Module 4 - Quantum Physics

Question 1

What is the photoelectric effect? [6]

Answer 1

1. Removal of electrons from surface of a metal when exposed to light of a particular frequency/ wavelength.
2. Works with surface electrons.
3. A single photon interacts with a single electron.
4. Energy conserved in the interaction.
5. hf = {work function} +KEmax
6. Takes place when hf bigger than or equal to {work function}.

Question 2

Planck constant used in fundamentals of wave-particle duality and the essentials of wave-particle duality [6]

Answer 2

EM wave:

1. Behaves like an EM wave
2. E = hf

Moving electron:

3. Moving electron behaves like a wave
4. {wavelength} = h/mv
5. Wavelength of particle, m is mass of particle, v is speed
6. Electrons can be diffracted

Question 3

What is a photon?

Answer 3

One quantum of energy of electromagnetic radiation.

Question 4

What is one-to-one interaction?

Answer 4

A photon acts as a neutral particle and will either transfer all of none of its energy when interacting with one other particle.

Question 5

Define the electronvolt.

Answer 5

The kinetic energy gained by an electron when it is accelerated through a potential difference of one volt.

Question 6

Define threshold voltage of LEDs.

Answer 6

The voltage needed to give the electrons the same energy as a photon emitted by the LED.

Question 7

What conclusions can be made from the photoelectric effect?

Answer 7

1. For a given metal, no photoelectrons are emitted if the radiation has a frequency below the threshold frequency.
2. Photoelectrons are emitted with a variety of kinetic energies ranging from zero to a maximum value.
3. Number of photoelectrons emitted per second is directly proportional to intensity of radiation.