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As shown in the figure, a potentiometer wire of resistance $20\,\Omega$ and length $300\,cm$ is connected with resistance box (R.B.) and a standard cell of emf $4\,V$. For a resistance ' $R$ ' of resistance box introduced into the circuit, the null point for a cell of $20\,mV$ is found to be $60\,cm$. The value of ' $R$ ' is $.....\Omega$
Two wires $A$ and $B$ of the same material, having radii in the ratio $1: 2$ carry currents in the ratio $4: 1$. The ratio of drift speed of electrons in $A$ and $B$ is
Two coils require $20$ minutes and $60$ minutes respectively to produce same amount of heat energy when connected separately to the same source. If they are connected in parallel arrangement to the same source; the time required to produce same amount of heat by the combination of coils, will be________ $min$
In this figure the resistance of the coil of galvanometer $G$ is $2\,\Omega$. The emf of the cell is $4\,V$. The ratio of potential difference across $C_1$ and $C_2$ is:
Two electric bulbs marked $40\,W,$ $220\,V$ and $60\,W,\,\,220\,V$ when connected in series across same voltage supply of $220\,V,$ the effective power is $P_1$ and when connected in parallel, the effective power is $P_2.$ Then $\frac {P_1}{P_2}$ is
$A, \,B$ and $C$ are voltmeters of resistance $R, \,1 .5R$ and $3R$ respectively as shown in the figure. When some potential difference is applied between $X$ and $Y,$ the voltmeter readings are $V_A, \,V_B$ and $V_C$ respectively. Then
Two wires of resistance $R_1$ and $R_2$ have temperature coefficient of resistance ${\alpha _1\,}{\rm{ and \,}}{\alpha _2}$, respectively. These are joined in series. The effective temperature coefficient of resistance is