Two bulbs, power, voltage, seres connection

AI Thread Summary
When two bulbs rated 25 W - 110 V and 100 W - 110 V are connected in series to a 230 V supply, the current through each bulb must be the same due to the series configuration. The user initially calculated the current for each bulb incorrectly, leading to confusion about the relationship between voltage, power, and resistance. To find the correct resistance, the user is advised to consider each bulb's specifications at their rated voltage. The resistance can be calculated using the formula p = v²/r, which requires using the rated voltage of 110 V for each bulb. Understanding these calculations is crucial for predicting the behavior of the bulbs under the given conditions.
math_maj0r
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Homework Statement



Two bulbs rated 25 W - 110 V and 100 W - 110 V are connected in series to a 230 V supply. What will happen?
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Homework Equations



p = vi. p = v2/r


The Attempt at a Solution



I am not sure I know how to interpret it correctly. To find the current through bulb 1, I did P1/V1 = 25/110 = .227, and for bulb 2 I did P2/V2 = 100/110 = .909. This can't be right because I1 must equal I2 since they are in series.

If I use the other formula p = v2/r and solve for resistance, i get a really big answer. i think i may be doing something wrong by plugging in 110 for v.

?
 
Physics news on Phys.org
You get a big answer ?
How much ?
 
First, consider each bulb separately.

If you connect the 25W bulb across a 110V source (as it was designed for), what is the resistance?
 

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