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

- 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

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)*