MHTCET 2016 Physics Solved Paper

(c) Total current through the galvanometer is given by
I=

V

Reff

=

2

1970+30

=

2

2000

= 10−3A
As this current provides full scale deflection (i.e. 20 div).
To get the deflection of 10 divisions, valueof resistance needed to connect can be obtained as
θ=

nIAB

K

(i.e.θ∝I)

θ1

θ2

=

I1

I2

=2
I2=

I1

2

=

10−3

2

= 5×10−4A
Now, I=

V

Reff+Rs

⇒ Rs=

V

I

−Reff =

2

5×10−4

−2000
=4×103−2000 = 2000 Ω
So, the resistance of 1970 Ω is to be replaced by 1970 + 2000 = 3970 Ω.