JEE Main 2026 Jan 21 Shift 1, Physics Q22: Wheatstone Bridge, Ammeter, Voltmeter And Potentiometer

The bridge satisfies $\frac{1}{2}=\frac{2}{4}$, so it is balanced — no current flows through the middle 1$\Omega$ resistor.

The network between A and B reduces to two parallel branches: $(1+2)=3\Omega$ in parallel with $(2+4)=6\Omega$, giving $R_{AB}=\frac{3\cdot 6}{3+6}=2\Omega$.

Total circuit resistance with the 1$\Omega$ internal resistance: $3\Omega$. Current $i=9/3=3$ A.

Heat dissipated between A and B in 60 s: $H=i^2{R}_{AB}t=9\times 2\times 60=1080$ J.