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I’m super stuck.

The first question was about finding the current which I managed to get and it was 0.75Amps then, the second was looking for the voltage of the resistor then the third one was looking for the resistance.

I can’t remember the power of the lamps (I know I’m useless) but if I learn how to find the voltage of the resistor if you only have the current and the supply voltage and supply power or the power and voltage of the lamps I will be able to do it.

If anyone could help that would be brilliant.

I’m super stuck. The first question was about finding the current which I managed-example-1

1 Answer

4 votes

The voltage all the way around the loop ... between the terminals of the battery ... is 36 volts total. It looks like 12 of those volts are across one lamp, and 12 of them are across the other lamp. That leaves the last 12 volts unaccounted for, and only one more component in the loop (the resistor), so the remaining 12 volts is across the resistor.

So far, we don't have enough information to calculate any current in the loop, or the power dissipated by any component. To go any farther, we'll need to take your word for it ... the current in the loop is 0.75 Ampere. Fine !

In a resistor . . . Resistance = (voltage) / (current)

Resistance = (12 volts) / (0.75 Amp) = 16 ohms .

Power dissipated by anything = (voltage across it) x (current through it).

Power dissipated by the resistor OR either lamp =

(12 volts) x (0.75 Amp) = 9 watts .

That's not a lot for a light bulb, but it IS for a resistor. That baby has to be physically large (maybe like a lipstick), and cooled ... attached to a heatsink, or air blowing over it, or water flowing over it.

PS: I hope you're right about that 0.75 Amp.


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