The circuit shown here is used to compare the $e.m.f.$ of two cells ${E_1}$ and ${E_2}({E_1} > {E_2})$. The null point is at $C$ when the galvanometer is connected to ${E_1}$. When the galvanometer is connected to ${E_2}$, the null point will be
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(a) $E \propto l$ (balancing length)
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In the box shown current $i$ enters at $H$ and leaves at $C$. If $i_{AB} = \frac{{\text{i}}}{6}$ , $i_{DC} = \frac{{\text{2i}}}{3}$ ,$i_{HA} = \frac{{\text{i}}}{2} , i_{GF} = \frac{{\text{i}}}{6} , i_{HE} = \frac{{\text{i}}}{6}$ , choose the branch in which current is zero
First, a set of ${n}$ equal resistors of $10\; \Omega$ each are connected in series to a battery of emf $20\; {V}$ and internal resistance $10\; \Omega .$ A current $I$ is observed to flow. Then, the $n$ resistors are connected in parallel to the same battery. It is observed that the current is increased $20$ times, then the value of $n$ is .... .
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To measure the temperature coefficient of resistivity $\alpha$ of a semiconductor, an electrical arrangement shown in the figure is prepared. The arm BC is made up of the semiconductor. The experiment is being conducted at $25^{\circ} \mathrm{C}$ and resistance of the semiconductor arm is $3 \mathrm{~m} \Omega$. Arm BC is cooled at a constant rate of $2^{\circ} \mathrm{C} / \mathrm{s}$. If the galvanometer $\mathrm{G}$ shows no deflection after $10 \mathrm{~s}$, then $\alpha$ is :