During an experiment with a metre bridge, the galvanometer shows a null point when the jockey is pressed at 40.0 cm using a standard resistance of $90 Ω$ , as shown in the figure. The least count of the scale used in the metre bridge is $1 mm$ . The unknown resistance is [2014]

Question

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(3)

In case of balanced meter bridge

$\frac{R}{l} = \frac{X}{100 - l}$

$Given: X = 90 Ω, l = 40.0 cm$

$∴$ $R = \frac{X l}{100 - l} = \frac{90 \times 40}{60} = 60 Ω$

$∴$ $\frac{Δ R}{R} = \frac{Δ l}{l} + \frac{Δ (100 - l)}{100 - l}$ $\Rightarrow \frac{Δ R}{60} = \frac{0.1}{40} + \frac{0.1}{60}$

$∴$ $Δ R = 0.25 Ω$

$∴$ $R = (60 \pm 0.25) Ω$

Solution

Q.
During an experiment with a metre bridge, the galvanometer shows a null point when the jockey is pressed at 40.0 cm using a standard resistance of $90 Ω$ , as shown in the figure. The least count of the scale used in the metre bridge is $1 mm$ . The unknown resistance is [2014]

1 $60 \pm 0.15 Ω$

2 $135 \pm 0.56 Ω$

3 $60 \pm 0.25 Ω$

4 $135 \pm 0.23 Ω$

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Solution

Q. During an experiment with a metre bridge, the galvanometer shows a null point when the jockey is pressed at 40.0 cm using a standard resistance of 90 Ω, as shown in the figure. The least count of the scale used in the metre bridge is 1 mm. The unknown resistance is [2014]

1 60±0.15Ω

2 135±0.56Ω

3 60±0.25Ω

4 135±0.23Ω