What it does
Electricity flows only around a closed circuit: from the cell, through the wires and the bulb, and back. This page gives you a simple circuit with a gap in it. Put a material in the gap, press Switch on, and see whether the bulb glows. If it does, the material is a conductor; if it stays dark, it is an insulator (or a very poor conductor). Swap the torch bulb for an LED tester: an LED lights up with a much smaller current, so it can show weak conductors like salt water, lemon juice and even tap water that a bulb cannot. Every test you make is added to a results table.
It follows the school topics Class 8 Science, electricity (circuits, conductors and insulators, and how liquids such as salt water conduct) and Class 10 Physics, electricity (resistance and resistivity). Next, the ohm's law lab measures current against voltage, and series and parallel connects several bulbs; the fair test planner helps you plan your own conductor test.
How to use it
- Choose a tester: a torch bulb or an LED. Choose 1 cell or 2 cells.
- Tap a material to put it in the gap at the bottom of the circuit.
- Press Switch on (or tap the switch in the picture). Read whether it glows brightly, dimly, faintly or not at all.
- Try each material and read the results table.
- The Level switch (Class 10) shows the sample’s resistance from R = ρL/A (a 5 cm strip of 1 mm² for solids, 5 cm of liquid 1 cm² across) and the current.
Worked example
With 2 cells (3 V) and the torch bulb, a copper strip has R = 1.68 × 10⁻⁸ × 0.05 ÷ 10⁻⁶ = 0.00084 Ω, so the current is 3 ÷ 8.33 = 0.36 A and the bulb glows brightly. Salt water between two nails has R = 0.2 × 0.05 ÷ 10⁻⁴ = 100 Ω. The current is 3 ÷ (8.33 + 100) = 27.7 mA, far too small for the bulb, which stays almost dark. With the LED tester the current is (3 − 1.8) ÷ (100 + 100) = 6 mA, and the LED glows brightly. A plastic ruler lets through only about 10⁻¹⁴ A: nothing at all.
Check yourself
Five fresh questions: picking a conductor, why wires have plastic covers, why an LED shows weak conductors, Ohm’s law and R = ρL/A. Nothing is saved.
Tips
- Metals are good conductors; graphite (pencil lead) is the odd non-metal that conducts.
- Pure water hardly conducts. Water from taps, rivers and our bodies has dissolved salts in it, which is why wet hands and electricity are dangerous.
- An LED needs about 1.8 V just to start glowing, so one 1.5 V cell cannot light it.
FAQ
Can I test these at home? Use only a torch cell or two, never mains electricity or a wall socket.
Why does the bulb glow more with two cells? Twice the voltage pushes more current through, and the bulb’s power rises with the current squared.
Is this from NCERT? No. It is an independent study aid that follows the same school topics, with its own pictures and numbers.
Where the numbers come from
- Resistance R = ρL/A, Ohm's law I = V/R, power P = I²R, and a 1.5 V cell, a 2.5 V 0.3 A torch bulb and an LED with about 1.8 V across it: standard school physics.
- Resistivities are rounded typical room-temperature values from general physics knowledge (metals to three figures, poor conductors and insulators only to the nearest power of ten, as they vary a lot between samples).
- Checked by hand: resistance, current and glow level for every material with each tester and cell count.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
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Last updated 2026-11-09.