When a bulb is switched on, it gives out light and heat. Is it a chemical change or a physical change? Why?
It is aphysical change as when electricity is supplied to the bulb, the electrons jump to a higher energy state. When they come back to their level, it emits energy which falls in the visible region of light. The atoms of the filament (Tungsten) aren't going through any change, that changes their chemical properties. Tungsten is still Tungsten!