251. The conduction band in a semiconductor is:

1. 1. due to the spreading of energies of free electrons

   
   
   

   2. another name for forbidden energy gap

   
   
   

   3. at the top of a crystal

   
   
   

   4. None of the above

   
   
   

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   The conduction band in a semiconductor is due to the spreading of energies of free electrons.

   Correct Option: A

   The conduction band in a semiconductor is due to the spreading of energies of free electrons.

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252. Tunnel diodes are fabricated from:

1. 1. GaAs

   
   
   

   2. Si

   
   
   

   3. Ge

   
   
   

   4. C

   
   
   

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1. View Hint View Answer Discuss in Forum

   Tunnel diodes are fabricated from GaAs.

   Correct Option: A

   Tunnel diodes are fabricated from GaAs.

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253. Which of the following pairs are correctly matched?
     

     1. Nordheim equation:	Effect of alloying on resistivity
     2. Lorentz number:	µh ∝ T2·4
     3. Wiedemana-Franz law:	ne >> nh
     4. Matthilssen rule:	Total resistivity in the sum of different effects

     
     Select the correct answer using the codes given below:

1. 1. 2 and 3

   
   
   

   2. 1 and 4

   
   
   

   3. 1 and 2

   
   
   

   4. 1, 2 and 4

   
   
   

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   NA

   Correct Option: B

   NA

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254. An example of a metal having zero Thomson effect is:

1. 1. zinc

   
   
   

   2. cobalt

   
   
   

   3. lead

   
   
   

   4. rhodium

   
   
   

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   NA

   Correct Option: C

   NA

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255. Highest electrical resistivity exists in:

1. 1. platinum wire

   
   
   

   2. nichrome wire

   
   
   

   3. silver wire

   
   
   

   4. kanthal wire

   
   
   

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   Highest electrical resistivity exists in kanthal wire.

   Correct Option: D

   Highest electrical resistivity exists in kanthal wire.

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