Three voltmeters, all having different internal resistances are joined as shown in figure. When some potential difference is applied across $\mathrm{A}$ and $B$, their readings are $V_1, V_2$ and $V_3$. Choose the correct option.
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A resistor develops $500\, J$ of thermal energy in $20 \,s$ when a current of $1.5\, A$ is passed through it. If the current is increased from $1.5 \,A$ to $3\, A$ what will be the energy (in $J$) developed in $20\, s$.
The following circuit consist of a $5 \,\mu F$ capacitor, having charge $50 \,\mu C$ as shown. The switch is closed at $t=0$. The value of current in $2 \,M \Omega$ resistor at $t=0$ is ........... $\mu A$
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
The drift velocity of free electrons in a conductor is ‘$v$’ when a current ‘$i$’ is flowing in it. If both the radius and current are doubled, then drift velocity will be
Two conductors have the same resistances at $0^{\circ} \mathrm{C}$ but their temperature coefficients of resistance are $\alpha_1$ and $\alpha_2$. The respective temperature coefficients for their series and parallel combinations are :
Figure shows a simple potentiometer circuit for measuring a small $e.m.f$. produced by a thermocouple. The meter wire $PQ$ has a resistance $5 \,\Omega$ and the driver cell has an e.m.f. of $2\, V$. If a balance point is obtained $0.600\, m$ along $PQ$ when measuring an e.m.f. of $6.00\, mV$, what is the value of resistance $R$ ............... $\Omega$