Question

A 60 w lightbulb and a 100 w lightbulb are placed one after the other in a circuit. Which bulb is brighter?

Answer 1

Since power determines brightness, wouldn't the 100 W lightbulb glow the brightest?

Answer 2

They'll have the same current running through them, so from \(\large P = I^2 R\), the one that has higher resistance will have the higher power rating

Answer 3

Ok so using that equation, and current is the same in series, the 100 watt one?

Answer 4

lol I'm doing something wrong

Answer 5

You could find the resistance of them numerically. Use P = IV.

For the 100W:
Let's say it's 240V.
The current must be 0.416A.
Then you can find R from V = IR, so R = 576 ohms.

For the 60W:
Let's say it's 240V.
The current must be 0.25A.
Then you can find R from V = IR, so R = 960 ohms.

Answer 6

That's for them in a single circuit, btw.

Answer 7

Oh ok because in a series, the current will be the same.

Answer 8

I was about to get all confused lol

Answer 9

So basically higher power lightbulb means lower resistance.

Answer 10

Thanks

Answer 11

Which makes sense intuitively... if you increase resistance, current drops, which means lower power - since power is I^2 R, so since I is squared, a decrease in I, along with an increase in R, means power still drops because I^2 has a bigger impact.

Answer 12

Yes it makes so much sense! :D