Power Delivered and Heat Dissipated in a Circuit

Q. A filament bulb(500w, 100v) is to be used in a 230v main supply. When a resistance R is connected in series, it works perfectly and the bulb consumes 500w. The value of R is

Q. An electric kettle has two coils. When one coil is connected to the AC mains the water in the kettle boils in 10 minutes. When the other coil is used the same quantity of water takes 15 minutes to boil. How long will it take for the same quantity of water to boil if the two coils are connected in parallel?

1. 6 min
2. 12 min
3. 18 min
4. 24 min

Q. A resistor of resistance R is connected to an ideal battery (battery with zero internal resistance). If the value of R is increased, the heat developed in the resistor for equal interval of time will ___.

1. increase
2. decrease
3. remains unchanged
4. Data insufficient

Q. A battery of internal resistance $4\Omega$ is connected to the network of resistances as shown. In order to give the maximum power to the network, the value of $R\left(in\Omega \right)$ should be

1. $\frac{4}{9}$
2. $\frac{8}{9}$
3. 2
4. 18

Q. A cell of emf 8.0 V having a finite resistance of $4\Omega$ is connected to a load resistance of $x\Omega$ for maximum power transfer. The value of $x$ should be

1. 0 ohm
2. 4 ohm
3. 3 ohm
4. 2 ohm

Q. The voltage across a bulb is decreased by $2\%.$ Assuming that the resistance of the filament remains unchanged the power of the bulb will

1. decrease by $2\%$
2. increase by $2\%$
3. decrease by $4\%$
4. increase by $4\%$