Close the loop
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Path: open
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Choose your parts, then press Check.
Live brightness chart
The physics
A bulb needs a closed circuit and conducting parts.
Metals usually let electric current flow. Plastic, dry rubber and dry wood are insulators.
More batteries can make a bulb brighter in this simple model. Do not mix batteries in real experiments.
Brightness is a relative model: bulb power grows with the square of the voltage, so 2 cells give about 4× and 3 cells about 9× the brightness of 1 cell.