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The number of dry cells, each of $e.m.f.$ $1.5\,volt$ and internal resistance $0.5\, ohm$ that must be joined in series with a resistance of $20\, ohm$ so as to send a current of $0.6\,A$ through the circuit is
In the following $'I'$ refers to current and other symbols have their usual meaning, Choose the option that corresponds to the dimensions of electrical conductivity
A potentiometer consists of a wire of length $4\, m$ and resistance $10\,\Omega $. It is connected to a cell of $e.m.f.$ $2\, V$. The potential difference per unit length of the wire will be ............. $V/m$
$\mathrm{A}$ circuit is comprised of eight identical batteries and a resistor $R = 0.8\,\Omega$ . Each battery has an $\mathrm{emf}$ of $1.0\, V$ and internal resistance of $0.2\,\Omega$ . The voltage difference across any of the battery is ............. $V$
An electric toaster has resistance of $60\ \Omega$ at room temperature $\left(27^{\circ} \mathrm{C}\right)$. The toaster is connected to a $220 \mathrm{~V}$ supply. If the current flowing through it reaches $2.75 \mathrm{~A}$, the temperature attained by toaster is around : (if $\alpha=2 \times 10^{-4} /{ }^{\circ} \mathrm{C}$ )
Four wires of the same diameter are connected in turn between two points, maintained at a constant potential difference. Their resistivities are; $\rho $ and $L$ (wire $1$ )., $1.2\,\rho $ and $1.2\,L$ (wire $2$ ), $0.9\,\rho $ and $0.9\,L$ (wire $3$ ) and $\rho $ and $1.5\,L$ (wire $4$ ). Rank the wires according to the rates at which energy is dissipated as heat, greatest first
There is a current of $20$ amperes in a copper wire of ${10^{ - 6}}$ square meter area of cross-section. If the number of free electrons per cubic meter is ${10^{29}}$, then the drift velocity is
$12$ cells each having the same emf are connected in series and are kept in a closed box. Some of the cells are wrongly connected. This battery is connected in series with an ammeter and two cells identical with each other and also identical with the previous cells. The current is $3\, A$ when the external cells aid this battery and is $2\,A$ when the cells oppose the battery. How many cells in the battery are wrongly connected :-
The emf of a battery is $2\, V$ and its internal resistance is $0.5 \,\Omega$. The maximum power which it can deliver to any external circuit will be ............. $watt$