Power is maximum when $r = R$ $ \Rightarrow $ ${P_{\max }} = {E^2}/4r$
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A $2\, volt$ battery, a $15\,\Omega $ resistor and a potentiometer of $100\, cm$ length, all are connected in series. If the resistance of potentiometer wire is $5\,\Omega $, then the potential gradient of the potentiometer wire is ............... $V/cm$
Figure shows a thick shell made of electrical conductivity $\sigma$ and has inner & outer radii of $10\ cm$ & $20\ cm$ respectively and is filled with ice inside it. Its inside and outside surface are kept at different potentials by a battery of internal resistance $\frac{2}{\pi} \Omega \ \&\ \epsilon = 5V$. Find value of $\sigma$ for which ice melts at maximum possible rate if $25\%$ of heat generated by shell due to joule heating is used to melt ice.
A battery is charged at a potential of $15\, V$ for $8$ hours when the current flowing is $10\, A$. The battery on discharge supplies a current of $5\, A$ for $15$ hours. The mean terminal voltage during discharge is $14\, V$. The "Watt-hour" efficiency of the battery is .............. $\%$
Two electric bulbs whose resistances are in the ratio of $1 : 2$ are connected in parallel to a constant voltage source. The powers dissipated in them have the ratio