Three equal resistors connected in series across a source of e.m.f. together dissipate ${\rm{10}}\,\,{\rm{watt}}$. If the same resistors are connected in parallel across the same e.m.f., then the power dissipated will be

The current flowing through a resistor $R$ varies with time $t$ as $I = at - bt^2$, where $a$ and $b$ are positive constants. The total heat produced in $R$ is:

Two bulbs of ${\rm{100}}\,\,{\rm{watt}}$ and ${\rm{200}}\,\,{\rm{watt}}$ working at ${\rm{220}}\,\,{\rm{V}}$ are joined in series with ${\rm{220}}\,\,{\rm{V}}$ supply. Total power consumed will be

A heating coil can heat the water of a vessel from 20\,{\,^0}{\rm{C}} to 60\,{\,^0}{\rm{C}} in $30\,\,minutes$. Two such heating coils are put in series and then used to heat the same amount of water through the same temperature range. The time taken now will be (neglecting thermal capacity of the coils)

An electric water kettle rated ${\rm{2}}{\rm{.1 }}\,{\rm{kW}}$ is filled with ${\rm{1}}{\rm{.5 }}\,\,{\rm{kg}}$ of water at 20\,{\,^0}{\rm{C}}. How many seconds does it take to reach the boiling point of water? Assume that there are no heat losses from the kettle. Specific heat capacity of water is $4200\,\,{\rm{Jk}}{{\rm{g}}^{ - 1}}\,{{\rm{K}}^{ - 1}}$

If an electric current is passed through a nerve of a man, then man

A current $i$ passes through a wire of length $l$, radius of cross-section $r$ and resistivity $\rho$. The rate of heat generation is

When two resistances ${R_1}$ and ${R_2}$ are connected in series and parallel with $120\,\,V$ line power consumed will be $25\,\,W$ and $100\,\,W$ respectively. Then the ratio of power consumed by ${R_1}$ to that consumed by ${R_2}$ will be

A silver and a zinc voltmeter are connected in series and a current $I$ is passed through them for a time $t$, liberating w gram of zinc. The weight of silver deposited is nearly

Two filaments of same length are connected first in series and then in parallel. For the same amount of main current flowing the ratio of the heat produced is

Two bulbs, one of $50\,\,watt$ and another of $25\,\,watt$ are connected in series to the mains. The ratio of the currents through them is