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  • (i) State the principle of working of a meter bridge. Draw the circuit diagram for finding an unknown resistance using a meter bridge. Derive the relevant formula used. (ii) In a meter bridge with R and S in the gaps, the null point is found

(i) State the principle of working of a meter bridge. Draw the circuit diagram for finding an unknown resistance using a meter bridge. Derive the relevant formula used.

(ii) In a meter bridge with R and S in the gaps, the null point is found at 40 cm from A. If a resistance of 30\Omega  is connected in parallel with S, the null point occurs at 50 cm from A. Determine the values of R and S.

 

 

 

 
 
 
 
 

Answers (1)

i) Meter bridge works on the principle of Wheatstone bridge

Wheatstone bridge

The connections are made as in the circuit. During balance condition, no current flows through the galvanometer

\therefore \frac{P}{Q}=\frac{R}{S}

Meter bridge

The length of the wire AB is 1m = 100 cm.

S is the unknown resistance

R is the resistance chosen from the resistance both Galvanometer G is connected to a Jockey. The Jockey is moved on the wire  AB to obtain the null point. Let the null point be obtained at P, then

the resistance of AP\alpha L and resistance of PB\alpha (100-l)

from the Wheatstone bridge principle

\frac{R}{S}=\frac{l}{100-l}

known resistance

S=\frac{R(100-l)}{l}

(ii) Case 1

\frac{R}{S}=\frac{40}{60}=\frac{2}{3}---(1)

Case 2

\frac{R(30+S)}{30S}=1 ----(2)

From (1) and (2)

\Rightarrow \frac{30}{30+S}=\frac{2}{3}

\Rightarrow 60+25=90

\Rightarrow S=15\Omega

From (1)

\frac{R}{15}=\frac{2}{3}

R=10\Omega

Posted by

Safeer PP

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