Technologies K–10 · Years 5–6

Lighting an LED safely: cells, resistor and switch

Physical World (NSW Science and Technology K–6, 2017); Design and Technologies: Knowledge and understanding, Technologies context: Engineering principles and systems (ACARA v9)

Practical, model not builtLow risk

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

A circuit transfers energy from the cells to the LED, which transforms it into light, and a resistor in the loop limits the current: the larger the resistance, the smaller the current and the dimmer the LED, which also keeps the LED under its current limit.

What you need

2 AA alkaline cells (1.5 V each) in a holder with leads
1 red 5 mm LED (datasheet forward voltage 1.9 V typical, 2.3 V maximum, at 10 mA; 30 mA maximum current, for example Kingbright WP7113ID)
Resistors of 47 Ω, 100 Ω and 220 Ω, 0.25 W
1 slide switch, 6 alligator leads or a breadboard
1 digital multimeter with a 200 mA current range
1 small DC motor and 1 active (self-drive) buzzer rated for 3 V, with its positive lead marked + (it sounds only one way round)

How to do it

Find the LED's longer leg (positive) and the flat edge on its rim (negative).
Build a single loop: cell holder → switch → 100 Ω resistor → LED → back to the cell holder. Switch on.
Measure the cell voltage, then connect the multimeter in series and measure the current.
Predict whether the LED will be brighter or dimmer with the 220 Ω resistor and with the 47 Ω resistor, then swap each in and measure the current.
Turn the LED around and record what happens.
Replace the LED and resistor with the motor, then with the buzzer (its + lead towards the cell holder's positive terminal), and say what the electrical energy becomes each time.

What you should see

With the 100 Ω resistor the simulation's model gives 11.0 mA for the LED's typical 1.9 V with 3.0 V cells, and 7.0 mA if the LED needs its maximum 2.3 V; fresh cells that read above 3.0 V give more, and entering the measured cell voltage in the simulation gives the model's current for those cells. The 220 Ω resistor lets less current through and the LED is dimmer (the model gives 5.0 mA for 1.9 V and 3.2 mA for 2.3 V); the 47 Ω resistor lets more through and the LED is brighter (23.4 mA for 1.9 V and 14.9 mA for 2.3 V). The datasheet specifies both of those forward voltages at 10 mA, and an LED's forward voltage rises as the current rises, so at 47 Ω the measured current sits inside that band rather than at the model's 23.4 mA; every value in the band is under the LED's 30 mA limit. Reversed, the LED stays dark and the meter shows no current (the datasheet allows at most 10 µA of reverse current at 5 V). The motor turns electrical energy into motion and the buzzer into sound; a buzzer connected the wrong way round stays silent. The learner knows it worked when each larger resistor gives a smaller current and a dimmer LED.

What changes

What you change: resistance (47, 100, 220 Ω)
What you measure: current (mA) and LED brightness
What you keep the same: the same cells
the same LED
the same leads and switch

Common misconceptions

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

The battery pushes out the same current whatever is connected (the resistor sets the current).
An LED works either way round (it conducts in one direction only).
Current is used up by the LED so less returns to the cell (the same current flows all the way round the loop).

Safety card

Low riskLearners carry it out

Hazards

A short circuit across the cells makes them hot
An LED without a resistor can be damaged

Controls

Never join the cell terminals directly; switch off before changing parts
Always include a resistor with the LED; alkaline AA cells only, no lithium packs or mains

Note

Low-voltage cells only; no chemicals handled and no heating intended. Record the activity on Primary School RiskAssess (riskassess.com.au).

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), NESA. The syllabus taught in 2026; the 2024 syllabus replaces it from 2027. Code read from the official syllabus document (DOCX) on 2026-09-22.ST3-8PW-ST ST3-2DP-T
Science and Technology K–6 Syllabus (2024), NESA. Implementation from 2027, so this code describes the future syllabus. Code read from the Stage 3 content page on 2026-09-22, where its focus area holds the content group on electrical energy being transferred and transformed.ST3-SCI-01
Science and Technology K–6 Syllabus (2024), NESA. Implementation from 2027, so this code describes the future syllabus. Code read from the Stage 3 content page on 2026-09-22; the entry is a fair test with the variables it lists.ST3-PQU-01
Australian Curriculum v9AC9TDE6K02

Sources

The pages the author read to write this activity.

All Concept Studio activities