61. The following five statements are made with reference to the cascade amplifier:
    (1) It is CE followed by CB
    (2) It is CB followed by CE
    (3) The load on CE is the input resistance of CB
    (4) The Miller effect capacitance is increased compared to a CE stage
    (5) The load on the cascade should be less than that in CE
    Of the above five statements, the true statements are:

1. 1. only 1, 3

   
   
   

   2. only 2, 4

   
   
   

   3. only 1, 3, 5

   
   
   

   4. only 2, 4, 5

   
   
   

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   NA

   Correct Option: A

   NA

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62. The two stage of a cascade amplifier have individual upper cut off frequencies at f₁ = 5 MHz and f₂ = 3.33 MHz. The best approximation for the upper cut-off of the cascade is:

1. 1. 4.16 MHz

   
   
   

   2. 3.33 MHz

   
   
   

   3. 2.00 MHz

   
   
   

   4. 5.00 MHz

   
   
   

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   Upper cut-off frequency of first stage f₁ = 5 MHz
   upper cut-off frequency of II^nd stage f₂ = 3.33 MHz after cascading
   f₁* = f₁ √2^1/n= 1 = √2^1/2 - 1
   = √0·414 = 3.217 MHz
   

   after cascading f2* =	f2	=	3·33
   	√21/n - 1		√1·414 – 1

   
   = 5.17 MHz
   n = 2 (for two cascaded stage) upper cut-off after cascading the two stages
   = 5.17 – 3.217
   = 1.905 MHz ≈ 2 MHz

   Correct Option: C

   Upper cut-off frequency of first stage f₁ = 5 MHz
   upper cut-off frequency of II^nd stage f₂ = 3.33 MHz after cascading
   f₁* = f₁ √2^1/n= 1 = √2^1/2 - 1
   = √0·414 = 3.217 MHz
   

   after cascading f2* =	f2	=	3·33
   	√21/n - 1		√1·414 – 1

   
   = 5.17 MHz
   n = 2 (for two cascaded stage) upper cut-off after cascading the two stages
   = 5.17 – 3.217
   = 1.905 MHz ≈ 2 MHz

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63. In regard to class A single ended transformer coupled amplifier the following statements are made:
    1. The d.c. current flowing through primary causes considerable dissipation of power.
    2. The output a.c. power obtained is the same as in the series fed directly coupled load for a given transistor dissipation capability.
    3. In the presence of a signal, the transistor dissipation is less than in the case of direct coupled load.
    4. The drain on the power supply is ideally one-half of what it is in direct coupled amplifier.
    Of these four statements, the true ones are:

1. 1. 1 and 2

   
   
   

   2. 3 and 4

   
   
   

   3. 2 and 3

   
   
   

   4. 2 and 4

   
   
   

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   NA

   Correct Option: D

   NA

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64. Single stage transformer coupled class A amplifier is delivering the a.c. power to the load of 1.25 watts. The d.c. power from the d.c. supply is:

1. 1. 1.25 W

   
   
   

   2. 2.5 W

   
   
   

   3. 5 W

   
   
   

   4. 0.65 W

   
   
   

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   NA

   Correct Option: B

   NA

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65. Single stage transformer coupled class A power amplifier uses a transistor with maximum dissipation capability of 2.5 watts. The maximum a.c. power in the load is:

1. 1. 1.25 W

   
   
   

   2. 2.5 W

   
   
   

   3. 5.0 W

   
   
   

   4. 0.65 W

   
   
   

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   In class A transformer coupled
   

   η = 0·5 =	Po(ac)
   	Pi(dc)

   
   where,
   P_o(ac) → maximum ac power in the load
   P_i(dc) → maximum applied dc power to the amplifier
   given that P_{D (max)} = 2.5
   

   0.5 =	Po(ac)
   	PD(max) + Po(ac)

   
   

   0.5 =	Po(ac)
   	2.5 + Po(ac)

   
   1.25 + 0.5 P_{o (ac)} = P_{o (ac)}
   0.5 P_{o (ac)} = 1.25
   

   or Po (ac) =	1·25	= 2.5 watts.
   	·5

   Correct Option: B

   In class A transformer coupled
   

   η = 0·5 =	Po(ac)
   	Pi(dc)

   
   where,
   P_o(ac) → maximum ac power in the load
   P_i(dc) → maximum applied dc power to the amplifier
   given that P_{D (max)} = 2.5
   

   0.5 =	Po(ac)
   	PD(max) + Po(ac)

   
   

   0.5 =	Po(ac)
   	2.5 + Po(ac)

   
   1.25 + 0.5 P_{o (ac)} = P_{o (ac)}
   0.5 P_{o (ac)} = 1.25
   

   or Po (ac) =	1·25	= 2.5 watts.
   	·5

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