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PROTONS FOR
BREAKFAST
SPRING 2013
WEEK 2
LIGHT
1
This is what you said on the feedback forms in Week 1
You said…
Michael said..
 You have obviously  I do indeed have a vast library of songs and recently
got a vast and
they have become available on iTunes. Details here:
fantastic library
http://protonsforbreakfast.wordpress.com/songs/
of science songs.
but don’t look if you want the songs to be a surprise
Please could you
each week .
provide links to
 Somewhere else in these notes I described how in
them.
magnetic materials the electrons orbiting around one
 Why are there
atom orbit in the same sense as their neighbouring
only 3 magnetic
atoms. So lots of electrons all orbit neighbouring
elements? What
atoms in exactly the same way. The conditions that
makes them
allow this kind of ordering are quite rare so magnetic
magnetic? Will you
behaviour is not very common. Iron, Cobalt and Nickel
be explaining
are strongly magnetic at room temperature, but in
magnetism again?
Week 3 we will see how temperature affects
 Are the fields
magnetism.
made up of
 No, fields are not made up out of particles of ‘stuff’.
electrons?
We will look at this again this week. And demonstrate
the nature of fields with Jelly babies.
 It is fascinating learning
 Fascinating and shocking. It is difficult to
about the power of ten and
feel comfortable in a Universe that is quite
that is a mere speck in the
so disturbingly large.
universe.
 I don’t think so, because I have never come
 Is the universe infinite?
across anything in physics which is infinite. I
 It is a quantum fluctuation!
think infinity is just a concept in
(I think that is sciency
mathematics.
language for nobody knows.)  Didn’t I say that? It sounds familiar! But I
I learnt loads and this only
am glad you learned a lot.
the first session! But what
 I am afraid protons don’t eat but they must
protons do we eat for
be hungry! They were all formed between 3
breakfast?
minutes and 20 minutes after the big bang –
 And what is your favourite
and they haven’t had a meal since!
periodic element?
 My favourite element? Tricky. I think it is
 Loved the talk and can’t
probably potassium which I studied in great
wait till next week!.
detail for my PhD. More recently I have
studied argon a lot but we haven’t really
grown to be friends.
 It’s here already!
2
You said…
Michael said..
We already knew about the experiments
It is difficult to get the balance
or had been shown them before hearing
right for everyone. The idea of
your lecture, so probably it would be
having things available beforehand
more interesting if we got to observe
and at the break is that the meaning
other experiments (on that same concept of what you see may have changed.
of course) or they were not displayed
We try to keep things simple and
before your lecture.
social. In the break you can talk to
The delivery style is very lucid and
other people, or helpers. Or me! I
entertaining and attempts to kindle
think it is very important to link
interest and keep one listening in a
together theoretical ideas and very
positive way, so great job Michael, keep
mundane experiments and understand
on going!!
the relationship between them
Glad you like the style – I have no
choice about it!
How were
Simple question complicated answer. I think it was the
atoms
culmination of a large number of observations many of which you
discovered
can make for yourself. Here are some:
within
 Leave out a saucer of water in your home and the water will
everyday
disappear! (We say it has evaporated)
objects?
 If you chill the now empty saucer, then water will reappear
on its surface (We say it has condensed).
 If you cool water further it changes from being able to flow
to forming a rigid shape. And then on warming it regains the
ability to flow. (We say it was frozen and melted).
 Thinking about all these common properties of water – what
could possibly be its microscopic structure?
However going from this kind of insight to a theory with
different types of atoms took hundreds of years. It is not at all
obvious.
Great introduction to
Thanks. More adventurous? What an interesting
the nature and expanse comment. Do you mean I could have added more detail?
of science. Could have
Well it’s a difficult choice. I can add more detail at the
been a little more
expense of a song. Or at the expense of repeating
adventurous with the
something. Or a demonstration. Intellectually I think
explanations.
the course is really quite ambitious. And it is intended
to be for everybody. See how you feel after this
evening’s session!
3
You said…
1. Why, if string
theory is
hypothetical, does it
not become proven
conclusively by the
discovery of the
Higgs Boson, which
majorly proves the
Standard Model, and
thus most aspects of
Type II superstrings?
2. Electricity would
be strictly classed as
electromagnetism, so
what are the core
concepts of the initial
equations of Grand
Unified (Theories) –
for example, in the
relativistic massenergy equivalence
formula, energy =
mass times the speed
of light squared, so
how do the GUT
equations equate
these variables.
3. Could you please
explain the de Broglie
hypothesis?
Michael said..
1. As understand it, string theory has no predictions
about any of the discovered particles. It is describing
physics on a much grander scale and all of the physical
reality we observe – protons, electrons, atoms etc. – is
just a detail. The Higgs boson is indeed a feature of the
Standard Model but the standard model has nothing to
do with string theory. Many scientists consider string
theory is not just hypothetical, but that it is so
detached from reality that it can never be demonstrated
to be either wrong or right. Time will tell.
2. As I mentioned, we now understand magnetism is not
separate from the electric field, but is just how the
electric field looks to us when charged particles are in
motion. So electromagnetism is a ‘unified’ theory – one
theory explaining two categories of phenomena – electric
and magnetic. Similarly we used to think that there were
two distinct kinds of nuclear force called the weak
nuclear force and the strong nuclear force. However now
we understand that the electric force and the weak
nuclear force are simply different aspects of one force
which we call the electro-weak force. Many scientists
believe that there must be a connection between all the
forces we observe electro-weak, strong nuclear, and
gravitational. Such a theory is called a grand unified
theory (GUT) . However although people have tried to
construct such a theory, none have been successful.
3. In the 1920’s Davidson and Germer in the USA
demonstrated that electrons could be diffracted and so
behave like a wave. Louis de Broglie (a PhD student!)
tried to understand how electrons could sometimes
behave as a particle and sometimes as a wave. He
hypothesised that the particle is accompanied by some
kind of a ‘pilot wave’ that guides the particle where to
go. He imagined that this pilot wave could be diffracted,
and then guide the particle to an unexpected position. He
then calculated the wavelength of the ‘pilot wave’ in
terms of the momentum of the particle. This particular
theory isn’t widely held now, but gave rise to
Schrödinger’s Wave Equation which essentially replaces
Newton’s Laws when talking about the laws of motion of
small particles.
4
You said…
 What
happens if
you split
atomic
particles?





Is light a
wave or a
particle or
both?


Michael said..
It depends what you mean by ‘atomic particles’. Splitting
atoms is common – we took electrons off atoms using the
balloon and so made ions.
But what people normally mean by ‘splitting atoms’ is
splitting the nucleus of an atom. Suppose we have a heavy
nucleus such as that of uranium. A uranium nucleus has 92
protons and typically ~146 neutrons. If it is split by
disturbing it in some way – such as firing a neutron into it,
the nucleus will split into (typically) two large chunks and
several smaller chunks.
Each piece of debris containing protons will form the
nucleus of a new atom – and the number of protons in each
piece of debris determines the type of atom i.e. which
element is formed.
Suppose a nucleus split into three chunks with 40, 45 and 7
protons respectively. These would form nuclei of zirconium
(Zr), Rhodium (Rh) and nitrogen (N). Each nucleus would
gather around the matching number of electrons to make
the atom neutral. Each nuclear chunk would have a slightly
random number of neutrons because of the chaotic nature
of nuclear split. This will make the nuclei unstable – and
bits of nuclei will then be ejected in a process known as
radioactive decay – more in Week 6.
The fundamental nature of light is whatever it is, but we
notice that:
o Light is emitted by single atoms in a single place
o Light travels through space as a wave
o Light is absorbed by single atoms in a single place
Technically we can describe this as the creation of a
particle (called a photon) and its subsequent annihilation.
Personally I think that although it is technically correct, at
the level we are discussing the world the description is
misleading. Most people think of ‘a particle’ as a ‘thing’ or as
‘stuff’. But a photon comes into existence when an atom
vibrates, and then pops out of existence when it makes
another atom vibrate. That doesn’t sound very particle-like
to me. I think in almost all cases the classical description
of light is closer to reality. To answer your question, light
is light, and sometimes it behaves a bit like a particle, but
mostly it behaves like a wave.
5
You said…
Michael said..
Interactive. Interesting.
Mmmm. Is that an instruction to “Make Science
Mind blowing. Make science Easier to Understand !” or a statement that that
easier to understand.
is what I am doing? Either way I will do my best!
Really enjoying the storylines. I teach
Really glad you are enjoying the
science (physics) and it’s fascinating to
course and that you are tuning in to
hear how well the story connects when
the story. The basic story of physics
there’s a bit more stretch included. Very is very simple and very compelling.
enjoyable – can’t wait until my 2 boys are And every time I re-tell it, it is like
old enough to come.
discovering it again.
If there are loads of
 Since people developed telescopes capable of
galaxies then how do we
spotting planets orbiting other stars they have
know that there is not other
discovered hundreds of planets and it is clear
intelligent life-forms? And
that planets of all types – large and small, hot
do you think that there are
and cold, wet and dry – are common throughout
other intelligent life-forms?
the Universe. Given such a wide range of
Is it possible that there may
planets I think most scientists would expect
be life-forms on planets like
life in some form to exist on some of these
Mars and the moon and the
planets.
other planets in our solar
 Even on Earth we find it hard to categorise
system and universe that
exactly what is living and what is not. So for
don’t breath oxygen or
example, viruses are considered to be on the
survive on liquid water and
border of the inanimate. Life on other planets
glucose? and I’m not asking
could be (and no joke intended) completely
about bacteria.
alien, and we may not even recognise it. It
Shouldn’t Protons for
might respond to its environment much slower
Breakfast be called Protons
than we expect and so appear inanimate to us.
for Dinner (because it’s
 Well I have thought about the name and I
dinner time (7:00)). Great
thought the words ‘protons’ and ‘breakfast’
job, really interesting. Love
went well together. I think it is because
the tea.
breakfast is perhaps the most personal meal of
the day.
 Glad you are enjoying it.
Very interesting. Changed my outlook on “stuff”.
Excellent!
6
You said…
Very mind
boggling
things! How
do
scientists
make
microscopes
see so far?
Michael said..
It is indeed mind boggling. One of the great ‘tricks’ that scientists
use is this: They write down what they did and publish it in
scientific ‘journals’. This saves people from having to spend a long
time re-discovering stuff. So that if one person builds a
microscope or telescope one way and describes what they have
done, someone can read it and then maybe try a different
technique. So modern telescopes and microscopes in all varieties
are built on hundreds of small insights and tricks along with the
occasional stroke of genius. Think about a modern car – it is
enormously better than the cars built in the 1960s, but those
improvements came gradually even though many were obvious. Cars
are now faster, cheaper, lighter, quieter, and more fuel efficient.
It is the same with scientific instruments. BY reading about what
other people have done we can make progress without having to
waste years following a dead end.
What is gravity?
Gravity is a force which we observe between any objects
You said you didn’t
with the property of mass. Newton calculated the
know why it works.
properties of gravity and realised that exactly the same
But great talk. Even force which pulled an apple to Earth, also made the Moon
I got most of it, and orbit the Earth. An amazing insight.
I was only here for
After 300 years of thinking that Newton’s vision was the
my grandson.
last word on the matter, Einstein then noticed further
incredibly obvious things about gravity, and developed his
breath-taking general theory of relativity. It is Einstein’s
modern theory that I don’t understand.
I hope you and your grandson enjoyed yourselves.
Thanks for sharing the fun
I am glad in my heart that you enjoyed it: 
with us! I loved it.
Paper is full of
Ha Ha! No. To me the greater miracle is that most things
atoms, is that why
don’t get lost in the post – but then I am not the best
letters get lost in
organised person in the world.
the post? Why does The aluminium stuff was a thin layer of Mylar plastic
a balloon gradually
coated in aluminium. On the balloon or the Mylar shape
slide off the wall,
there is a concentration of electrons which are repelling
when that very fine each other, but they can’t move because they trapped on
aluminium stuff
an insulator, and the wall is an insulator too. But nothing is
does not?
a perfect insulator – and eventually the charges repel each
other and the electrical attraction to the wall is reduced.
Balloons weigh around 10 grams but the Mylar shape
probably weighs less than 0.1 g. So it takes much less
charge to hold up a piece of Mylar than it does a balloon. I
think the Mylar shape will fall to Earth eventually.
7
You said…
Is a light year is
the time that
takes light to
travel in 1 year?
The distance
that 1 light year
is calculated to
be 1016 (more or
less)?
How long would
it take us to
travel to that
point where light
originates from.
Would we ever
reach that point
of origin.
Michael said..
Ahhh. A light year is not a time, but a distance. Light travels
through a vacuum (or air) at around 3×108 metres per second.
i.e. 300,000,000 metres per second.
So:
 in 1 second light travels 300,000 kilometres
 in 1 minute light travels 60×300,000 kilometres =
18,000,000 kilometres (18 million kilometres)
o This distance is a light minute
 in 1 hour light travels 60×18,000,000 kilometres =
1,080,000,000 kilometres. Or 1.08 ×109 km. Just over a
billion kilometres.
o This distance is a light hour
 in 1 day light travels 24×1.08 ×109 km = 25.92 ×109 km.
Nearly 26 billion kilometres.
o This distance is a light day
 in 365.25 days light travels 365.25×25.92 ×109 km =
9.5 ×1012 km.
o This distance is a light year
To find the time to travel to the point where light originates
you take the distance, and divide by the speed of light. So for
the light bulb in your room which is 3 metres away, then the
time taken is
3 metres divided by 300,000,000 metres per second
Which is 10-8 of a second, or 10 nanoseconds. During this time
your computer with a CPU operating at 2 GHz could do 20
calculations.
What is an
I don’t know. I have never heard of an electrostring
electrostring force?
force. Sorry. Or was that electro-strong? We don’t know
Is there a weak
of any connection between the strong force and
force? So many
electricity.
questions! This is
Yes there is a force called the weak nuclear force. It’s a
very relevant to my
bit complicated to describe here, but we now know that it
physics and
is related to the electric force.
chemistry GCSE.
I am glad you are able to make the connections to your
GCSE 
It was fun, interesting, and I learnt a lot.
I am glad 
Fun, lively and very interesting. Great. I am looking forward to it too.
I look forward to next week.
8
You said…
Question: When the big
bang happened there was
a massive outward force
that is meant to still
slowly be happening. If
so in a certain period of
time will this force the
earth apart into the
original chunks that
collided together to
create the big bang
theory.
Feedback: Personally
enjoyed very much the
way you gave the
information because it
kept me interested and
made me really question
what I know, which really
helped me remember all
the things you said and
all the things I learnt.
The demonstrations you
gave I have seen before
but I felt that the way
you showed and
explained them helped
me understand and enjoy
seeing it again.
Michael said..
Answer I don’t think so. There are three aspects to
the way the universe grew (and is still growing) after
the big bang
 In stage 1 the Universe is thought to have
undergone ‘inflation’. This very short phase began
roughly 10-36 seconds after the big bang and lasted
until roughly 10-32 seconds i.e. it lasted for roughly:
0.000 000 000 000 000 000 000 000 000 000 1
seconds
During this time, the Universe is thought to have
grown by a factor roughly 1030 in size for reasons
that nobody can explain. After this ‘inflationary’
era the universe grew for two reasons.
 One was the explosive momentum we can all
imagine from any explosion. This force won’t tear
the Earth apart because the explosion is pretty
quiet now – it has been 13.5 billion years or roughly
4.3 ×1017 seconds since the big bang.
 The other expansion was the expansion of the
space in which cosmologists imagine the matter of
the Universe resides. So although it is only 13.5
billion years since the big bang and matter cannot
travel faster than light, cosmologists estimate the
universe is around 78 billion light years in
diameter. The difference is due to the expansion
of space. This expansion too is rather tame now
and will not tear apart the Earth.
Glad you enjoyed the demonstrations. I still enjoy
each of the demonstrations no matter how many times
I have seen them before.
Mind boggling.
Indeed – but I hope you were able to cope?
Fantastic enthusiasm from Michael. Glad you enjoyed it. The second half was a
Coffee break could be short (say
bit a rushed: sorry – it isn’t normally, but I
15 mins), and last ½ hour felt
am not sure why it was this week. In Week
rushed (so much fascinating stuff
1 the break is relaxing but we have more
to take in).
for you do next week!
Had a really great time, it was pitched at the perfect
Glad you enjoyed it.
level for everyone, and not too much info at once.
9
You said…
Why do you get
random electric
shocks?
Do you get
headaches as a
result of
atoms/electrons
etc. in the
atmosphere?
Why did people
think
electrotherapy
would help
people with
mental
problems?
Explain the
science behind
it.
Michael said..
I think you are talking about the electric shocks one often
gets in offices or sometimes on exiting motor cars. The
processes that cause these shocks are complicated but the
main culprits are electrical insulators.
 In the natural world, very few materials are good insulators.
Amber is one of the few and that is why everything to do
with electricity is named after the Greek word for amber elektron.
 The rubbing that I used to charge the balloon is a very
common process – every time you walk or your clothes rub
against something, charging takes place.
 With natural materials, the charges can find imperfections
in materials that allow them to move away from each other,
and so with natural materials we tend not to get such strong
charging effects.
 The modern materials that we use in our clothes and in
carpets and constructional materials are made of plastics
which can be fantastic insulators. When we place charges on
their surface, by walking or rubbing, the charges can’t
escape. So walking on a carpet we can lose electrons and
then a few seconds later when we touch something we get a
shock as some electrons in the door handle (they get
everywhere!) jump the gap and stimulate our nervous
system, which is also electrical.
I don’t suffer much from headaches, aside from the wellunderstood effect of carbon, oxygen and hydrogen atoms
arranged to make C2H5OH - ethanol.
I can’t explain the science behind electrotherapy – electric
shock therapy – because I don’t think there is much. The
widespread use of electric shock therapy – in which large
electric currents were passed through people’s brains as
treatment for mental disorder – seems like a shameful episode
in the history of medical science.
10
You said…
Comment: Very
good lecture.
Question: I
know you didn’t
want to get into
it, but does
electrical
charge create
permanent
magnetism in
metal (iron)?
Michael said..
Glad you enjoyed it
 Permanent magnets are complicated. We will say a little bit
more about them in Week 3.
 The magnetism in materials like iron arises
from two sources, one of which is well
understood, the other not so much. As I
mentioned electrons ‘orbit’ atoms and so
motion of the electron in some orbits is
like a tiny loop of electric current. The
motion of the electron has no effect on
stationary charges, but we describe its
effect on other moving charges as a
‘magnetic’ effect.
 Thus in some atoms each orbiting electron behaves like a
tiny atomic-size version of a bar magnet.
 In a few materials the electrons naturally arrange their
orbits so that electrons orbiting on neighbouring atoms all
go around in some sense. Why? Because it minimises
electrical repulsion between electrons on neighbouring
atoms. But this means that the magnetic effects of lots of
atoms add up – like lots of tiny bar magnets lining up. The
force causing the alignment is straight-forward electrical
repulsion.
 As you may know when you try to line up bar magnets the
same way around – they tend to try and flip the other way.
In a normal piece of iron, the atoms are nearly all aligned
with their neighbours, but the direction of alignment
changes from one region to another. Typically the volumes
where the atoms are aligned (called domains) are around
0.001 mm in size.
 Making a permanent magnet out of iron involves a number of
tricks for getting the domains to align (such as applying a
big magnetic field) and then stay aligned when the aligning
field is removed (such as damaging the crystal structure by
beating it!)
Like I said: it’s really complicated.
11
You said…
Michael said..
A question: Is
Mmmm. Very interesting question but I am not quite sure what
there any way
you are getting at. I can think of two possibilities depending on
to measure the whether you had in mind gravitational fields or electric fields.
ratio of mass
The gravitational force on an object depends on the object’s
and fields in an
mass. So the ratio of mass and gravitational force will just be a
area? Is there
constant that tells us the strength of the gravitational field.
any variations
Or alternatively, according to Newton’s second law, the
at all?
acceleration of the object.
A comment:
Or are you asking whether the electric field affects the mass
Best lecture
of an object? I have never come across anything to suggest
ever seen as it
that might be true. If I have got hold of the wrong end of the
was both
stick please ask me again!
educational and Glad you enjoyed it. I am blushing 
funny.
A completion of my knowledge
A completion?! No, more like a taster! You could
of electricity and magnetism.
spend your entire life studying this and still find
phenomena that would surprise you!
What is ‘dark
‘Dark Matter’ is matter that astronomers believe exists all
matter’?
around us but which we cannot see or detect except by its
Absolutely
gravitational effect – except in our laboratories we can’t even
fascinating
detect that!! Why do astronomers believe it exists? Because
presentation.
when they look at stars in distant galaxies, they see that they
Captivating.
are bound into the galaxy with a gravitational force which is
Many thanks!
too strong to be accounted for by the matter they can see.
Now you or I might say “Mmm, that’s curious, there is
something we don’t quite understand about galaxies”, but
astronomers are bolder than you or I. They say “We
understand everything about distant galaxies therefore there
must be some “Dark Matter” present giving rise to the
gravitational field.” Nobody knows what this consists of or
even if it really exists, but that has not stopped reams of
speculation. Time will tell!
12
You said…
Michael said..
When the ‘fields’
Great question. Yes. The Dutch Metal device was called a
(protons from the
Gold-Leaf electroscope and its response allowed us to
balloon) react with
measure the strength of the electric field. This is
the sausage – there modified even by the glass on the front of the container,
must be a measure
but the extent of the change in the field is not very large
of strength – does
for materials like glass, or air. It can be very large for
this change if the
materials like water and metals.
‘field’ has to pass
through glass and
What causes the change? It has to do with how the atoms
metal – as the
and molecules within a substance react to the applied field.
Dutch-Metal (brass) If they have a strong response, then they affect the field
experiment?
strongly.
Great first session!
Glad you enjoyed it and glad you
Very interesting practical examples which I will be able to take some
can now use at home, so that’s objective no.1 experimental ideas home with you.
already achieved.
This week we will have more
Interested in more examples regarding the examples about the propagation of
propagation of EM wave e.g. light with
light and the relationship between
respect to atoms.
light and atoms.
Looking forward to next week. Me too
What does
Great question. It consists of – antimatter! Antimatter is ‘stuff’
antimatter
but very strange stuff indeed. Each of the particles I told you
consist of?
about has an antiparticle – a kind of ‘sciency doppleganger’ – with
opposite properties. So
 The antiparticle of an electron is called a positron, which has
the same mass as an electron, but the opposite charge.
 The antiparticle of a proton is an antiproton, which has the
same mass as a proton, but is negatively charged.
 The antiparticle of a neutron is an antiproton, which has the
same mass as a neutron and no charge just like a neutron.
The astonishing thing is that when an antiparticle meets its
particle partner they annihilate each other leaving nothing but a
burst of light!
So how did we discover them? We first saw them in experiments
using balloons to lift particle detectors high up into the
atmosphere and saw that they arrived at the Earth from outer
space. There are many mysteries about antimatter.
 Are they exactly the opposite of their matter particles?
 Why is world we know made of matter and not antimatter?
Fascinating stuff!
13
You said…
I loved the way you
started with scale.
When I think about the
scale of the universe I
feel terrified – but
thank you for making
me feel a little safer!
Do you think there are
other humans anywhere
else but Earth?
Michael said..
We often forget that ‘awe’ as in ‘awesome’ doesn’t
mean ‘great’ it means terrifying! I think your reaction –
terror! – is perfectly understandable. Give the size of
the Earth – which seems so large to us as individuals –
when we see the Earth in perspective to the rest of
the Universe it is profoundly shocking. But that is just
the way it is – and we need to keep on with our daily
lives.
I think there will be other life somewhere, but not
humans. Humans are perfectly evolved to live on Earth
– and we can never live anywhere else.
Can we be sure
These are the only types we have seen, And it raises the
there is only +ve question: what is electrical charge? And since you ask,
and –ve charges? electrical charge is a fundamental property of matter and we
What is the
can’t explain it in terms of anything else.
distance between The distance between the nucleus and the orbiting electrons
the nucleus and
varies from one type of atom to another.
the electrons.
 The nucleus is very tiny compared to the size of an atom.
In units of picometres (1 pm = 10-12 m) a nucleus is typically
0.001 pm in diameter.
 In a hydrogen atom which has just one proton and one
orbiting electron the average radius of the orbiting
electron is 53 pm.
 In heavier atoms there are more protons in the nucleus
and more orbiting electrons. The inner orbits are pulled in
very tightly towards the nucleus but the outer orbits are
usually a bit larger with a typical radius being ~ 100 pm.
Is there a
Well we don’t know of any definite minimum size, but there is
minimum size a
a length – called the Planck length after the scientist Max
particle can
Planck which marks a size at which we think our understanding
reach or do they will definitely run out! This length is approximately 10-35
keep getting
metres. It is difficult to conceive of this length but try this.
smaller and
The nucleus of an atom is around 10-15 metres in diameter, so
smaller?
the Planck length is smaller than a nucleus by a factor 1020 or
100 000 000 000 000 000 000
By comparison the nucleus is only a factor 1015 smaller than
you are. So (in principle) all the complexity of life which
exists between our everyday scale of life and the nucleus of
atoms (this includes consciousness, brains, life, children, etc )
all of this could exist on a smaller scale between a nucleus and
a Planck length. So to summarise, we can keep getting smaller
for quite a long time yet!
14
You said…
Really enjoyable,
very clear
visualisations.
Question: Is this
strong force
constant?
Very well
explained. Good
PowerPoint. Can
you explain the
interactions
between
molecules ever
further?
Michael said..
Thank you.
Answer. I am not quite sure what you mean. You could mean
‘Has it changed in time since the big bang?’ We don’t think so.
Or you could mean ‘Is it similar in strength between protons
and protons, and protons and neutrons?’ It does vary slightly,
but acts roughly equally between all protons and neutrons.
Glad you liked the PowerPoint slides.
Yes I can explain the interactions between molecules further.
It’s difficult to answer such a general question but it is
interesting to think about cases where we describe the
interaction between molecules as chemical and when we
describe them as physical. Think about two different types of
atoms approaching each other so their outer ‘valence’ electrons
come close.
 The key thing to think about is the strength of the electric
field.
 ‘Noble gas atoms’ such as helium, neon and argon are almost
perfectly spherical and have barely any electric field
outside the regions where electrons orbit. This makes them
chemically unreactive.
 All other atoms have relatively strong electric fields
outside the atoms and are not perfectly spherical. As atoms
approach each other, the outer (valence) electrons pick
which atom has the strongest attraction.
 If the electrons make a move from one atom to another we
call this interaction ‘chemical’.
 If the electrons stay with their original atom then we say
there is no chemical reaction and call the interaction
‘physical’.
 Often the division is a bit blurred and many interactions are
part-chemical and part-physical. But the key thing to
remember is that it is all about electrical interactions!
Does that make any sense?
15
You said…
How do you
change course
in a vacuum.
Michael said..
I think you are asking about how a rocket or satellite travelling
through space can change course. Assuming that the rocket is
not firing, the overall momentum of the rocket and all its
contents are fixed. If it is not acted on by a force such as
gravity, it will travel in a straight line with uniform speed – this
is Newton’s first law of motion. In order to change direction
(say to the right) some part of the rocket has move to the
left. To do this a rocket shoots hot gas to the left.
The momentum of an object is its mass × velocity. In order to
change direction using the minimum amount of mass, the gas is
made as hot as possible so that its molecules move as fast as
possible.
Thank you for a great first lesson.
You are welcome.
“what fun
So many fun investigations to do with electricity. One thing I
investigations
have tried with mixed success has been making a Kelvin
could someone do Water Dropper. If you a keen DIY-er it is quite do-able in an
with
afternoon
electricity?..?”
“.... or anything
http://en.wikipedia.org/wiki/Kelvin_water_dropper
to do with
physics... that
Other wise I have been thinking a lot lately about what makes
wouldn’t result in things sticky… lots of experiments to try there!
death?”
When I tried to visualise one Mmmm. Well observed. The answer is that I think
tenth of a millimetre I saw:
so. We will talk more about diffraction this
evening. Why am I not sure? Because I couldn’t
photograph this effect. I tried with a microscope
and a conventional camera and they don’t show the
extra lines in between the upper and lower finger.
I suspect this is a mixture of two effects, one
Is this a diffraction effect? connected with diffraction and the other
connected with some detail of human vision.
I am a last minute substitute for a geeky
I am glad you enjoyed yourself.
father and would have said I was not that
This is not the first time this has
interested in science.
happened! But I trust you and the
I have thoroughly enjoyed this evening and
geeky father will sort things out
am looking forward to the rest of the course! amicably.
It was an extremely
That sounds excellent. I like the way you specify
good session, I’ve learnt learning things you didn’t know before! At my age I
a lot and many things
take pleasure in learning things I didn’t know before
I’ve never known
but also in re-learning things I did know before – but
before.
have somehow placed to the back of my mind.
16
You said…
Michael said..
I have learnt a lot from this week and
It is a remarkable story and there
learnt it in a fun and enjoyable way! It
are many more fantastic stories
really lets me think how electricity works
about the key breakthroughs.
and how people found it!
Very entertaining and informative. Thank you.
You are welcome 
Excellent!
I am blushing again 
Where does Dark Well nobody knows! At the moment I think the basic
Matter fit in the assumption is that ‘Dark Matter’ is a new kind of ‘stuff’ i.e.
‘Stuff’/’Not
particles – of which we were previously unaware. I have
Stuff’?
heard people suggest it could be a kind of ‘not stuff’ i.e. a
Great evening!
field – of which we were previously unaware, but doesn’t seem
Thanks.
to be the vogue. As I explained somewhere else in these
notes, we think ‘Dark Matter’ exists because of its effect on
the motion of stars in galaxies. It could be that it doesn’t
exist – but we just don’t understand something else about the
motion of stars. The thing is – nobody knows!
What does quark People don’t know what if anything makes up quarks.
consist of?
 Quarks were discovered at the Stanford Linear
Highly
Accelerator (SLAC) in California – a straight version of
entertaining and
the LHC. The LHC smashes protons into other protons,
intriguing – as
but the SLAC smashed electrons into a target made of
well as grasping
liquid hydrogen and looked at the angles at which the
my attention, it
electrons emerged.
really boosted
 Hydrogen is made of single protons, single electrons and
and reinforce my
lots of space, so most electrons go straight through the
understanding.
target.
I’m looking
 We have never discovered any structure inside an
forward to the
electron – it behaves like a squishy ball of electric charge.
next!
So if protons were just point-like particles the scattering
pattern of the electrons could be predicted.
 In fact people saw that occasionally electrons seemed to
be scattered by tiny ‘hard’ point like-scatterers inside
each proton.
 We have never discovered what makes up quarks but
perhaps at some time we will.
Thank you. It was great.
You are welcome 
Best explanation of fields I
Thanks you, what a lovely thing to say.
have ever listened to, thanks.
17
You said…
Michael said..
V. informative. Had a good
I am glad you understand the links between
understanding before but now
chemistry and physics. Culturally, and in their
appreciate the links between
nomenclature, Physics and Chemistry are quite
physics and chemistry better.
distinct, but of course they are both describing
Good P.P.
the same physical reality.
Excellent demo – engaged
Glad your daughter enjoyed it and
daughter and helped
congratulations on her engagement.
understanding.
It’s amazing to think of myself Indeed. The complexity of what lies within us
as a macro-Universe of billions and size of the Earth and the Universe is …
and billions of particles and
amazing and awe inspiring.
fields.
It is cool that I have electricity in me.
Indeed.
An atom is made out of
If our culture collapses and you are the last
protons, neutrons and
person alive – pass this on to your children – it is
electrons.
an astonishing discovery.
Good. I really enjoyed
That level of complexity is exactly what I strive for. I
it – complicated enough have struggled for years to get it right and it is not
to be interesting, but
there yet. In particular I find it very hard not to say
not too complicated to extra things – qualifying each statement. In terms of
be past me. Thank you! the oath taken in the witness stand, I promise to tell
I really liked the
the truth and nothing but the truth – but I can’t tell
different way of
the whole truth – otherwise you would be bored rigid!
drawing the periodic
Yes it is interesting to see that there are other ways to
table, and the film was represent the periodicity.
very interesting and
eye-opening.
Really brilliant
Glad you enjoyed it.
evening!
I think you mean why did the electrons that got rubbed off
Why do the
my pullover onto the balloon stay there?
electrical charges
 The answer is that they were trapped on the balloon
that get moved to
because the rubber of the balloon is an excellent
make ions stay
insulator.
there?
 They don’t stay trapped on the balloon indefinitely
because the rubber and the air are not perfect
insulators. In particular there are lots of dust particles
in the air and molecules of water that are strongly
attracted to the charges on the surface on the balloon.
 These processes slowly reduce the concentration of
charge on the balloon.
18
You said…
Very
interesting and
helpful and
well explained.
I’ve never seen
the other
format of the
Periodic Table,
are the
different
groups the
same just
arranged
differently?
I enjoyed the
experiments
outside too.
Thank you.
When you put
the slide up of
the periodic
table on the
right hand side
there was a
second
diagram. What
was it?
Michael said..
There are lots of other periodic tables. Try Wikipedia on the
subject:
http://en.wikipedia.org/wiki/Alternative_periodic_tables
or just search Google with the search term “Alternative
periodic tables”. These alternatives generally try to represent
the fact that the periodicity in the elemental properties arises
from the physical structure of electron orbits around atoms by
having some kind of circular structure.
The periodic table reflects the periodic physical structure of
atoms with increasing numbers of protons and balancing
electrons.
 Electrons orbit the nucleus in specific orbital patterns and
some numbers of electrons can make a perfectly spherical
closed ‘shell’ of charge. This is a configuration which has a
very weak external electric field and so is chemically very
un-reactive. Atoms with this configuration are
o Helium (He)
o Neon (Ne)
o Argon (Ar)
o These elements all have similar chemical properties
 Adding one proton and balancing electron makes an atom
which has one electron orbiting a closed shell of charge. This
one electron has a strong external electric field which makes
these atoms chemically very reactive. These elements are
o Helium + 1 proton and electron = lithium
o Neon + 1 proton and electron = sodium
o Argon + 1 proton and electron = potassium
o These elements all have similar chemical properties
19
You said…
 Good jokes.
 I like the Tonight’s
Drama thing.
 Need to be more
prepared about the
songs.
 Good presentation.
Good experiments – but
could not see it all
clearly. Explanations
were clear.
 I want to hear the song
of elements.
 What is the chemical
formulae of gold? Is it
chloride and
something?
Michael said..
 Jokes? Were there any jokes?
 Glad you liked the drama thing: that was a new
slide – I don’t add slides easily – I prefer to take
them away and try and say less.
 Yes, it’s normally the ‘live’ bits that go wrong. In
this case the Flash player has changed how it
handles files between the last presentation and
now!
 Part of the problem was that at 4:30 a.m. the
next morning I left to visit the European Space
Agency in the Netherlands and I had spent the
day preparing for two things instead of just one,
and I missed my usual ‘click through’ before we
started.
 What could you not see clearly? Please let us
know and we will make sure you can see.
 You will hear the elements song this week!
 Gold is an element with the chemical symbol Au.
It’s nucleus has 79 protons and 118 protons and it
is orbited by 79 electrons. No it’s not a compound
with Chlorine.
I liked the video of zooming in and out from the
Yes, that is great video. If
man’s hand across the universe.
you look on-line I think you
I found the session fun and interesting. I have no
can see how it was made
current questions about this topic of electricity.
and that is even more
However, I do have a more life related question:
amazing.
What jobs are available at NPL? And how do I go
Regarding work experience
about applying for them? I am just finishing my
and things you should just
GCSEs so probably won’t be applying in the
cold-call people: they can
immediate future unless you do work experience or
only say no!
apprenticeships.
20
You said…
Thanks Michael for making
it so accessible and
interesting and fun.
Question: Nothing to do
with electricity I suspect.
Blue bubble bath makes the
water blue buy the bubbles,
however deep a handful are
always white not blue.
Surely lots of thin tiny, tiny
layers should be blue?
Nights of pondering over a
pint at university and in
decades since have never
given me an answer. Can
you?
Michael said..
You are welome
Answer: Well observed. The answer is connected
with electricity because it is connected with light.
It has to do with light ‘scattering’ – and hundreds
of reflections.
 Think about glass or water which is mainly
transparent. However most glass reflects about
4% of the light that falls upon it.
 Similarly water surfaces reflect about 4% of
the light that falls on them. We can see this if
the water surface is still – think about
moonlight on the sea.
 The colour of the reflected light is the same as
in the light source.
 Bubbles are made up of lots of surfaces and not
very much liquid. So light which falls onto
bubbles such as in a bubble bath undergoes lots
At about age 6-7 (still at
of reflections. Initially 4% is reflected leaving
Infants School) my son’s
96% to travel onwards. At the next surface an
question over tea was “So
another 4% of that 96% is reflected. After a
Mum, if you’re at the top of
few hundred reflections the light ends up
a mountain you’re nearer
travelling in all kinds of directions, but has
the sun so why is it
pretty much the same spectrum as it did
colder?” It took months of
initially. So if you illuminated your bubbles with
questions to everyone I
white light, then bubbles will look white.
knew till he got an
 The light does travel through a thin wall of the
acceptable answer. His
bubble which is made of liquid. In a ‘blue’ liquid,
questions and interests
the red light will be absorbed and the blue light
haven’t stopped yet.... And
transmitted. But because bubbles are mainly air
he’s planning on Physics,
and very little liquid, the colouring of the light is
Chemistry, Maths, KT Anot very strong. Hence bubbles of all liquids –
levels so that’s probably
bubble bath or beer – are pretty much white.
why. Hopefully the next six  That is a great question and I am glad your son
weeks will give him lots
got to the answer eventually – and good luck
more questions too!
with his A levels!
Feedback: Non-choc
 We had a biscuit emergency last week – a
biscuits would be nice as
delivery didn’t arrive and the Amey staff had to
I’ve given up choc for Lent.
run out and buy biscuits from Tesco! This week
Guess I’ll wait till week 6!
I expect more variety.
Really interesting and mind boggling!
Excellent!
Thank you.
You’re welcome 
21