Describe the low-voltage bulb test for conductors and insulators and its limitation.

Solution & explanation

Insert a test specimen into a small cell-and-lamp circuit with secure contacts. A lit lamp indicates enough current for that lamp, supporting conduction. An unlit lamp may mean an insulator, but may also mean poor contact, an exhausted cell or resistance too high for visible lighting. Check the apparatus with a known conductor and do not infer zero conductivity from darkness alone.