Quantum Oddnes

Question 0

What is wave particle duality?

Answer 0

An object displaying both wavelike and particle properties.

Question 1

Show that an electron can be a wave?

Answer 1

It can diffract.

Question 2

Show that an electron can be a particle.

Answer 2

It can collide with other electrons. If a current is passed through a gas the electrons of the electricity will collide with electrons of the atom, removing them and ionising the atom.

Question 3

Show that a photon can be a particle.

Answer 3

The photoelectric effect.

Question 4

Show that a photon can be a wave?

Answer 4

Is can diffract.

Question 10

What has the photoelectric effect have nothing to do with?

Answer 10

Energy levels.

Question 11

Explain the basics of the photoelectric effect.

Answer 11

A photon hits a de-localised electron in a piece of metal. The electron will absorb the energy of the photon meaning it is liberated. It can leave the metal.

Question 12

How does the photoelectric effect show that light can be a particle ?

Answer 12

If it was just a wave, then energy from different waves could build up in the metal meaning any wavelength of light would cause the effect. It will work or is won’t so the energy must come in photons or particles.

Question 13

What will one photon react with in the photoelectric effect?

Answer 13

One electron.

Question 14

How can the speed of a liberated photon be calculated?

Answer 14

Energy = 0.5mv²

Question 15

What does Ø mean?

Answer 15

The work function.

Question 16

Define the work function.

Answer 16

The minimum energy needed to liberate an electron from the surface of the metal.

Question 17

Define threshold frequency.

Answer 17

The minimum frequency with which a photon has sufficient energy to over come the work function and liberate an electron from the surface of the metal. Below this frequency nothing is emitted.

Question 18

Where is the work function shown on a graph?

Answer 18

It is the Y intercept

Question 19

Where is the threshold frequency shown on a graph?

Answer 19

The X intercept.

Question 20

What does the gradient on a photoelectric graph show?

Answer 20

The plank constant.

Question 21

What is the symbol of the threshold frequency ?

Answer 21

f”0”

Question 22

On a photoelectric graph, what is on the Y axis?

Answer 22

Maximum kinetic energy.

Question 23

On a photoelectric graph, what is on the X axis?

Answer 23

Frequency.

Question 24

What is the ground state ?

Answer 24

The energy level of an atom where the electron has the lowest possible energy.

Question 25

What is the photoelectric formula re-arranged to be a graph equation?

Answer 25

E"k" = hf-Ø
Y      = mx+c

Question 26

Why are electrons only emitted from a piece of metal when the light on it is of a certain frequency?

Answer 26

The energy of each photon of light will increase with the frequency.
The electrons of the metal need a minimum amount of energy to leave the metal. This energy is equal to the work function.
Thus the light frequency must be high enough so that the energy produced by a photon is enough to move an electron.

Question 27

Why is the particle theory of light better at explaining the photoelectric effect than a wave theory?

Answer 27

The energy of a photon increases with the frequency.
Electrons need a minimum amount of energy to leave the metal.
This amount of energy is equal to the work function.
This suggests electrons are given energy in one discrete event.
Thus light energy is concentrated (into photons)
Electrons don’t build up energy over time. Photoelectricity occurs immediately after light falls on it.

Question 28

Explain why when light is emitted on metal, why electrons are emitted and why the kinetic energy of the electrons varies up to a certain value.

Answer 28

Light is made of electrons whose energy depends on the frequency of the light.
Electrons on or near the surface of the metal can gain the energy of a photon when they meet.
Each electron needs a minimum amount of energy to leave and this is the work function.
This means the maximum kinetic energy of electrons emitted is the energy of a photon minus the work function.
Give reasons why electrons have different energies.

Question 29

What are electrons naturally inclined to do in terms to energy levels?

Answer 29

Go to the lowest energy level it can. It does this by emitting a photon.

Question 30

What happens if an electron comes into contact with a photon which will give to enough energy to not fit in any energy state?

Answer 30

An electron must absorb all of the energy or none of the energy. Thus if the energy of a photon won't put it in an energy level, it won't absorb it.

Question 31

What is the emission spectrum?

Answer 31

The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state

Question 32

Why are energy levels negative?

Answer 32

Because it is bound to the atom so you have to put energy into it to get it out. 0 is the largest energy level.

Question 33

What would happen if a -4ev electron absorbs a 7ev photon?

Answer 33

It will have ionised the atom, left and have 3ev

Question 34

What are the three main observations produced by doing experiments with the photoelectric effect?

Answer 34

No electrons are emitted if the light it below a certain frequency. The energy of the emitted electrons varies up to a maximum. This maximum depends on the frequency of the light. It is unaffected by the intensity. The number of photo electrons emitted is proportional to the intensity if the light.

Question 35

What would happen if white light was shown through some gas? | What would happen if that gas was heated up?

Answer 35

The light that came out if the gas would have a few absorption lines on it. When the gas was heated up, the few spectrums of light emitted would correspond to the gaps in the first one.

Question 36

When does diffraction occur?

Answer 36

When the particle interacts with an object with roughly the same de Broglie wavelength.

Question 37

What is meant by an excited atom?

Answer 37

An atom contains electrons that are at a higher energy level than the ground state.

Question 38

Describe the process where atoms in a fluorescent tube become excited.

Answer 38

A current is put through the tube, causing electrons to flow through it. These collide with atomic electrons raising the electrons to a higher level.

Question 39

What is the purpose of the coating on the inside of a fluorescent tube?

Answer 39

Photons emitted by the atoms will be of high energy. | The coating will absorb the photons which will then emit lower energy photos that in the visible spectrum.

Question 40

What must be done to validate the predictions of an unconfirmed scientific theory?

Answer 40

The Hypothesis is tested by experiments. These experiments are repeatable

Question 41

What is the ground state?

Answer 41

When the electron is in the lowest energy state. The most stable state. An atom is in the ground state when all of the electrons are in this state. It will be the largest negative number.

Question 42

In the photoelectric effect what does the reactivity of the metal have to do with it?

Answer 42

The more reactive, the easier it is to remove electrons and so the light can have a lower threshold frequency.

Question 43

Other than electrons, what else can excite an atom?

Answer 43

Other photons.

Question 44

Hydrogen has an ionisation energy of 13.6. What would happen if the atom interacted with a 13.6 ev photon?

Answer 44

The electron would be raised to the ionisation point but would fall back to the ground state emitting photons.

Question 45

What is an exited atom?

Answer 45

One where electrons have been raised to higher energy levels than the ground state.

Question 46

What is the threshold frequency dependent on?

Answer 46

The reactivity of the metal.

Question 47

If you draw a photoelectric effect graph, what goes on what axis?

Answer 47

Y axis, energy. X axis, frequency

Question 48

On the y axis of a photoelectric effect graph, what does a positive or negative value mean?

Answer 48

A positive value is the energy of the emitted electron. | A negative value is that of how much energy the electron is lacking.

Question 49

What is the work function of a metal from the photoelectric graph?

Answer 49

The negative of the y intercept.