71. Under high electric fields, in a semiconductor increasing electric field—
    1. Mobility decreases
    2. Mobility increases
    3. Velocity saturates
    4. Velocity increases The correct statements are:

1. 1. 1 and 4 only

   
   
   

   2. 1 and 3 only

   
   
   

   3. All of the above

   
   
   

   4. None of these
      

   
   
   

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   Under high electric fields, in a semiconductor increasing electric field—
   ● Mobility decreases
   ● Velocity saturates

   Correct Option: B

   Under high electric fields, in a semiconductor increasing electric field—
   ● Mobility decreases
   ● Velocity saturates

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72. The ratio of diffusion constant to mobility of carriers—

1. 1. Depends on temperature

   
   
   

   2. Varies with lifetime

   
   
   

   3. Universal constant

   
   
   

   4. None of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   We know that		Dn	=	KT	= VT
   		µn		q

   
   The ratio of diffusion constant to mobility is depends on temperature.

   Correct Option: A

   We know that		Dn	=	KT	= VT
   		µn		q

   
   The ratio of diffusion constant to mobility is depends on temperature.

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73. A Clipper circuit always—

1. 1. Need a dc source

   
   
   

   2. Clips both cycles of input signal

   
   
   

   3. Clips upper portion of the signal

   
   
   

   4. Clips some part of the input signal

   
   
   

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1. View Hint View Answer Discuss in Forum

   A primary function of clamper circuit is to introduce a dc level into an ac level.

   Correct Option: D

   A primary function of clamper circuit is to introduce a dc level into an ac level.

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74. Pure Si is experimentally determined to exhibit a carrier (electron or hole) density of 1·48 × 10¹⁰ electrons (holes) cm³ at 300° K. If the electron mobility and hole mobility is 1300 cm²/Vs and 500 cm²/Vs, the resistivity of an intrinsic Si specimen at 300 °K is …………?

1. 1. 2·3⁵ × 10⁵ Ω m

   
   
   

   2. 1·18 × 10⁵ Ω m

   
   
   

   3. 2·35 × 10⁵ Ωcm

   
   
   

   4. Cannot be determined

   
   
   

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1. View Hint View Answer Discuss in Forum

   Given
   µ_i = 1·48 × 10¹⁰ cm³
   µ_n = 1300 cm²/V–s
   µ_p = 500 cm²/V–s
   i =?
   

   
   

   We know that, i =	1	=	1
   	i		q ni (µn + µp)

   
   

   or i =	1
   	1·6 × 10–19 × 1·48 × 1010 (1300 + 500)

   
   or i = 2·35 × 10⁵ Ω–cm
   Hence alternative (C) is the correct choice.

   Correct Option: C

   Given
   µ_i = 1·48 × 10¹⁰ cm³
   µ_n = 1300 cm²/V–s
   µ_p = 500 cm²/V–s
   i =?
   

   
   

   We know that, i =	1	=	1
   	i		q ni (µn + µp)

   
   

   or i =	1
   	1·6 × 10–19 × 1·48 × 1010 (1300 + 500)

   
   or i = 2·35 × 10⁵ Ω–cm
   Hence alternative (C) is the correct choice.

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75. Bridge rectifiers are preferred because—

1. 1. They require small transformer

   
   
   

   2. Less peak inverse voltage

   
   
   

   3. Both (A) and (B)

   
   
   

   4. None of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   Bridge rectifiers are preferred because
   * They require small transformer, and
   * Less peak inverse voltage

   Correct Option: C

   Bridge rectifiers are preferred because
   * They require small transformer, and
   * Less peak inverse voltage

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