Science and Technology K–6 · Year 6

Lemon cells: chemical energy into electrical energy

Science understanding: Physical sciences

PracticalLow risk

The idea

Two different metals in an acidic fruit make a cell that transforms chemical energy into electrical energy; one cell gives less than 1 V and a tiny current, so cells are joined in series to light an LED.

What you need

4 lemons, each rolled firmly on the bench to free the juice
4 galvanised (zinc-coated) nails about 5 cm long, or zinc strips
5 copper strips or 5 cm lengths of thick bare copper wire
5 leads with alligator clips
a digital multimeter (20 V dc range and 2 mA or 200 mA dc range)
1 red LED
1 torch globe rated 2.5 V 0.3 A for comparison
a potato and an apple for the extension

How to do it

Push a zinc nail and a copper strip 3 cm deep into a lemon, 3 cm apart and not touching. Measure the voltage between them.
Put two copper strips in a second lemon and measure the voltage: this is the control with only one metal.
Set the meter to its current range and measure the current the single lemon cell drives through the meter.
Join 2, 3 and then 4 lemon cells in series (the copper of one lemon to the zinc of the next) and measure the total voltage each time.
Connect the LED across 1, 2, 3 and 4 cells in a darkened room (long leg to the copper end) and record when it first glows. Try the globe across 4 cells.
Replace one lemon with the potato, then the apple, and compare the voltages.
Graph total voltage against number of cells.

What you should see

One lemon cell reads less than 1 V, while two copper strips read almost 0 V: two different metals are needed. The current is about 1 mA or less. Voltages add in series, so at about 0.8 V a lemon, 2 cells give about 1.6 V, 3 cells about 2.4 V and 4 cells about 3.2 V; a red LED needs about 2 V, so it glows faintly only with 3 or 4 cells joined. The globe stays dark even on 4 cells because it needs 0.3 A, hundreds of times more than the lemons supply. In October 2021 Saiful Islam and the Royal Society of Chemistry set a Guinness World Record with a lemon battery of 2,923 lemons that reached 2,307.8 V, which works out at 0.79 V a lemon, and the record page also gives a current of 0.84 mA. Multiplying the two into the 1.94 W that page quotes overstates what such a battery can deliver: a voltage read with almost nothing drawing current and a current read through a far lower resistance do not happen at the same time, which is the lesson of the globe that stays dark on four lemons. The zinc slowly reacts away: a chemical change supplies the energy.

What changes

What you change: number of cells in series (and the fruit or vegetable used)
What you measure: total voltage and whether the LED lights
What you keep the same: same metals
electrode depth and spacing
same meter
fruit rolled the same way

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

The electricity is stored in the lemon juice (it comes from the zinc reacting).
Any two nails will work (two of the same metal give almost no voltage).
A high enough voltage will light anything (the current is too small for a globe).

Safety card

Low riskLearners carry it out

Hazards

sharp nails
lemon juice stings cuts and eyes
fruit contaminated with zinc

Controls

an adult starts the nails in firm fruit
fruit and vegetables thrown away after use, never eaten
wash hands afterwards

Note

Risk assessment before the lesson using Primary RiskAssess or the school's own template.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science and Technology K-6 Syllabus (2017), current, taught until 2026; code read from the syllabus document on 22 September 2026ST3-8PW-ST ST3-1WS-S
Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; Stage 3 content: 'Recognise that an electrical circuit transfers electrical energy from a source, through a pathway, to a device that transforms electrical energy into other forms of energy', which sits in the focus area whose knowledge outcome is this one; code read from the outcomes page and the content read from the Stage 3 content page on 23 September 2026ST3-SCI-01
Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; code read from the outcomes page on 22 September 2026ST3-PQU-01 ST3-DAT-01
Australian Curriculum v9AC9S6U03AC9S6I02AC9S6I03AC9S6I04

Sources

The pages the author read to write this activity.

All Concept Studio activities