of current
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A ferrite core has less eddy current loss than an iron core because_____.
- A. Ferrites have high resistance
- B. Ferrites are magnetic
- C. Ferrites have low permeability
- D. Ferrites have high hysteresis
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Silicon steel is used in electrical machines because it has_____.
- A. Low coercivity
- B. Low retentivity
- C. Low hysteresis loss
- D. High coercivity
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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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Energy stored by a coil is doubled when its current is increased by percent.
- A. 25
- B. 50.14
- C. 41.4
- D. 100
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The property of a material which opposes the creation of magnetic flux in it is known as_____.
- A. Reluctivity
- B. Magneto-motive force
- C. Permeance
- D. Reluctance