Quantum Phenomena

Question 1

Give a brief explanation of what is meant by the Big Bang

Answer 1

The Big Bang is a model which says that at some time, roughly 13 Billion years ago, all the matter in the Universe was concentrated at a single point and was then blown apart in a massive explosion at the velocities we observe today.

The Big Bang theory explains the observed expansion of the Universe.

Question 2

Explain what is meant by the Cosmic Microwave Background.

Answer 2

• Background of low energy electromagnetic radiation observed to be coming form all directions of the Universe.
• The wavelength distribution agrees extremely well with the expected black-body radiation spectrum corresponding to the very low temperature of 2.73K.

Question 3

What is a black body?

Answer 3

It is a perfect absorber - one which absorbs all radiation incident on it, and hence appears black when light is shone on it.

Question 4

State the Heisenberg uncertainty principle and briefly describe its implications.

Answer 4

Δx Δp_x >= h/2

This influences the location of electrons in an atom and the lifetime of excited states

Question 5

What was it about neutrons that led to the discovery of quarks?

Answer 5

Neutrons have no net charge, but they do have magnetic moments. This is because they are made up of smaller components that do carry charge, the values of which cancel overall.

Question 6

What did Hubble’s observations tell us?

Answer 6

Distant galaxies appeared to be receding from us in all directions.

Question 7

What is the Cosmological principle?

Answer 7

• There is no particular reason to think that our galaxy is at the very centre of the universe
• if we lived in some other galaxy, every distant galaxy would still seem to be moving away. That is, at any given time, the universe looks more or less the same, no matter where in the universe we are.

Question 8

Potential Energy of galaxy… U =

Answer 8

U = - GmM /R

Question 9

Threshold frequency for photoelectric effect… f_{th =}

Answer 9

f_th = φ / h

Question 10

State the Pauli exclusion principle.

Answer 10

“No two electrons can occupy the same quantum-mechanical state in a given system”

Question 11

Wavelength and momentum… λ =

Answer 11

λ = h / p

Question 12

Energy of wave particle…. E =

Answer 12

E = hf

Question 13

Orbital magnitude L =

Answer 13

L = sqrt( l ( l + 1 )) h

Question 14

Compton Scattering λ_c =

Answer 14

λ_c = h/ mc

Question 15

Work function (eV)… φ =

Answer 15

φ = hf - E_k-max