NCEA Level 1 Energy Practice Test

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Why does a greenhouse trap heat?

The glass blocks most infrared radiation.

The air inside is completely still.

The transparent cover prevents solar radiation from entering.

The interior surfaces absorb heat and re-emit infrared slowly.

Heat is trapped because the sun’s energy enters through the transparent cover and warms the interior surfaces. Those surfaces then re-emit heat as infrared radiation, but the glass is not very letting infrared escape quickly. So the interior heats up and holds onto that heat, making the greenhouse warmer than outside. The inside air moving a little or not isn’t the main factor; the crucial part is the warmed surfaces emitting infrared slowly, which prevents heat from escaping efficiently.