Physics Circuit Problem?

In a simple cct like this the lamp and resistor are both giving off power in the form of heat. The lamp has 30V across it and so the resistor must have the other 90V across it. Using Power = current times voltage and transposing to Power divided by Voltage = Current (P/V=I) then 50/30=1.667 Amps. This current is also flowing through the resistor, using Ohm's law V=IR then R=V/I equals 90/1.667=54 Ohm's! Hope this is of some help.

Edit: The cct works as a voltage divider and because everything is in series then the source voltage must be divided in proportion to the resistance of the 2 objects in its path. The ratio of the voltage across each will be the same ratio as for the power they each dissipate because they both have the same current running through them.

volage supplied by source = 120 V

Resistor and lamp will distribute this voltage among themselves due to series connection,

In question it is given that , voltage across lamp is is 30 V.

Then remaining voltage for resistor = 120 -- 30 = 90 V

Power of resistor = 50 W

Resistance R = square of voltage / power

= (90 x 90) / 50

= 8100 / 50 =162 ohm

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Abhishek Rathod