Doppler shift and Popular Inversion question

[Eng student]

Hi, I've got a multiple choice piece of work to do with some questions I cannot figure out. They are:

In regards to red shift, which one is Doppler shift defined as:

1. The increase in wavelength due to Doppler shift, of spectral lines from SPONTANEOUS photon emission from elements on cosmic bodies retreating from the earth
OR
2. The increase in wavelength due to Doppler shift, of spectral lines from STIMULATED photon emission from elements on cosmic bodies retreating from the earth


I’m guessing it is answer 1, spontaneous photon emission. Can someone confirm?andIn regards to Population inversion how can this be achieved practically?

1. Injection of energy from an external source
2. Increase the number of free electrons in a solid
3. By stimulation of emission of light in a gas

I'm 95% certain it is answer 1 but just need confirmation.


Lasers emit intense light due to:

1. Every photon being of the same wavelenth
2. Laser light does not diverge
3. Population inversion implies many photos are emitted per second
4. The frequency of laser light can be controlled
5. Laser light is in the visible spectrum.

I know it is not answer 5. I know that the photons in laser light are f the same frequency and wavelength, and that intensity of light is somewhat dependent on wavelenght.

So I'm guessing it is answer 1 or answer 3, but most likely answer 3.
Thanks

 

[Valkarie]

for your questions! The correct answers are: In regards to red shift, which one is Doppler shift defined as:1. The increase in wavelength due to Doppler shift, of spectral lines from SPONTANEOUS photon emission from elements on cosmic bodies retreating from the earthIn regards to Population inversion how can this be achieved practically?3. By stimulation of emission of light in a gasLasers emit intense light due to:3. Population inversion implies many photos are emitted per second