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 .
