# Explain why the intensity of radiation emitted by the Earth's surface is predominantly in the infrared region of the electromagnetic spectrum, whilst the radiation received from the Sun is predominantly in the visible region.

> IB DP Physics Standard Level (2023 syllabus) — B.2 Greenhouse effect · Explain · 4 marks

> The Sun has a surface temperature of approximately 5800 K. The Earth's surface has an average temperature of approximately 288 K.

## Mark scheme (4 marks)

1. All bodies emit radiation with a peak wavelength that depends on their temperature (Wien's displacement law / blackbody radiation principle).
2. The Sun's high temperature (~5800 K) means its peak emission wavelength falls in the visible region of the spectrum.
3. The Earth's much lower surface temperature (~288 K) means its peak emission wavelength is much longer, falling in the infrared region.
4. Peak wavelength and temperature are inversely proportional, so the much lower Earth temperature produces a peak wavelength roughly 20 times longer than the Sun's peak wavelength.

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