In india electricity is supplied for domestic use at $220\,\,V$. It is supplied at $110\,\, V$ in $USA$. If resistance of $60\,\, W$ bulb for use in India is $R$, then the resistance of $60\,\, W$ bulb for use in $USA$ will be

Two electric bulbs have tungsten filament of same length. If one of them gives $60\ W$ and the other $100\ W$ , then

Four identical electrical lamps are labelled $1.5\,V$, $0.5\,A$ which describes the condition necessary for them to operate at normal brightness. A $12\,V$ battery of negligible internal resistance is connected to lamps as shown, then

In the circuit shown, the resistance $r$ is a variable resistance. If for $r = fR,$  the heat generation in $r$ is maximum then the value of $f$ is 

A heater coil is cut into two equal parts and only one part is now used in the heater. The heat generated will now be

An electric bulb rated for $500\, watts$ at $100\, volts$ is used in a circuit having a $200-volt$ supply. The resistance $R$ that must be put in series with the bulb, so that the bulb draws $500\, W$ is .................. $\Omega$