Which description matches a glass tubular fuse?

• A. A small glass tube containing a metal filament
• B. A copper coil inside
• C. A plastic case with a magnet
• D. A ceramic block with a resistor

Answer: (A)

Glass tubular fuses protect circuits by carrying the normal current and then interrupting it when it overheats due to overcurrent. They are built as a small glass tube that contains a metal filament (the fuse element) connected to end caps. When the current exceeds the fuse’s rating, the filament heats up and melts, opening the circuit and preventing damage downstream.

That description matches a small glass tube containing a metal filament. The other options describe different components: a copper coil inside would be a relay coil or solenoid, a plastic case with a magnet points to a magnetic switch or relay, and a ceramic block with a resistor indicates a resistor assembly.