At room temperature, copper has free electron density of $8.4 \times {10^{28}}$ per ${m^3}$. The copper conductor has a cross-section of $10^{-6} \,m^2$ and carries a current of $5.4\, A$. The electron drift velocity in copper is
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Two wires of equal diameters, of resistivities ${\rho _1}$ and ${\rho _2}$ and lengths $l_1$ and $l_2$, respectively, are joined in series. The equivalent resistivity of the combination is
Figure $(i)$ below shows a Wheatstone's bridge in which $P, Q, R$ and $S$ are fixed resistances, $G$ is a galvanometer and $B$ is a battery. For this particular case, the galvanometer shows zero deflection. Now, only the positions of $B$ and $G$ are interchanged, as shown in figure $(ii)$. The new deflection of the galvanometer
Two cells of same emf but different internal resistances $I_{1}$ and $I_{2}$ are connected in series with a resistance $R$. The value of resistance $R$, for which the potential difference across second cell is zero, is
A $d.c.$ main supply of $e.m.f.\, 220\, V$ is connected across a storage battery of $e.m.f.\, 200\, V$ through a resistance of $1\,\Omega $. The battery terminals are connected to an external resistance $'R'$ . The minimum value of $'R'$, so that a current passes through the battery to charge it is ............... $\Omega$
Three light bulbs of $40\, W$, $60\, W$ and $100\, W$ are connected in series with $220\, V$ source. Which one of the bulbs will glow brightest ............ $W$