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IIT JEE Advanced 2007 Paper 1
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© examsnet.com
Question : 4
Total: 66
A resistance of 2 Ω is connected across one gap of a meter-bridge (the length of the wire is 100 cm) and an unknown resistance, greater than 2 Ω, is connected across the other gap. When these resistances are interchanged, the balance point shifts by 20 cm. Neglecting any corrections, the unknown resistance is
3 Ω
4 Ω
5 Ω
6 Ω
Validate
Solution:
Using Wheatstone bridge principle, we have the following for the two resistances mentioned here:
2
l
=
R
100
−
l
R
1
+
20
=
2
80
−
l
where R is the unknown resistance. Dividing the aboveequations, we get
l
+
20
100
−
l
=
80
−
l
l
l
2
20
= 8000 - 100 l - 80l +
l
2
⇒ 200l = 8000
⇒ l = 40 cm
Therefore, the unknown resistance is
R =
2
×
60
40
= 3 Ω
© examsnet.com
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