Resistance $n$,each of $r \ \Omega$,when connected in parallel give an equivalent resistance of $R \ \Omega$. If these resistances were connected in series,the combination would have a resistance in $\Omega$,equal to

An electric kettle has two heating coils. When one of the coils is connected to an a.c. source,the water in the kettle boils in $10$ minutes. When the other coil is used,the water boils in $40$ minutes. If both the coils are connected in parallel,the time taken by the same quantity of water to boil will be ...... $min$.

What is the effective resistance between $A$ and $B$ in the given figure (in $\Omega$)?

$A$ wire is broken into four equal parts. $A$ packet is formed by keeping the four wires together. The resistance of the packet in comparison to the resistance of the original wire will be:

An electric heater and an electric bulb are rated $500\, W, 220\, V$ and $100\, W, 220\, V$ respectively. Both are connected in series to a $220\, V$ $a.c.$ mains. The current in the circuit when both are connected in series is ................ $A$.

The power consumed when $10 \ V$ voltage is applied to a series combination of $10$ resistors of each $1 \ \Omega$ is $P_{s}$ and the power consumed when the same $10 \ V$ is applied to the parallel combination of these $10$ resistors is $P_p$. The value of $\frac{P_{s}}{P_{p}}$ is