Quantum phenomena

Question 1

Describe the gold leaf electroscope parts

Answer 1

A metal plate attached to a right metal pole. Attached to this is a piece of gold foil.

Question 2

What causes the flexible gold foil to repel away from the metal pole?

Answer 2

Adding extra electrons
-This makes it negatively charged
-So both the pole and foil are negatively charged
-So it repels away

Question 3

What happens when light of a certain frequency is shone into the metal plate?

Answer 3

The gold foil falls back down

Question 4

Why does the gold foil fall back down when light of a certain frequency is shone on it?

Answer 4

-The light causes electrons to be released from the metal
-So apparatus becomes negatively charged
-So the repulsion weakens

Question 5

What happens if you charge the gold leaf electroscope experiment positively?

Answer 5

If the metal is positively charged then the negative electrons are attracted back to the plate so it’s harder for them to escape.

Question 6

What did wave theory predict about frequency?

Answer 6

Wave theory predicted that any frequency of light should cause the photoelectric effect

Question 7

How does frequency actually effect the photoelectric effect?

Answer 7

Only above a certain threshold frequency electrons are emitted

Question 8

What did wave theory predict about light intensity?

Answer 8

Wave theory predicted increasing light intensity would increase the energy of electrons emitted

Question 9

How does light intensity actually effect the photoelectric effect?

Answer 9

As long as you’re in the threshold frequency increasing intensity increases the amount of electrons. Energy stays the same.

Question 10

What does the existence of threshold frequency show?

Answer 10

Energy must be delivered in packets and must be proportional to the frequency of the wave.
All delivered in one go as electrons can’t store energy

Question 11

What is the photoelectric effect equation?

Answer 11

hf=ϕ+Ekmax

Question 12

How does a vacuum photocell work?

Answer 12

As you increase the voltage the eye becomes more negative and the smile becomes more positive
-So it’s harder for electrons to escape

Question 13

Vacuum photocell equation

Answer 13

eVs=Ekmax

Question 14

What happens if you heat up (excite) a gas?

Answer 14

You can cause it to glow.

Question 15

How can you heat up (excite) a gas?

Answer 15

You can heat them up by passing a very high current through them.
The high current is made of fast moving electrons.

Question 16

How do you see the multiple photons in a glowing gas?

Answer 16

Splitting light using a prism / diffraction grating

Question 17

What happens if you de excite (cool) a gas and pass white light through?

Answer 17

Certain photons are blocked

Question 18

Energy level rules

Answer 18

-Electrons can move up/down
-If they absorb energy they move up
-If they emit energy they move down
-Electrons cannot exist inbetween levels

Question 19

What is energy level 1

Answer 19

The ground state
Electrons are most stable here
Electrons have the least energy

Question 20

What is the ionisation level?

Answer 20

When electron has completely left the atom

Question 21

How can electrons gain energy?

Answer 21

Absorbing a photon or get hit by another electron

Question 22

What allows an electron to absorb a photon?

Answer 22

An electron can only absorb a photon of it gives it exactly the right amount of energy to move up 1 or more whole levels

Question 23

Ionisation energy

Answer 23

The minimum energy needed to remove an electron from the atom from the ground state

Question 24

Explain why an electroscope won’t show the photoelectric effect if it’s positively charged

Answer 24

Electrons would be attracted back by the positive charge
So the gold foil won’t stop repelling

Question 25

What is the threshold frequency evidence for?

Answer 25

Light can exist in discrete energy packets called photons As the electrons need all energy to be transferred at the same time to be emitted

Question 26

Explain why increasing the intensity of the light increases the amount of photoelectrons emitted?

Answer 26

Increasing the intensity increases the number of photons striking the plate per second. For each photon an electron is emitted. So the number of photoelectrons released per second increases.

Question 27

Define the work function of a metal

Answer 27

The minimum energy needed for an electron to be released from the surface of the metal

Question 28

Define the threshold frequency

Answer 28

The minimum frequency needed for an electron to be released from the surface

Question 29

When electrons are excited to a higher energy level explain why different frequencies are possible

Answer 29

Electrons cascade rather than going straight to the ground state

Question 30

Describe how the concept of energy levels is useful in the explanation of line spectra

Answer 30

Only certain energy changes allowed A line corresponds to a transition between levels Each transition corresponds to a definite wavelength

Question 31

What happens in an atom when line spectra are produced?

Answer 31

Electrons move up and down energy levels By emitting or absorbing a definite photon energy

Question 32

Explain what is meant by the duality of electrons

Answer 32

Electrons sometimes behave like particles and sometimes behave like waves

Question 33

Evidence that demonstrates electrons have particle properties

Answer 33

Deflection in E field

Question 34

State what is meant by the wave particle duality of electromagnetic radiation

Answer 34

EM radiation sometimes behaves like waves and sometimes behaves like particles

Question 35

Explain why the kinetic energy of emitted electrons has a maximum value

Answer 35

hf is energy received from photons Energy required to remove the electron varies So KE of electrons will vary

Question 36

Evidence for light behaving like particles

Answer 36

Photoelectric effect Existence of threshold frequency

Question 37

Evidence for light behaving like waves

Answer 37

Diffraction Interference pattern seen

Question 38

Evidence for electrons behaving like particles

Answer 38

Deflection in magnetic field Curved track of electron

Question 39

Evidence for electrons behaving like waves

Answer 39

Electron diffraction Interference pattern seen

Question 40

How does the wavelength relate to the diffraction gap

Answer 40

Same order of magnitude

Question 41

What does the mercury electron emit when it returns to ground state

Answer 41

Ultraviolet photon

Question 42

Why must a photon have an exact amount of energy whereas a free electron only needs a minimum amount of kinetic energy

Answer 42

For a transition an exact amount of energy is needed All of the photons energy is absorbed (1:1 interaction) Electrons can transfer part of their energy and have a lower speed

Question 43

How does the phosphorus coating work in fluorescent tubes?

Answer 43

-UV photons excite electrons in ground state of coating to higher energy level -Electrons cascade back down releasing lower energy photons

Question 44

How do fluorescent lamps work?

Answer 44

-High pd accelerates electrons across tube -These electrons collide with electrons in the ground state of the mercury -The mercury electrons gain energy and move to higher levels -When the move back down UV photons released -Phosphorous coating turns then into visible light photons