Question:
In metre bridge experiment, the resistance in the left gap is 15 \(\Omega\) and in the right gap is 45 \(\Omega\). The bridge is balanced. The distance of the null point from the centre of the wire is
In metre bridge experiment, the resistance in the left gap is 15 \(\Omega\) and in the right gap is 45 \(\Omega\). The bridge is balanced. The distance of the null point from the centre of the wire is
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Balance condition: R_left / R_right = l / (100 - l); then subtract 50 cm.
Updated On: Oct 1, 2026
- \(80\) cm
- \(60\) cm
- \(40\) cm
- \(25\) cm
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept
In a metre bridge, at balance \(\dfrac{R}{S} = \dfrac{l}{100 - l}\), where \(l\) is the length from the left end (in cm).
Step 2: Compute
\[ \frac{15}{45} = \frac{l}{100 - l} \Rightarrow 100 - l = 3l \Rightarrow l = 25 \text{ cm} \]
The centre of the wire is at 50 cm, so the null point is \(50 - 25 = 25\) cm from the centre. Option (C), 40 cm, and (A), 80 cm, are not the result of this balance.
Final Answer:
The null point is 25 cm from the centre, option (D). \[ \boxed{25 \text{ cm}} \]
In a metre bridge, at balance \(\dfrac{R}{S} = \dfrac{l}{100 - l}\), where \(l\) is the length from the left end (in cm).
Step 2: Compute
\[ \frac{15}{45} = \frac{l}{100 - l} \Rightarrow 100 - l = 3l \Rightarrow l = 25 \text{ cm} \]
The centre of the wire is at 50 cm, so the null point is \(50 - 25 = 25\) cm from the centre. Option (C), 40 cm, and (A), 80 cm, are not the result of this balance.
Final Answer:
The null point is 25 cm from the centre, option (D). \[ \boxed{25 \text{ cm}} \]
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