# isaac physics bulbs and power question help!

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#1
Looking for any guidance in tackling this question - I’ve tried it a few times but always end up with two unknowns instead of one.

In the circuit below, a bulb is in parallel with a resistor and with the pair then in series with an identical resistor. This is connected to a voltage source which gives a potential of V=230V. The resistance of the bulb is Rb =10.0Ω.

Assume that the bulb is ohmic such that its resistance is constant and does not depend on the current flowing through it, unlike a real filament bulb.

What must R be in order for the power dissipated in the bulb to be 100W?
Last edited by abisola_a; 4 weeks ago
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4 weeks ago
#2
You can start by finding the total current in the main circuit loop (call it I_t) by using Ohm's law and the formulae for resistors in parallel and series. Then, find the proportion of that current passing through the bulb (call it I_b). Power dissipated in bulb is then given by I^2R - set equal to 100 W and solve for R.

Solution attached if you need some hints.
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#3
(Original post by lordaxil)
You can start by finding the total current in the main circuit loop (call it I_t) by using Ohm's law and the formulae for resistors in parallel and series. Then, find the proportion of that current passing through the bulb (call it I_b). Power dissipated in bulb is then given by I^2R - set equal to 100 W and solve for R.

Solution attached if you need some hints.
Thank you so much for your help. I finally managed to work through the question and got the right answer.
Last edited by abisola_a; 4 weeks ago
0
4 weeks ago
#4
Good.
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