Question

Astronomy Question:

1.Relate the peak of a thermal radiation spectrum to temperature.

2.Predict and interpret the effects of Doppler shift.

3.Use the inverse square law equation to relate brightness and luminosity.

Answer 1

1.

The wavelength () of radiation having maximum intensity can be used to determine the absolute temperature (T) with the help of Wien's displacement law.

It simply means that both the values are inversely proportional to each other.

2.

As we know already, if the bodies are approaching, then the observer will experience more frequency than original.
As a result, the colour of the radiation will also change, as colour depends on frequency.
Increase in frequency means colour shifts towards violet or blue end of the spectrum. This is called blueshift.

Similarly, bodies moving away from each other will experience redshift.

3.

Brightness is inversely proportional to square of the distance from the source.

b = k/d^2

This k depends upon the energy of the star.If L is the energy emitted by star per unit time, it gets spread in all directions. Hence, it needs to be divided with 4pi. 4pi steradian means spherical surface.

As L depends on the source, which is a star, it remains constant.

so, k = L/4pi

Hence, we can say