Magnetic Circuit

21. The relative permeability of a ferromagnetic material is

1. less than one
2. more than one
3. more than 10
4. more than 100 or 1000

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22. The unit of magnetic flux is

1. henry
2. weber
3. ampereturn/weber
4. ampere/metre

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23. The unit of reluctance is

1. metre/henry
2. henry/metre
3. henry
4. 1/henry

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24. The unit of retentivity is

1. weber
2. weber/sq. m
3. ampere turn/meter
4. ampere turn

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25. Those magnetic materials are best suited for making armature and transformer cores which have _________ permeability and _________ hystersis loss.

1. high, high
2. low, high
3. high, low
4. low, low

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26. Those materials are well suited for making permanent magnets which have _________ retentivity and _________ coercivity.

1. low, high
2. high, high
3. high, low
4. low, low

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27. When both the inductance and resistance of a coil are doubled the value of

1. time constant remains unchanged
2. initial rate of rise of current is doubled
3. final steady current is doubled
4. time constant is halved

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28. While comparing magnetic and electric circuits, the flux of magnetic circuit is compared with which parameter of electrical circuit ?

1. E.m.f.
2. Current
3. Current density
4. Conductivity

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