Question

A resistance of 10 ohm is connected in left gab of meter bridge. two resistance 20 ohm and 20 ohm are connected in parallel in the right gab. find the position of null point

Answer 1

Answer:

Null point is found at l

1

=40 cm

Using balanced Wheatstone bridge condition,

X

2

=

100−l

1

l

1

∴

X

2

=

100−40

40

⟹ X=3Ω

Case 2 :

New null point is found at l

2

=50 cm

Using balanced Wheatstone bridge condition,

X

′

2

=

100−l

2

l

2

∴

X

′

2

=

100−50

50

⟹ X

′

=2Ω

Since the unknown resistance gets decreased, thus we have to connect a resistance R in parallel to X so that X

′

comes out to be 2Ω.

Thus resistance of parallel combination X

′

=

X+R

XR

∴ 2=

3+R

3R

⟹ R=6Ω

Hence 6Ω must be connected in parallel to unknown resistance X.