# $V = 4 volts$ but $I = 0$

Recently in my school, I tried to generate electricity from plants in a flower pot with copper and Zinc electrodes. The Potential difference in the voltmeter read 2 to 3 volts but when I connected the a small motor to it , it did not work. Though Potential difference was produced, there was no current. What could be the reason? How can I solve this problem and rotate the motor?

• Change your motor and re-examine the process – Raihan Amin Dec 12 '18 at 2:15
• @RaihanAmin Changing the motor is most likely not going to help. – Pieter Dec 12 '18 at 7:15

I don't agree with the above answer, sorry EUGenius. The reason is the battery cannot produce enough electrons (current) and the motor shorts it out, there is a small amount of current but not enough. And more water to the pot and use a bigger surface area of metal, add lemon juice but it might harm the plant. See lemon battery in google.

• No harm in trying to measure the resistance to see if it's high. Or too low. If the motor shorts it out, probably more amperage won't help. But it's interesting. People want to use Ohm's law. If you know the voltage and the resistance, then you know the amperage. But if the battery just can't produce that much, then I guess the voltage will quickly fall. And then if you open the circuit, the battery might slowly restore itself, and might at some point reach 4 volts again. It isn't enough to take a couple of measurements and use the formula. – J Thomas Dec 12 '18 at 3:33
• This is described by assigning a large internal resistance to the "battery" (the electrodes in the flower pot). – Pieter Dec 12 '18 at 7:13

Ajit,

Power (P) = Voltage (V) x Current (I)

Since Voltage (V) = Current (I) x Resistance (R),

therefore

Power (P) = Voltage (V) ^ 2 / Resistance (R)

Since the power seems to be negligible, but there is a voltage present, this means:

0 = V^2 / R

or

0 = I^2 x R

Therefore your resistance must be extremely high for this to happen. Also, you do need a certain minimum power in order to start operating the motor. To increase your power, you could either increase the current (by adding more electrodes, increase the concentration of flower pots, etc.) or decrease the resistance in your circuit (by using more conductive wires).

• The wires are not the problem. – Pieter Dec 12 '18 at 7:14