JEE Challenger
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Calculate Unknown Resistance in Meter Bridge with End Corrections

A meter bridge is set-up as shown, to determine an unknown resistance 'XX' using a standard 10 ohm10\text{ ohm} resistor. The galvanometer shows null point when tapping-key is at 52 cm52\text{ cm} mark. The end-corrections are 1 cm1\text{ cm} and 2 cm2\text{ cm} respectively for the ends AA and BB. The determined value of 'XX' is

Diagram 0

Options

A

10.2 ohm10.2\text{ ohm}

B

10.6 ohm10.6\text{ ohm}

Correct
C

10.8 ohm10.8\text{ ohm}

D

11.1 ohm11.1\text{ ohm}

Step-by-Step Solution

To determine the unknown resistance XX using a meter bridge, we use the principle of a balanced Wheatstone bridge.

At the null point, the ratio of the resistances in the two gaps is equal to the ratio of the resistances of the corresponding wire segments:
XR=RARB\frac{X}{R} = \frac{R_A}{R_B}

Since the resistance of a uniform wire is directly proportional to its effective length, we include the end corrections α\alpha and β\beta for ends AA and BB, respectively:
XR=l1+αl2+β\frac{X}{R} = \frac{l_1 + \alpha}{l_2 + \beta}

Given data:

  • Standard resistance, R=10 ΩR = 10\text{ }\Omega
  • Distance of the null point from end AA, l1=52 cml_1 = 52\text{ cm}
  • Remaining length of the wire towards end BB, l2=100−l1=100−52=48 cml_2 = 100 - l_1 = 100 - 52 = 48\text{ cm}
  • End-correction at end AA, α=1 cm\alpha = 1\text{ cm}
  • End-correction at end BB, β=2 cm\beta = 2\text{ cm}

Substitute these values into the bridge equation:
X10=52+148+2\frac{X}{10} = \frac{52 + 1}{48 + 2}

X10=5350\frac{X}{10} = \frac{53}{50}

Solving for XX:
X=10×5350=535=10.6 ΩX = 10 \times \frac{53}{50} = \frac{53}{5} = 10.6\text{ }\Omega

Thus, the determined value of XX is 10.6 ohm10.6\text{ ohm}.

Correct Option: B