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How to determine P=V^2/R for a lightbulb?
The lightbulb wattage was 53 and according to my multimeter it said the reading was 18@2000. Can anyone help me? I'm SO lost!!!
It says "How well does your computed value agree with the value cited by the bulb manufacturer?" Does that mean it wants me to determine what the wattage would be given my measured resistance reading?
Believe me it makes little sense to me as well! I set it to Ω” @ 2000k on my multimeter and then the reading was too low so I set it to 2000.
3 Answers
- billrussell42Lv 79 years agoFavorite Answer
"the reading was 18@2000."
What reading? Was the multimeter measuring volts or amps or watts?
and what does the @2000 mean? do you mean x 2000 mA or mV? Because your statement makes little sense as it is.
- roderick_youngLv 79 years ago
I'm taking a wild guess that you had your multimeter set on the 2000 ohm range, and measured 18 ohms. That is R, 18 ohms.
Now let's say the voltage across the bulb is 100 volts. Perhaps you measured it earlier. That will be V.
P = (100)^2/18 = 10000/18 = 550 watts!
If this is an incandescent bulb, in reality, the resistance goes up as it gets hot, meaning that the value of R while operating is much, much higher.
- RickLv 79 years ago
I don't know what your meter reading means, but you can't determine the resistance of a light bulb by measuring it when it is cold, because the resistance goes up quite a bit when it is hot.
