Why does a hotter bulb have more resistance?

Electrons need to travel past the metal ions in the filament.
Each time it collides with a metal ion, it loses energy.
This energy is transferred to the metal ion, making it vibrate more.
This makes the wire hotter.
This energy transfer is what we refer to as resistance.
As the wire gets hotter, the metal ions vibrate more.
This makes it harder for the electrons to pass through because there are more frequent collisions between the electrons and the vibrating metal ions.
This means that the resistance of the filament increases as it gets hotter, because the electrons lose more energy.

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