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Q & A: Current limitations of fruit batteries.

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Most recent answer: 03/24/2013
Q:
I have a series of fruit hooked together in a circuit that has a voltage of 15.79 . I tried to light a 12volt 15 watt light bulb and it will not light up the bulb. What is the problem.
- Layne (age 11)
Somerville, Texas. USA
A:
Hello Layne
You probably have heard of Ohm's law,   V = I R, where V is the voltage, I is the current and R is the resistance of the circuit.   Rearranging this equation you get I = V/R.   Now the amount of current required to light up a 12 Volt, 15 Watt light bulb is I =  W/V = 15/12 = 1.25 Amperes. That's a lot!   There is no way you can get this amount of current from a fruit battery because the internal resistance of the battery is too big and limits the available current.    
You can make a little experiment to investigate this.  Instead of connecting a light bulb, connect various values of resistors and measure the resulting voltage across the resistor.

LeeH

(published on 03/24/2013)

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