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# Physics equation watch

1. I have this question that's got me completely stumped..
Resistors have different power ratings. The most commonly used carbon film resistors have a power rating of 0.25W. calculate the maximum current allowable for a 4.7 ohm resistor.

I have worked it out like this but i know its wrong! :
I = 0.25 / 4.7 = 0.05319 x 0.05319

thanks for the help guys x
2. (Original post by smellybelly1991)
I have this question that's got me completely stumped..
Resistors have different power ratings. The most commonly used carbon film resistors have a power rating of 0.25W. calculate the maximum current allowable for a 4.7 ohm resistor.

I have worked it out like this but i know its wrong! :
I = 0.25 / 4.7 = 0.05319 x 0.05319

thanks for the help guys x
P=I2 R

I2=P/R

I=sqrt(P/R)
=sqrt(0.25/4.7)
=sqrt(0.0532) *3sf is enough... those resistors are probably 5% tolerance anyway
=0.231

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