When current is switched 'on' in a room heater, it changes to _________ (red, white) colour.

Hint: Heating effect of electric current is property of the current which states that heat is generated when an electric current is passed through a conductor. This is due to the resistance caused by the conductor to the flowing current, and to overcome this resistance caused by the conductor will generate the heat in that conductor.

Complete answer:
Due to the massive heat generation, when current is switched 'on' in a room heater, its colour changes to red.
Heat generation makes the filament red-hot and makes it look red in colour.

Explanation-
a.)The heating element in the room heater is of a metal like nichrome and the metals like nichrome are very good conductors of electricity and have a high melting point.
b.)Now the heating effect of the electric current will be applied and will produce heat when we start the current to flow.
c.)This generated heat will make the filament glow brighter and brighter and finally it will glow in red colour.

Note:
According to the joule’s law the amount of the heat production in any conductor is directly proportional to the square of the electric current flowing through the conductor.

There are three effects of the electric current that means when a current is flowing through a conductor or any circuit then it will make some effects also. Those effects of the electric current are as follows:
A. Heating effect of the electric current.
B. Chemical effect of the electric current.
C. Magnetic effect of the electric current.