13 - Quantum Physics

Question 1

What are photos?

Answer 1

Photos are particles of light.

They are sometimes referred to as a quantum of energy of EM radiation. “A quantum” in this context just means a set finite amount

Question 2

The energy of a photon is proportional to what?

Answer 2

The frequency

Question 3

The energy of a photo is inversely proportional to what?

Answer 3

The wavelength

Question 4

What is h in this equation E = hf?

Answer 4

h is the Planck constant, measured in Js

Question 5

What quantity can be measured in electronvolts eV?

Answer 5

Energy

Question 6

What is the photoelectric effect?

Answer 6

The photoelectric effect is a phenomenon where shining light with enough energy onto a metal releases electrons (and can cause a current to flow)

These electrons are called photoelectrons

Question 7

What features of the photoelectric effect can’t be explained if light is a wave?

Answer 7

If light was a wave, then the energy of the electrons released would increase with increasing intensity of the light - but this isn’t the case. Instead the energy of the electrons depends on frequency (and no electrons are released below a certain threshold value, no matter the intensity)

Question 8

How many photons does each photoelectron absorb prior to emission?

Answer 8

1

Question 9

How does the photo model of light explain the threshold frequency seen in the photoelectric effect?

Answer 9

Each electron absorbs a single photon. This single photon must have enough energy for the electron to be released. If it doesn’t the energy is re-emitted. The electron can’t build up energy as it could if light was a wave.

Question 10

What is the name given to the minimum amount of energy an electron required to leave the surface of a metal?

Answer 10

The work function (or work function energy)

Question 11

Word equation relating the energy of an incident photon to the work function and the kinetic energy of released electrons

Answer 11

Photon energy = work function + kinetic energy

Question 12

The rate of emission of photoelectrons is proportional to what?

Answer 12

Intensity

Question 13

Does the maximum kinetic energy of a released electron depend on the intensity of light hitting the surface?

Answer 13

No.

Energy transferred is due to a one-to-one interaction, and so depends on frequency, not intensity