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The length of a potentiometer wire is $l$. $A$ cell of $\mathrm{emf}$ $E$ is balanced at a length $l/3$ from the positive end of the wire. If the length of the wire is increased by $l/2$. At what distance will the same cell give a balance point.
For what value of unknown resistance $X$, the potential difference between $B$ and $D$ will be zero in the circuit shown in the figure ............... $\Omega$
Consider a block of conducting material ofresistivity '$\rho$' shown in the figure. Current '$I$' enters at '$A$' and leaves from '$D$'. We apply superp osition principle to find voltage '$\Delta V$ ' developed between '$B$' and '$C$'. The calculation is done in the following steps:
$(i)$ Take current '$I$' entering from '$A$' and assume it to spread over a hemispherical surface in the block.
$(ii)$ Calculatefield $E(r)$ at distance '$r$' from $A$ by using Ohm's law $E = \rho j$, where j is the current per unit area at '$r$'.
$(iii)$ From the '$r$' dependence of $E(r)$, obtain the potential $V(r)$ at $r$.
$(iv)$ Repeat $(i), (ii)$ and $(iii)$ for current '$I$' leaving '$D$' and superpose results for '$A$' and '$D$'.
For current entering at $A$, the electric field at a distance '$r$'
from $A$ is
An ammeter $A$ of finite resistance, and a resistor $R$ are joined in series to an ideal cell $C$. $A$ potentiometer $P$ is joined in parallel to $R$. The ammeter reading is $I_0$ and the potentiometer reading is $V_0$. $P$ is now replaced by a voltmeter of finite resistance. The ammeter reading now is $I$ and the voltmeter reading is $V$.
Assertion : Free electrons always keep on moving in a conductor even then no magnetic force act on them in magnetic field unless a current is passed through it.
Reason : The average velocity of free electron is zero.
A meter bridge is set-up as shown, to determine an unknown resistance ' $X$ ' using a standard $10$ ohm resistor. The galvanometer shows null point when tapping-key is at $52 \ cm$ mark. The end-corrections are $1 \ cm$ and $2 \ cm$ respectively for the ends $A$ and $B$. The determined value of ' $X$ ' is
A cell, shunted by a $8 \; \Omega$ resistance, is balanced across a potentiometer wire of length $3 \; m$. The balancing length is $2 \; m$ when the cell is shunted by $4 \; \Omega$ resistance. The value of internal resistance of the cell will be $\dots \; \Omega .$
Two cells, $e.m.f.$ of each is $E$ and internal resistance $r$ are connected in parallel between the resistance $R$. The maximum energy given to the resistor will be, only when