Primary Survey Instrument

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APPENDIX 3

PRIMARY SURVEY INSTRUMENT

This Appendix contains a copy of the primary survey instrument which was administered to 231 first year physics students at the University of Sydney in 1995.

Presented in this Appendix are:

the Physics 1/1A Quantum Mechanics Concept Quiz questions,
the Answer Booklet, and
the “Official” Answers.

When the quiz was distributed to the students it appeared in two different formats. One of these is included here. The other format consisted of a simple renumbering of the items. Questions 1 and 2 were renumbered 3 and 4 and vice versa. This was done to promote an even distribution of responses.

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PHYSICS 1/1A :: QUANTUM PHYSICS

LECTURE 10 :: CONCEPT QUIZ :: 1995

QUESTION 1

Monochromatic light (light of a single colour) may be considered either as a continuous electromagnetic wave or as a stream of energy quanta (or photons). The photoelectric effect is the emission of electrons from a metal surface when light is shone onto the surface. The energy in the light is transferred to some of the electrons in the metal surface and they are ejected. Two key observations are as follows:

1. For monochromatic light of sufficiently high frequency, the rate of electrons ejected per second increases as the intensity of the light increases.

2. Electrons are ejected from the surface only when the frequency of the monochromatic light is above a certain frequency; and for monochromatic light below this frequency, no electrons are ejected no matter how great the intensity.

Picture in your mind the following model. Think of electrons in the metal surface as being like birds sitting on a telegraph wire. The effect of light could be pictured in two ways. If it is a classical electromagnetic wave then it would be like trying to dislodge the birds by shaking the wire. But the effect of the stream of photons (particles of light) would be like trying to knock the birds off the wire by throwing stones at them.

Wave Model / Particle Model

Which of these models can account for the above observations?

PLEASE ANSWER THE QUESTIONS IN THE QUIZ ANSWER BOOKLET.

QUESTION 2

In 1927 Werner Heisenberg published his Uncertainty Principle, which included the statement that all measurements have an associated uncertainty.

Consider a "measurement" involving catching a bus in a quantum mechanical world. Your timetable says that the bus will arrive at 9:00 am. Heisenberg would say that the time of arrival must have an associated uncertainty.

What does he mean by uncertainty?

Please answer the questions in the Quiz answer booklet.

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QUESTION 3

In classical physics we say that something is a particle if it has well defined position, velocity, mass, momentum and energy.

We also talk about another entity, a wave.

We know about water waves, surfing waves, radio waves, microwaves, sound waves and light waves. In 1924 Louis de Broglie proposed that electrons and other microscopic entities were also waves.

What do you mean when you say "something is a wave"?

Please answer the questions in the Quiz answer booklet.

QUESTION 4

You are listening to a discussion about the structure of atoms. You listen carefully to what Sue and Jim have to say and then they ask you for your opinion.

Sue:The lecturer said that the spectral lines observed in excited atoms is strong evidence that energy levels exist in atoms.

Jim:In 1913, Niels Bohr proposed a model for the hydrogen atom that combined the ideas of Max Planck's quantum theory, Albert Einstein's photoelectric effect and Ernest Rutherford's atomic model.

Sue:And... In 1924 Louis de Broglie proposed that electrons were also waves. The lecturer said that it was then proposed that the missing piece of Bohr's theory was that the electrons wavelength had to fit into the atom. Do you know what she meant Jim?

Jim: No. But I think it had something to do with the energy levels.

{ Sue and Jim turn to you and Sue asks }

Sue : I don't understand what she meant by energy levels and I don't understand what she meant by the wavelength of an electron fitting into the atom. Do you know?

You have been asked to join into the conversation.

Think carefully about the points Sue and Jim have been discussing, and

WRITE YOUR RESPONSES TO SUE'S QUESTIONS

IN THE QUIZ ANSWER BOOKLET.

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PHYSICS I :: QUANTUM PHYSICS
Physical / Technological - 1995

Concept Quiz

Answer Booklet

Student ID : ______

PLEASE NOTE : This quiz is intended only for diagnostic purposes.
It will NOT be used for any kind of assessment.
We require your Student ID so that we may invite
sample groups to participate in further research projects.
This Quiz Answer Booklet cover sheet will be separated
and your Student ID encoded to ensure your privacy.

QUESTION 1 - PHOTOELECTRIC EFFECT

Part A)

Consider the first key observation, that for monochromatic light of sufficiently high frequency the number of electrons (birds) ejected per second increases as the intensity of the light increases.

Please tick ONE of the following boxes

This key observation can be explained by

the wave model but not the particle model.

the particle model but not the wave model.

both the wave and particle model.

neither the wave nor the particle model.

In terms of the "bird on a wire" picture explain your answer in your own words and/or diagrams.

______

Part B)

Consider the second key observation, that electrons are only ejected from a metal surface for frequencies of light above a certain frequency (eg. violet and ultraviolet) and not for frequencies below (e.g. blue, yellow or red light).

Please tick ONE of the following boxes

This key observation can be explained by

the wave model but not the particle model.

the particle model but not the wave model.

both the wave and particle model.

neither the wave nor the particle model.

In terms of the "bird on a wire" picture explain your answer in your own words and/or diagrams.

______

IF THERE IS INSUFFICIENT SPACE FOR YOUR ANSWER
PLEASE WRITE ON THE OTHER SIDE OF THIS PAGE

QUESTION 1 - PHOTOELECTRIC EFFECT

ADDITIONAL SPACE

Part A)

______

Part B)

______

QUESTION 2 - CATCHING THE QUANTUM MECHANICAL BUS

Catching the quantum mechanical bus.

Please tick ONE of the following boxes

Consider the meaning of the word uncertainty in relation to a quantum mechanical system. Which of the following statementsdescribes most clearly what the word "uncertainty" means in this context.

If you caught the same bus every day for one year, its arrival time would vary even though on average it would arrive at 9:00 am.

You could never be sure exactly when the bus would arrive because it may not have left on time or may have been delayed in its journey.

Quantum mechanics says you can not predict results of an experiment, so there can be no such thing as a time-table for a quantum mechanical bus.

Even if the bus arrived perfectly on time at 9:00 am you could never be sure it was on time because no watch is ABSOLUTELY accurate.

None of the above statements.

In your own words and/or diagrams support and explain your answer.

______

IF THERE IS INSUFFICIENT SPACE FOR YOUR ANSWER
PLEASE WRITE ON THE OTHER SIDE OF THIS PAGE

QUESTION 2 - CATCHING THE QUANTUM MECHANICAL BUS

ADDITIONAL SPACE

______

QUESTION 3 - SOMETHING IS A WAVE

Please tick ONE of the following boxes, which states most clearlywhat you mean when you say "something is a wave".

A wave is an entity that is not a particle.

A wave is an entity that does not show well defined position, velocity, mass, momentum and energy.

Everything is a wave and what we call a particle is only a special localised wave called a wave packet.

None of the above.

In your own words and/or diagrams support and explain your answer.

______

IF THERE IS INSUFFICIENT SPACE FOR YOUR ANSWER
PLEASE WRITE ON THE OTHER SIDE OF THIS PAGE

QUESTION 3 - SOMETHING IS A WAVE

ADDITIONAL SPACE

______

QUESTION 4 - STRUCTURE OF THE ATOM

Sue's and Jim's discussion about the structure of the atom.

Part A)

In your own words and/or diagrams explain what the lecturer meant by the

term "energy levels".

______

Part B)

In your own words and/or diagrams explain what the lecturer meant when she said

that the electron's wavelength had to "fit into the atom".

______

IF THERE IS INSUFFICIENT SPACE FOR YOUR ANSWER
PLEASE WRITE ON THE OTHER SIDE OF THIS PAGE

QUESTION 4 - STRUCTURE OF THE ATOM

ADDITIONAL SPACE

Part A)

______

Part B)

______

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OFFICIAL ANSWERS

PHYSICS 1 - QUANTUM PHYSICS - CONCEPT QUIZ - 1995

SOMETHING IS A WAVE

"None of the above" would be the most appropriate response.

A wave is a phenomenon by which a disturbance (energy) propagates through a medium, without long-term change to the medium, and which exhibits properties commonly associated with other things we call 'waves'.

it is usually non-localised

it can be described mathematically and would obey a 'wave equation'

when it is initiated by a periodic disturbance it will have wavelength, frequency and amplitude

as it moves it exhibits reflection, refraction and absorption

MOST IMPORTANTLY (in the context of quantum physics) it obeys the principle of superposition - it exhibits diffraction and interference

STRUCTURE OF THE ATOM

Part A - Energy Level

For any system made up of 'bits' there should be in principle lots of ways to put it together and these constructions would be characterised by different energies. For example, a planet in a solar system could exist at any distance from the sun, therefore there are an infinite number of ways of constructing such a solar system. Whereas in an atomic system we know that only some internal structures (energies) are allowed in nature, these are called Energy Levels.

Part B - Electrons wavelength having to fit into the atom

If an electron is behaving like a wave inside an unchanging energy level then the electron must be a standing wave. The characteristic of a standing wave, like for a violin string or a column of air, is that the wavelength must 'fit into' the length of the string or pipe. Therefore the circumference of the electron's orbit must be a whole number of wavelengths.

CATCHING THE QUANTUM MECHANICAL BUS

Uncertainty in this context means "If you caught the same bus every day for one year, its arrival time would vary even though on average it would arrive at 9:00 am".

The idea of uncertainty was proposed in response to the wave particle duality of microscopic objects. Knowing where an object (the bus) will be at a particular time is a particle-like measurement. But nature tells us that quantum mechanical objects do not necessarily behave like particles. This means if you travelled back in time and repeated your measurement of the object's position at the same time you would not necessarily get the same answer. The results of such a measurement must be uncertain.

Note that uncertainty has nothing to do with the inaccuracy of your measuring instruments or lack of knowledge of what happened to the object earlier.

PHOTOELECTRIC EFFECT

Firstly it is important that we understand what the terms frequency and intensity mean in the context of the wave and particle models.

In the wave model

frequency corresponds to how often the wire is shaken

intensity corresponds to the amplitude of the shaking motion

In the particle model

frequency corresponds to the energy of the projectiles being thrown at the bird by the relation E = hf (Energy = Planks Constant x Frequency)

intensity corresponds to the number of projectiles per second being thrown at the bird

Part A - First key observation

"both the wave and particle models"

Consider the first key observation, that for monochromatic light of sufficiently high frequency the number of electrons (birds) ejected per second increases as the intensity of the light increases.

The wave model says for birds on the wire

Increasing the intensity corresponds to shaking the wire with an increased amplitude.

If you increase the amplitude, a bird is more likely to be dislodged from the wire.

The particle model says for birds on the wire

Increasing the intensity corresponds to throwing more projectiles at the bird.

If you throw more projectiles a bird is more likely to be hit and knocked off the wire.

Both models predict the experimental observations.

Part B - Second key observation

"the particle model and not the wave model"

Consider the second key observation, that electrons are only ejected from a metal surface for frequencies of light above a certain frequency (e.g. violet and ultraviolet); and for light below this frequency (e.g. blue, yellow or red light) no electrons are ejected no matter how great the intensity.

The wave model says

If you shake the wire at very low frequencies you will never dislodge the bird no matter how great the amplitude (intensity).

This is nonsense, if you shake the wire with a low frequency of once per second but increase the amplitude to 10,000 kilometres I bet the bird comes off the wire.

Therefore the wave model fails to explain the observation.

The particle model says

If you throw low energy projectiles (corresponding to a low frequency) then no matter how many you throw the bird will be able to hang on.

But if the projectile has a higher energy (corresponding to a higher frequency) then one direct hit will knock the bird off the wire.

Thus only the particle model correctly predicts the experimental observations.

APPENDIX 3...... 105

PRIMARY SURVEY INSTRUMENT...... 105