| 1. | The relative permeability of a ferromagnetic material is ? | |
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less than one
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more than one
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more than 10
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more than 100 or 1000
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Report Question| 2. | In a magnetic material hysteresis loss takes place primarily due to ? | |
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rapid reversals of its magnetisation
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flux density lagging behind magnetising force
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molecular friction
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it high retentivity
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| 3. | Hard steel is suitable for making permanent magnets because ? | |
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it has good residual magnetism
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its hysteresis loop has large area
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its mechanical strength is high
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its mechanical strength is low
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| 4. | Point out the wrong statement. Magnetic leakage is undesirable in electric machines because it ? | |
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lowers their power efficiency
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increases their cost of manufacture
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leads to their increased weight
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produces fringing
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| 5. | Those materials are well suited for making permanent magnets which have retentivity and coercivity ? | |
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low, high
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high, high
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high, low
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low, low
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| 6. | The rate of rise of current through an inductive coil is maximum ? | |
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at 63.2% of its maximum steady value
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at the start of the current flow
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after one time constant
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near the final maximum value of current
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| 7. | Energy stored by a coil is doubled when its current is increased by percent ? | |
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25
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41.4
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50
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100
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| 8. | An air gap is usually inserted in magnetic circuits to ? | |
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increase m.m.f.
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increase the flux
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prevent saturation
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none of the above
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| 9. | A ferrite core has less eddy current loss than an iron core because ? | |
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ferrites have high resistance
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ferrites are magnetic
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ferrites have low permeability
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ferrites have high hysteresis
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| 10. | The magnetising force (H) and magnetic flux density (B) are connected by the relation ? | |
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B = ?rH/?o
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B = ?H
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B = H/ ?o?r
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B = ?oH/?r
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