Electrical Engineering Materials

21. Due to which of the following fact, in India, aluminium is replacing copper?

1. Aluminium is more ductile and malleable than copper
2. Aluminium is available in plenty, cheaper and lighter than copper
3. Aluminium has lower resistivity than that of copper
4. Aluminium has less temperature co-efficient than copper

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22. Due to which of the following factors the brush wear rate is altered?

1. Speed of the machine
2. Contact pressure
3. Surface conditions of brush and commutator
4. Excessive sparking
5. All of the above

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23. Due to which of the following reasons aluminium does not corrode in atmosphere?

1. Aluminium is a noble metal
2. Atmospheric oxygen can only diffuse very slowly through the oxide layer which is formed on the surface of aluminium
3. No reaction with oxygen occurs ft
4. any of the above

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24. Due to which of the following reasons copper and aluminium are not used for heating elements?

1. Both have great tendency for oxidation
2. Both have low melting point
3. Very large length of wires will be required
4. All of the above

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25. Effect of moisture on the insulating materials is to

1. decrease dielectric constant
2. decrease dielectric strength
3. decrease insulation resistance
4. increase dielectric loss
5. all of the above

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26. For a hole which of the following statements is incorrect?

1. Holes can exist in certain semiconductors only
2. Holes can exist in any material including conductors
3. Holes may constitute an electric current
4. Holes can be considered as a net positive charge

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27. For a particular material the Hall coefficient was found to be zero. The material is

1. insulator
2. metal
3. intrinsic semiconductor
4. none of the above

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28. For germanium the forbidden energy gap is

1. 0.15 eV
2. 0.25 eV
3. 0.5eV
4. 0.7eV

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29. High resistivity materials are used in

1. precision instruments
2. heating elements
3. motor starters
4. incandescent lamps
5. all of the above

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30. If the resistance of a conductor does not vary in accordance with Ohm’s law it is known as

1. non-linear conductor
2. reverse conductor
3. bad-conductor
4. non-conductor

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