1 ) The Base current in a transistor circuit changes from 45 µ A to 140 µ A . Accordingly , the collector current changes from 0.2 m A to 4 m A . The gain in current is ?

1 ) The Base current in a transistor circuit changes from  45 µ A  to  140 µ A .  Accordingly , the collector current changes from 0.2 m A  to  4 m A .  The gain in current is : -

A ) 36 A ,                                                   B ) 40 A ,

C ) 53 A ,                                                   D ) None of these ,

Correct Answer : -   B ) 40 A ,

Solution : -

Beta factor is also known as current gain factor .

∆ β  =  ∆ Ic  /  ∆ Iβ   . . . . . . . . . . . . eq. 1

∴    ∆ Ic  =  collector current  =  4 – 0.2 m A  =  3.8 x 10^(-3) A .

∴    ∆ Iβ  =  base current  =  140 – 45 µ A  =  95 x 10^(-6) A .

So put in eq. 1 : -

∆ β  =  3.8 x 10^(-3) A  /  95 x 10^(-6) A   ,

∆ β  =  0.04 x 10^(3) A  ,

∆ β  =  40 A , Answer .

 

2 ) A voltmeter has resistance of 2000 ohms and it can measure up to 2 V . If we want to increase its range to 10 V , then the required resistance in series will be : -

A ) 200 Ω  ,                                                          B ) 4500 Ω  ,

C ) 8000 Ω  ,                                              D ) None of these ,

Correct Answer : -   C ) 8000 Ω  ,

Solution : -

Initial resistance = G = 2000 ohm ,

Initial reading = 2 V ,

To increase the voltage , we have to put resistance in series .

So , required resistance in series will be : -

R  =  ( n – 1 ) G .

∴  n = 10 / 2  =  5 .

So , R  =  ( 5 – 1 ) 2000 ,

R  =  4 x 200  =  8000 Ω  ,  Answer .