In the circuit shown, a four wire potentiometer is made of a $400\, cm$ long wire, which extends between $A$ and $B$. The resistance per unit length of the potentiometer wire is $r = 0.01\, \Omega /cm$. If an ideal voltmeter is connected as shown with jockey $J$ at $50\, cm$ from end $A$, the expected reading of the voltmeter will be: ............... $V$
JEE MAIN 2019, Medium
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Resistance of wire $A B=400 \times 0.01=4 \,\Omega$ $\mathrm{i}=\frac{3}{6}=0.5\, \mathrm{A}$
Now voltmeter reading $=$ $i$ (Resistance of $50 \,\mathrm{cm}$ length)
$=(0.5 \mathrm{A})(0.01 \times 50)=0.25$ $volt$
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