Grade 10 · ⚛️ Physics · Electricity
Light an LED with a lemon battery
Turn lemons, coins and nails into a battery and measure how connecting cells in series raises the voltage.
Why this matters
Many rural homes in Ethiopia still depend on dry-cell batteries for torches and radios. Every one of those batteries works on the same principle as your lemon: two different metals in a conducting liquid. Understanding cells is the first step toward the solar and battery storage systems now spreading across the country.
Watch the demo
Video coming soon
We're recording a demo for this experiment. Until then, follow the step-by-step guide below.
The science
How a simple cell works
Two different metals (electrodes) placed in a conducting liquid (electrolyte) create a voltage. Zinc gives up electrons more easily than copper, so electrons flow from the zinc through the wire to the copper.
Cells in series
Connecting cells in series (copper of one to zinc of the next) adds their voltages: V_total = V₁ + V₂ + …. One lemon gives about 0.9 V; a red LED needs about 1.8–2 V.
You'll need
- 3–4 lemons↳ Potatoes or salt water in cups also work
- 3–4 galvanized (zinc-coated) nails or screws
- 3–4 copper pieces: copper coins, or bare copper wire
- Short wires or wires with crocodile clips
- A small red LED↳ From an electronics shop, or salvaged from an old toy
- A multimeter if you have one (optional)
Safety first
- This experiment uses only very low voltages and is safe. Never connect anything to a wall socket.
- Don't eat the lemons afterwards — metal ions dissolve into the juice.
Step by step
0/5 doneWhat you should see
One lemon alone gives about 0.9 V, which is not enough to light the LED. With three or four lemons in series, the LED glows faintly — best seen in a dark room.
Why it happens
Zinc reacts with the acid in the lemon juice and releases electrons, which travel through the wire to the copper. Each lemon cell provides a small voltage; connecting them in series adds those voltages until they are high enough to push current through the LED.
Didn't work? Try this
The LED doesn't light at all.
Flip the LED around — it only works in one direction. Then check that no nail touches a copper piece inside the lemon.
My multimeter reads 0 V.
Your nail may not be zinc-coated. Use galvanized nails (dull grey) and clean the copper with salt and vinegar.
The LED is very dim.
Add another lemon in series, and look in a darkened room.
Still stuck? Ask the lab assistant
Check your understanding
1. Why do you need two different metals?
2. Three cells of 0.9 V are connected in series. What is the total voltage?
Your lab notebook
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