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Temperature and resistance?
At 20°C the carbon resistor in an electric circuit connected to a 4.0 V battery has a resistance of 154 ohms. What is the current in the circuit when the temperature of the carbon rises to 86°C?
I don't know what step I'm missing... I'm confused!
1 Answer
- flutzpahLv 51 decade agoFavorite Answer
Likely there's a table of resistances for carbon resistors in your textbook, or an estimate of resistance vs. temperature for carbon. It is very likely that the resistance goes up as the temperature goes up, and therefore the current ( I ~ V/R, roughly) should go down.
For carbon resistors in that resistance range, the temperature coefficient is about 0.065%/deg. C. That means that a rise of 66 deg. C would lead to an increase of about 66*0.065% ~ 4.29%; this is around 6.6 Ohms for the 154 Ohm resistor, so the new resistance is about 160.6 Ohms.
The new current should be around I = 4.0V/161 Ohm ~ 0.025A, or 25 mA.
This is a guess as to the temperature coefficient for the resistor, though, and you should use what your book tells you.