Heating and Welding

21. By which of the following methods the temperature inside arc nace can be varied?

1. By disconnecting some of the heating elements
2. By varying the operating voltage
3. By varying the current through heating elements
4. By any of the above method

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22. In induction heating __________ is abnormally high.

1. phase angle
2. frequency
3. current
4. voltage

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23. By the use of which of the following, high frequency power supply for induction furnaces can be obtained?

1. Coreless transformers
2. Current transformers
3. Motor-generator set
4. Multi-phase transformer

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24. Induction furnaces are employed for which of the following?

1. Heat treatment of castings
2. Heating of insulators
3. Melting aluminium
4. None of the above

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25. In an electric room heat convector the method of heating used is

1. arc heating
2. resistance heating
3. induction heating
4. dielectric heating

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26. In a domestic cake baking oven the temperature is controlled by

1. voltage variation
2. thermostat
3. auto-transformer
4. series-parallel operation

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27. In an electric press mica is used

1. as an insulator
2. as a device for power factor improvement
3. for dielectric heating
4. for induction heating

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28. Induction heating takes place iitwhich of the following?

1. Insulating materials
2. Conducting materials which are magnetic
3. Conducting materials which are non-magnetic
4. Conducting materials which may or may not be magnetic

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29. For heating element high resistivity material is chosen to

1. reduce the length of heating element
2. increase the life of the heating element
3. reduce the effect of oxidation
4. produce large amount of heat

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30. In resistance heating highest working temperature is obtained from heating elements made of

1. nickel copper
2. nichrome
3. silicon carbide
4. silver

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