(d) Cosmology ​

What is the doppler effect?

• The apparent change in frequency is called the doppler effect.
• The doppler effect is the property of all waves.
• Due to doppler effect, the frequency and wavelength of light wave changes and then the light wave changes its colour in its spectrum.

Define redshift and blueshift.

• Redshift indicates that the source of the light wave is moving away from the observer. Almost all the galaxies emit light with redshift.
• The further away a galaxy is, the greater the redshift and therefore the faster it is moving away from us.
• The frequency of light decreases and wavelength increases.

Fig: Redshift

Fig: blueshift

• Blue shift indicates that the source of light wave is moving towards the observer.
• The frequency of light increases and wavelength decreases.

What is Big Bang Theory?

Scientists believe that the universe is expanding with time. In the past, all the matter in the universe was in one place just before an explosion. This theory is called the Big Bang Theory.

Write down the doppler equation

Define Cosmic Microwave Background (CMB) radiation.

According to the Big Bang Theory, the universe is expanding with time and it releases energy. This energy is released in the form of wave. The wavelength of this wave is longer than before. The wavelength is in the microwave part of the electromagnetic spectrum. This microwave radiation is detected in all directions in the universe. This is known as Cosmic Microwave Background radiation.