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Flashcards in 13 - Quantum Physics Deck (24)
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1
Q

What is a photon?

A

A tiny packet of electromagnetic energy.

2
Q

What is the energy of a photon directly proportional to?

A

The frequency of a the photon.

3
Q

What is the Planck constant?

A

6.63x10^-34 Js

4
Q

Why is it impractical to measure the energy of photons in joules?

A

Because they are so small,

5
Q

What unit do we use to measure the energy of photons?

A

The electronvolt (ev)

6
Q

Define the electronvolt.

A

The energy transferred when an electron moves through a potential difference of 1v.

7
Q

What do we multiply ev by to convert to joules?

A

The charge of an electron.

1.6x10^-19

8
Q

What is the photoelectric effect?

A

When high energy electromagnetic radiation shines on a metal, it causes electrons to be emitted from the surface of the metal.

9
Q

What are emitted electrons called?

A

Photoelectrons

10
Q

What is the threshold frequency?

A

The lowest frequency of electromagnetic radiation that will cause a certain metal to emit photo electrons.

11
Q

What is the threshold frequency unique to?

A

The metal.

12
Q

How does increasing the intensity of the light affect the photoelectric effect?

A

It increases the number of photoelectrons emitted but not their energy.

13
Q

How does increasing the frequency of the light affect the photoelectric effect?

A

It increases the energy of the photoelectrons but not the number that is released.

14
Q

What is the work function of a metal?

A

The minimum energy required to free an electron from the surface of a metal.

15
Q

How do photons interact with electrons in the metal?

A

In a one to one interaction.

16
Q

What does the kinetic energy of the photoelectron depend on?

A

How much energy is remaining once work has been done to overcome the work function.

17
Q

How fast is emission if the frequency of the light is over the threshold frequency?

A

Instantaneous.

18
Q

What happens when a photon hits a metal?

A

Its energy is transferred to the electron in a one to one interaction. If this energy is greater than the work function, the electron is emitted from the metal. Any left over energy is converted to kinetic energy.

19
Q

What will happen if the light hitting the metal is at the threshold frequency?

A

The electrons will be free from the surface of the metal however they will have no kinetic energy and so they will not move anywhere.

20
Q

What is Einstein’s photo electric effect equation?

A

Energy of a photon = work function + maximum KE

21
Q

Why does Einstein’s equation use maximum kinetic energy?

A

Because the work function is the lowest amount of energy required to free an electron.

In reality, it could be more as the force that has to be overcome depends on the relative positions to the protons.

22
Q

How can we prove that electrons can behave as a wave?

A

They diffract when fired through graphite.

spacing between atoms in graphite is equal to wavelength of electrons

23
Q

What does wave-particle duality mean?

A

Something behaves both as a wave and as a particle.

e.g. Light - reflection = wave / photoelectric effect = particle

24
Q

What does an electron diffraction pattern look like?

A

Rings