Power is maximum when $r = R$ $ \Rightarrow $ ${P_{\max }} = {E^2}/4r$
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$n$ identical cells are joined in series with two cells $A$ and $B$ with reversed polarities. $emf$ of each cell is $E$ and internal resistance is $r$. Potential difference across cell $A$ and $B$ is : $(n > 4)$
An electric kettle has two heating coils. When one coil is used, water in the kettle boils in $5$ minutes, while when second coil is used, same water boils in $10\,\min$. If the two coils, connected in parallel are used simultaneously, the same water will boil in time
A $10\,m$ long potentiometer wire has a potential gradient of $0.0025\, V/cm$. Calculate the distance of null point when the wire is connected to a $1.025\,V$ standard cell ............... $\mathrm{m}$
Voltmeters $V_1$ and $V_2$ are connected in series across a $D.C.$ line. $V_1$ reads $80\, volts$ and has a per volt resistance of $200 \,\Omega$. $V_2$ has a total resistance of $32 \,kilo-ohms$. The line voltage is .............
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 :
Resistances $R_1$ and $R_2$ each $60\,\Omega$ are connected in series as shown in figure. The Potential difference between $A$ and $B$ is kept $120$ volt. Then what ............. $V$ will be the reading of voltmeter connected between the point $C$ and $D$ if resistance of voltmeter is $120\,\Omega .$
Tend identical cells each of potential $E$ and internal resistance $r$ are connected in series to form a closed circuit. An ideal voltmeter connected across three cells, will read $...........E$
If resistance of the filament increases with temperature, what will be power dissipated in a $220\, V- 100\, W$ lamp when connected to $110\, V$ power supply