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Concepts Of Physics MCQ Edition [Volume 2]PhysicsElectric Current through Gases

When the load resistance of an amplifier is modified from 4 k to 8 k , its gain factor increases from 10 to 12 . Determine the amplification factor.

Options

  1. A20
  2. B15
  3. C10
  4. D12

Correct answer

B. 15

Step-by-step solution

The voltage gain A_v of an amplifier is given by the relation: A_v = R_L r_p + R_L where is the amplification factor, R_L is the load resistance, and r_p is the internal resistance. For the first case, R_L = 4 k and A_v = 10 : 10 = 4 r_p + 4 10r_p + 40 = 4 5r_p + 20 = 2 For the second case, R_L = 8 k and A_v = 12 : 12 = 8 r_p + 8 12r_p + 96 = 8 3r_p + 24 = 2 Equating the expressions for 2 : 5r_p + 20 = 3r_p + 24 2r_p = 4 r_p = 2 k Substituting the value of r_p into the equation for 2 : 2 = 5(2) + 20 = 30 = 15

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