A piece of red glass is heated until it glows in an otherwise dark room. What colour does it appear to glow?

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1. A piece of red glass is heated until it glows in an otherwise dark room. What colour does it appear to glow?

Green

Purple

Black

Yellow

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Red glass looks red normally because it mainly transmits red light while absorbing other colours strongly. By Kirchhoff’s Law, a strong absorber is also a strong emitter, so when heated and glowing, it emits most strongly in the colour it usually absorbs — appearing green.