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MHT CET 2021 Physics Solved Paper
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© examsnet.com
Question : 34
Total: 100
A potentiometer wire
A
B
having length
L
and resistance
12
r
is joined to a cell
D
of emf
ε
and internal resistance
r
. A cell
C
having emf
ε
2
and internal resistance
3
r
is connected. The length AJ at which galvanometer as shown in figure shows no deflection is
5
12
L
11
12
L
13
24
L
11
24
L
Validate
Solution:
(c) Given, length of wire,
A
B
=
L
Resistance of wire,
A
B
=
12
r
emf of cell
D
=
ε
, internal resistance of
D
=
r
emf of cell
C
=
ε
2
, internal resistance of
C
=
3
r
Current in potentiometer wire
(
i
)
=
Total emf
Total resistance
i
=
ε
r
+
12
r
=
ε
13
r
Potential drop across the balance length
A
J
of potentiometer wire is
V
A
J
=
i
×
R
A
J
⇒
V
A
J
=
i
(resistance per unit length
×
length
A
J
)
V
A
J
=
i
(
12
r
L
×
x
)
where,
x
is the balance length
A
J
.
As null point occurs at
J
, so potential drop across balance length,
A
J
=
emf of cell
C
V
A
J
=
ε
2
⇒
i
(
12
r
L
×
x
)
=
ε
2
⇒
ε
13
r
×
12
r
L
×
x
=
ε
2
⇒
x
=
13
24
L
© examsnet.com
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