According to Wien’s law the relation between temperature T of a cavity radiator and the wavelength at which it radiates most strongly is

.

The microwave background radiation peaks in intensity at a wavelength of 1.1 mm. (a) We have to find the temperature to which it corresponds. (b) About 300,000 y after the Big Bang, the universe became transparent to electromagnetic radiation. Its temperature then was about . We have to find the wavelength at which the background radiation was then most intense.

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(a)

According to Wien’s law the relation between temperature T of a cavity radiator and the wavelength at which it radiates most strongly is

.

The microwave background radiation peaks in intensity at a wavelength of 1.1 mm. Therefore, from Wien’s law we note that the temperature of the universe then was

(b)

About 300,000 y after the Big Bang, the universe became transparent to electromagnetic radiation. Its temperature then was about . The wavelength at which the background radiation was then most intense was