Redshift, Doppler effect, Hubble law and the age of the universe

Section in Chapter 5 in the AQA AS Physics B textbook.

Covers Redshift, Doppler effect, Hubble law, and calculating the age of the universe in more detail than in the textbook.

I made this for peer teaching, useful for a better understanding of the definitions, understanding where the three topics link and where all those equations come from (which they don't explain in the book!?)