When an electric current passes through a filament, its temperature increases significantly due to electrical (Joule) heating, often until it glows red or white hot in a bulb.

Quick Scoop

  • The filament has electrical resistance, so when current flows, electrical energy is converted into heat (Joule heating).
  • As it heats up, the temperature of the filament rises sharply, which is why a filament lamp becomes very hot and starts to glow.
  • At higher temperatures, the metal atoms in the filament vibrate more, making it harder for electrons to move, so the resistance of the filament also increases with temperature.

What actually happens inside

  • In a typical filament (like tungsten in an incandescent bulb), the narrow wire offers resistance to the moving electrons.
  • The “friction‑like” effect between electrons and vibrating metal ions turns electrical energy into heat, causing the filament temperature to rise to thousands of degrees Celsius in normal operation.

Why the lamp glows

  • Once the filament is hot enough, it emits visible light as thermal radiation, which is why incandescent lamps glow when current flows.
  • If the current (and thus temperature) becomes too high, the filament can overheat, weaken, and eventually melt or break.

In simple exam language

  • Temperature of filament when current passes through it: It increases (it gets very hot and glows).

SEO note / meta description:
When an electric current passes through a filament, its temperature increases due to Joule heating, making it hot enough to glow and increasing its resistance as the temperature rises.

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