EM radiation + Quantum

Question 1

What is the photoelectric effect?

Answer 1

If we shine High enough frequency light onto a given metal we can liberate photoelectrons (electrons)

Question 2

Although you do not need to be able to recall the experiment, what were the 4 conclusions (PE EFFECT)

Answer 2

1) No electrons are emitted from the metal if the threshold frequency isn’t hit.
2) Emmited photoelectrons have varied Kinetic energy. (Higher frequency = Higher Ek) Due to E=hf
3) Number of electrons is directly proportional to intensity
4) The intensity does not affect the max KE of the electrons, it just means more electrons are liberated

Question 3

Why does the photoelectric effect suggest light is a particle not a wave?

Answer 3

If it was a wave, the continuous wavefront would eventually liberate electrons as it was exposed to the metal over a longer period of time. but it doesn’t.

Question 4

Photons have _________ with electrons

Answer 4

1 on 1 interactions

Question 5

What’s the ‘Work Function’?

Answer 5

The minimum amount of energy a photon must have to liberate an electron from a given metal

Question 6

How do we work out the max KE an electron can have?

Answer 6

Max Ke = Energy of photon - work function

Question 7

Increasing the frequency of the light would _________

Answer 7

Increase the max Ke of the liberated electrons

Question 8

What happens if we increase intensity of the light but not frequency?

Answer 8

More electrons are released but Ke stays the same.

Question 9

What is meant by ‘Discrete energy levels in atoms’?

Answer 9

Electrons can only exist with certain amounts of energy.

Question 10

What is the lowest energy level called?

Answer 10

The ground state. The lowest amount of energy an electron can have in a given atom.

Question 11

When electrons move up energy levels they are _____

Answer 11

Excited

Question 12

What happens when electrons drop down energy levels.

Answer 12

They give off photons with energy = to the distance.

Question 13

Define ionisation.

Answer 13

The removal of an electron from an atom.

Question 14

What’s ionisation energy?

Answer 14

Amount of energy to liberate an electron from an atom.

Question 15

How do fluorescent tubes work?

Answer 15

High voltage accelerates free electrons
These collide with mercury vapour electrons in the light
these collisions give off photons (as the mercury electrons de-excite)
these photons then collide with the phosphor coating of the bulb. as those electrons de-excite themselves, visible light is given off.

Question 16

What do line spectrums provide evidence for?

Answer 16

Electrons existing in discrete energy levels - it’s not a continuous spectrum.

Question 17

What is evidence for lights wave nature? Explain.

Answer 17

The diffraction of light through a grating. This can only be explained as a wave as if the particles were too big they’d just not go thru the gap and if they could fit they wouldn’t diffract as they do.

Question 18

what’s the evidence for light as a particle?

Answer 18

The photoelectric effect. The one-one interactions between light and the electrons in the metal seem to prove light is a particle.