Electrical Engineering Materials

31. In a crystal, an atom vibrates at a frequency determined by

1. the heat content of the crystal
2. the temperature of the crystal
3. the stiffness of the bonds it makes with neighbors
4. any of the above

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32. In a superconductor the value of critical density depends upon

1. magnetic field strength
2. temperature
3. either (a) or (b)
4. both (a) and (b)

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33. In conductors conduction of electricity takes place due to movement of

1. electrons only
2. positive ions only
3. negative ions only
4. positive and negative ions

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34. In graphite, bonding is

1. covalent
2. metallic
3. Vander Waals
4. Vander Waals and covalent

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35. In thermocouples which of the following pairs is commonly used?

1. Copper-constantan
2. Aluminium-tin
3. Silver-German silver
4. Iron-steel

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36. is a negatively charged particle present in an atom.

1. Proton
2. Neutron
3. Electron
4. None of the above

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37. is an element used in semiconductors whose atoms have three valence electrons.

1. An acceptor
2. A donor
3. Germanium
4. Silicon

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38. is the property of absorbing moisture from atmosphere.

1. Solubility
2. Viscosity
3. Porosity
4. Hygroscopicity

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39. Low resistivity materials are used in

1. transformer, motor and generator windings
2. transmission and distribution lines
3. house wiring
4. all above applications

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40. Mercury as an electric contact material is

1. a liquid
2. a metal
3. a metal liquid
4. a gas

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