Download Protons for Breakfast

PROTONS FOR
BREAKFAST
AUTUMN 2013
WEEK 2
LIGHT
1
This is what you said on the feedback forms in Week 1
You said…
Michael said…
 You have obviously got  I do indeed have a vast library of songs and recently
a vast and fantastic
they have become available on iTunes. Details here:
library of science
http://protonsforbreakfast.wordpress.com/songs/
songs. Please could
but don’t look if you want the songs to be a surprise
you provide links to
each week .
them.
 No, fields are not made up out of particles of ‘stuff’.
 Are the fields made
We will look at this again this week. And
up of electrons?
demonstrate the nature of fields with Jelly babies.
Qu: Can you
Mmmm. I am not quite sure I have got the gist of this.
demonstrate electrical  I think you are saying that if after rubbing the balloon
repulsion using your
on my pullover, I had taken off my pullover, would the
jumper instead of the
paper have been repelled rather than attracted?
balloon, or would the
 If that is your question then the result would be the
paper rotate and still
same. Why? Because overall the paper remains
be attracted but on
electrically neutral. And the balloon (or pullover) acts
the opposite side. If
to polarise the paper – i.e. to induce a tiny separation
so can you colour each
of charge., rather than to add or subtract charges
side to visually
 If I had used my pullover rather than the balloon, my
represent the
pullover would have been oppositely charged compared
rotation.
to the balloon and would have induced the opposite
polarisation than that induced by the balloon. And the
net result would still be an attraction.
2
You said…
Michael said…
I like the
 I think this distinction is very important for appreciating
distribution between
‘how the world works’. One can’t make sense of things
matter and fields as
without appreciating this fundamental ‘duality’.
two different kinds
 ‘Action at a Distance’ was the phrase used to summarise –
of ”entity” that
indeed mock – the concept of a ‘field’. At the start of the
exist in “space|”.
19th Century people could only envision a force being
Q: Can we
communicated by direct contact. It was really James
understand action at
Clerk Maxwell who understood that the electric field was
a distance, or just
real. This gave rise to the ‘three-step process I
describe it in
described.
mathematical ways?
o A particle with a property we call electric charge
(I’m not sure this
disturbs the field in its immediate vicinity.
makes sense!). What
o The disturbance – or wave – travels away
is a “field”?
o And a short time later, other particles are affected by
their local field.
 I think we do understand it, but not completely. And in
some sense we can only describe the world and say what
fields are ‘like’. In a fundamental sense, we can never
know what either fields or particles ‘are’.
All really interesting!
I am glad you found it so.
How quickly
It depends on the atmosphere. If the atmosphere is dusty or
does a charge
moist, then electrical charges on the balloon can polarize
piece of paper
microscopic dust particles – attracting them, and then when they
lose its charge? touch the balloon, they become charged and then repelled,
carrying away the charge. In normal air it typically takes a few
hours, but occasionally things can stay charged for days – we
still had ‘floating foil’ pieces stuck to the ceiling for a whole day
after last week’s session.
 How is the strong
 When I said ’it’s all electricity’ I was speaking of the
force different
forces which we experience around us: i.e. chemistry,
from electricity?
biological processes, mechanical forces etc. are all
If it’s all
fundamentally electrical in nature.
electricity, what is  We do not know of any connection between the strong
the strong force?
nuclear force that acts between:
 Looking forward to
o protons and protons,
the answer next
o protons and neutrons, and
week – thank you
o neutrons and neutrons.
for this evening.
And the electric force. They are – as far as we know
fundamentally different.
 The strong force is very short range. So that it acts in
effect like a ’contact’ force – as if the particles had a
sticky surface.
3
You said…
I like the toys.
What is the strong
nuclear force?
How much static
electricity does it
take to move a
human?
Michael said…
 Glad you liked the Fun-Fly Sticks.
 I have written an explanations of the strong nuclear
force both above and below this answer!
Mmmm. Not sure what you mean here.
 If I applied a few nano-coulombs of charge from a Van der
Graaff generator, then the flow of electricity would cause
you to feel pain, and the resultant muscle contractions
would make you move. Perhaps that is not what you meant.
 If I hung you on a balance like I hung the sausage, then I
could move you with just a single balloon rubbed on my
pullover. The force would be very similar to that on the
sausage, but because you are so much heavier, you would
accelerate slower. However you would eventually swing
around! The largest thing I have accelerated in this way
was a guitar weighing around 10 kg.
By week 6 will I be able to converse with Brian Cox?
Yes 
When an
We will talk more about isotopes in week 6. But briefly, no, more
atom has a
neutrons do not always make an isotope more stable. For atoms with
higher
small numbers of protons, the optimum number of neutrons is the
isotope
same as the number of protons. So for example, the main stable
(more
isotope of carbon has 6 protons and 6 neutrons and is called 12C
neutrons)
where the ‘C’ tells you it is carbon and so has 6 protons and 6
does it mean electrons and the ‘12’ tells you that the total number of protons and
that it is
neutrons is 12 i.e. that it has 12 – 6 = 6 neutrons.
more stable?  If you take away a neutron to make 11C then the nucleus falls
apart after about 20 minutes.
 If you add a single neutron to make 13C then the nucleus is stable
and this isotope makes up 1.1% of all the carbon around us.
 If you add two neutrons to make 14C then the nucleus is unstable
and the nucleus falls apart after about 6000 years.
So too few or too many neutrons makes the nucleus unstable.
For heavier elements, such as gold (Au) which has 79 protons, the
nucleus needs more neutrons to act a nuclear glue to hold all the
protons together. So the only stable isotope of gold is 197Au which
has 197 – 79 = 118 neutrons. However adding (198Au) or subtracting
(196Au) a single neutron makes the nucleus unstable.
Atoms with unstable nuclei are said to be ‘radioactive’.
4
You said…
 Comment - loved
doing the demos at
coffee break!
 Question - Why is
the middle of the
periodic table
shown separately?
 Thought - I feel
much better
knowing there are
only 2 kinds of
thing in the
Universe that I
have to understand
(i.e. stuff/nonstuff). Learning
about science
seems much less
daunting now!
(That’s not sarcasm
either!). Thanks for
a great evening.
Michael said…
 Glad you enjoyed it.







Great Question: The Periodic Table shows elements in
order of the number of protons in the nucleus of the
element (called the atomic number). It starts at the
top left (H) and reads left to right, and then we go
down a row.
The shape of the conventional diagram reflects the
way electrons arrange themselves around the nuclei of
atoms in so-called ‘shells’.
Let’s imagine creating new atoms by adding protons to
the nucleus, and corresponding orbiting electrons. We
start with hydrogen (H) which has 1 proton and 1
electron, then make helium (He) which has 2 protons
and 2 electrons. 2 electrons form a closed-shell i.e.
the orbits make a perfect sphere.
As we add more protons and neutralising electrons, the
electrons arrange themselves around the first closed
electron shell – but it now takes 8 electrons to
complete this 2nd shell (Ne). These closed shell
elements are chemically similar (and very un-reactive)
and they are plotted on the right-hand side of the
table.
The next shell also takes 8 electrons to complete (Ar).
The next shell permits more complex orbital
trajectories and can accommodate 14 electrons. The
elements with the complex orbitals – called d-orbitals –
are plotted in the middle of table.
After that – it gets ‘even more complicated.
5
You said…
Michael said…
Very interesting – I
 Thank you. That comment makes me at the same time
learnt more tonight on
happy, but also sad!
the subject that I did  ‘Fun-Fly-Sticks’ cost £20 and we buy them from
http://www.grand-illusions.com/acatalog/FunFlyStick.html
at school!
which is a British company which pays tax. They are
How much does the
available cheaper from Amazon.
portable VDG
generator cost?
Well explained.
 Thank you.
God said he created
 I am not aware that we have God’s authentic voice on
everything at the
any issue, but there are many competing and conflicting
beginning, would
human claims to represent ‘him’.
dinosaurs have been
 Dinosaurs existed more than 65 million years ago.
alive with humans such
Humans have only existed for the last 1 million years or
as in times like end of
so, and the regular advance and retreat of the polar ice
Triassic period and
that we call ‘ice ages’ have only been taking place for
early ice age.
probably a similar period.
You said about
Yes, exactly correct. As we pack extra electrons around an
valancies in the
atom they ‘stack’ in so-called ‘shells’ at different distances
talk. Are they the
from the nucleus
different amounts
o the first shell can accommodate 2 electrons and the
of electrons in the
element with the filled shell is non-reactive helium.
outer shell of an
o the next shell can accommodate 8 electrons and the
atom, with the
element with the filled shell is non-reactive neon.
shells having 2, 8,
o the next shell can accommodate 8 electrons and the
8 etc per thing?
element with the filled shell is non-reactive argon.
And the ones with
o the next shell can accommodate 18 electrons and the
complete outer
element with the filled shell is non-reactive argon.
shells are
 I feel obliged to say that the patterns that electrons
unreactive as they
make as they orbit nuclei are complicated, but this simple
can’t form ions
representation is a fair summary.
right?
 The thing which makes them unreactive is that the filled
shell is completely spherical symmetric and so nearly
perfectly cancels out the effect of the electric charge on
the nucleus in every direction. Unfilled shells are not
symmetric and there are ’gaps’ though which the nuclear
charge can be detected by other atoms – pulling them in
for an electrical interaction that we call a ‘chemical
reaction’.
6
You said…
How many
protons/electrons
are there in a
banana?
How many
electrons are
there in a
sausage?
Very good speech
– detailed,
understandable
and informative.
Loved the
experiments.
Michael said…
I have just weighed a banana – a large one – and it weighed
0.243 kilograms. Scientists have worked out the protons and
neutrons weigh roughly the same – approximately:
1.66 x 10-27 kg
Electrons weigh approximately 1/2000th of the mass of a
proton or neutron so we can neglect their mass in this
calculation. So the total number of protons and neutrons in
anything weighing 0.243 kg is roughly;
0.243 kg ÷ 1.66 x 10-27 kg = 146 x 1024



If we assume this number is roughly half neutrons and half
protons – which is pretty accurate for a banana made mainly
of oxygen and carbon – then a banana contains
approximately 73 x 1024 protons. I am pretty sure that
answer is within 10% of the correct answer.
You can do the same calculation for a sausage – but I will
leave that up to you – it depends on the mass of the
sausage.
Glad you enjoyed it 
7
You said…
 Really enjoyable,
entertaining and
very informative.
 My question: Do
fields – electrical,
gravitational always
behave in the same
way irrespective of
their surroundings.
Are they affected
by, for example,
pressure. Would an
electrical field be
the same at the
bottom of the
ocean or deep in
the earth as it is
with no pressure –
or even in space?
Michael said…
 I am glad you enjoyed it.
 Mmmm. I am not sure how to answer this, but here we
go.
Imagine two charged particles, both positively charged
– so they repel each other. Imagine they are in a box
which is evacuated so it has no air inside.
 Then it wouldn’t matter where that box was: in the
deep ocean or deep space:– the force between the
particles would be the same.
 However if you let some atoms into the box, then they
would be affected by the electric field, and in return
they will then affect the electric field, and so the
force between the two charged particles would be
slightly modified.
OK. Now I get it!
Great ;-)
Why do some
 Both the normal arrangements (6 protons and 6 neutrons) and
carbon atoms
the rare arrangement (6 protons and 7 neutrons) are stable.
have seven
So when the elements were formed, they stayed the way
neutrons rather
they were.
than the usual
 When were the elements formed? Well:
six.
o The nuclei of nearly all the hydrogen and helium in the
universe was formed in the first few seconds after the Big
Bang, This includes all the hydrogen atoms in the H2O in
your body. Does that make you feel old? Because the
protons in all the hydrogen atoms are around 13 billion
years old.
o The elements lighter than iron were subsequently created
inside stars (this is where the carbon came from), and when
the stars exploded they were scattered into clouds of dust
o The elements heavier than iron were created during the
stellar explosion that scattered elements into clouds of
dust
o We are literally (as Joni Mitchell sings) stardust.

8
You said…
I want a fun fly stick!
Feedback: I like
the extensive talk
about the subjects.
Especially about the
atoms because it will
definitely help me in
school.
Questions: What is
the reason why
atoms can only hold
82 protons before it
becomes
radioactive?
Overall: I loved the
experience, and
can’t wait to return
next week.
Michael said…
Everyone does, me included. But to be brutally honest –
there is only about an hour or so of real play value in these
things – so you have probably had the best of it already 
 Good. Happy to help.
The limit comes from the balance of the electrical
repulsion and the strong nuclear attraction. Consider the
case of a proton on one side of the nucleus. Because
electric repulsion is a long range force, the ‘edge’ proton
feels the repulsion of all the other protons. This
repulsion is shown by double ended arrows in eth picture
above.
 It is bound into the nucleus by the strong nuclear force
which is a short range force – essentially a contact force.
The ‘edge’ proton is held in place by at most 9
neighbouring neutrons. As we add more and more protons
the repulsion gets bigger and bigger, but the binding
force can’t keep growing because the ‘edge’ protons can’t
make contact withany more neutrons.
 Above 82 protons (Lead), it isn’t possible to find an
isotope with a perfectly stable arrangement. Element 83
(Bismuth) is long lived, but not quite perfectly stable.
 Thank you. I am looking forward to it too.
The dogma is that:- I am afraid I can’t understand this.
DNA makes RNA
My guess is that you are commenting about some aspect of
make PROTIENS!
our understanding of how biological cells function. In
So, how come:- DNA particular on the mystery of how archaic cells are thought to
makes RNA make
have evolved using RNA only but now cells use bothe DNA
PROTIENS?
and RNA.
I am not the right person to comment on this – personally I
think it will take a while before we get all this sorted out.

9
You said…
Michael said…
 Questions: Do you see a parallel between  Mmmm. Tricky.
the fact that matter and anti-matter
 The universe as we find it has
must exist together, but being kept
only the tiniest amounts of antiapart, otherwise cancel each other and
matter. And I am not expert on
the Bible’s description of Heaven and
Biblical interpretation, but I don’t
Earth?
entirely see a parallel. Maybe I
 Maybe a parallel between how the tiniest
have missed your point. Sorry.
particles behave and how our universe is
set apart into two worlds is possible?
 Here is the Powers of Ten Video
http://www.youtube.com/watch?v=0fKBhv
 Can I show the Power of Ten’s video to
Djuy0
my son? Is it available on the internet?
 We will indeed go deeper: glad
 Feedback: Great overview, hope we go
you enjoyed it.
deeper. Memorable lessons.
Very interesting presentation,
Glad you enjoyed it. The periodic table is a
learned lots. Great to see a periodic great cultural icon – a tremendous
table after 25 years!
achievement our culture.
 How many atoms thick
 250 sheets of printer paper is approximately
is the thinnest sheet
50 mm thick so I estimate that 1 sheet of printer
of paper?
paper is 50/250 = 0.2 mm.
 Also great
 The spacing between atoms in most substances is
presentation. Michael
about 0.3 nanometres, so the sheet paper is about
is so funny! It would be
1 million atoms thick.
great to have him as
  For a few weeks at least I think I am your
my science teacher!
science teacher.
In a field,
Great question and we will discuss this more this week, when we use
what is
the giant Jelly-Baby wave machine.
actually
 The behaviour of a ‘field’ is like the surface of a pond.
moving?
 When you poke a stick up and down in a pond – a wave travels
away from the stick across the surface.
 Water isn’t travelling away from the stick. The water level at
each point on the surface just moves up and down, but the
disturbance is passed from each region of the wave to its
neighbouring region and so travels away from the origin.
 In this way a disturbances spreads even though each part of
the surface just moves up and down.
10
You said…
 Why is an

Angstrom 1010? Not a
multiple of 3!
10-9, 10-6, 10-3,
100?

 If everything is
electrical what 
about neutrons?






Michael said…
An Angstrom (symbol Å i.e. an ‘A’ with a ‘diacritical’ mark)
is a unit of length named for Swedish physicist Anders
Ångström (1814–1874). Though still widely used,
particularly by chemists, it is not part of the International
System of Units (the ‘SI’) and so is an obsolete unit.
As you noticed, the SI uses special prefixes to give names
to units which differ in magnitude by a factor 1000.
I think I mentioned this somewhere above. You are quite
right that within the nucleus of atoms both electricity and
the strong force are important.
Why have you got
 Yes, they are cheaper to run and should last for 25
new LED lights?
years. They can be much brighter than they are. When
- are they cheaper
they were commissioned, their brightness was
to run?
measured and turned down to give just the correct
- are they brighter
level of illumination.
than the old ones?
 What do you mean by ‘electricity and water don’t mix’’?
If electricity holds
In our homes we keep electricity quite separate from
water together
water. That’s because water is an electrical conductor
why don’t
and so if water spilt, electricity could flow into
electricity and
wherever the water went, which could be quite
water mix?
dangerous. But the fact that water is an electrical
conductor arises from its intrinsic electrical
properties.
Will look at the world in a
 Great…I think. As long as you are
completely different way.
happy with the new view.
Have scientists ever thought of
 I don’t think so. Because the word
giving the word ‘electricity’ a
comes from the Greek, it has been
different name. It is such a
inherited more or less directly into all
universally important concept, and
modern languages.
in my mind not completely
 It is definitely not appreciated how
appreciated.
amazing and universally important the
concept is.
11
You said…
 What size is the
Milky Way to the
Sun to the Earth to
the moon?
 Cause in the first
video the Milky
Way was further
than the Sun and
yet almost the
same size as the
sun and moon when
I’m standing on
Earth.




What is the strong
force?
Why are protons
and electrons
charged?
Why don’t neutrons
have a charge?
How much does one
of those ????
things cost?
Where can I get a
magic wand…?
Michael said…
Not sure exactly what you are asking. I think what you are
commenting on is the angular extent of an object. For
example, when you hold out your thumb at arm’s length,
you can block from view:
 A 0.5 metre-wide person 50 metres away
 The 3400 kilometre-wide Moon 380,000 kilometres
away
 The 1.4 million kilometre-wide Sun 150 million
kilometres away
In each case the blocked object has a diameter of around
1/100th of the distance to the object
Our estimate for the size of Milky Way is uncertain
because we are right in the middle of it, but we think it is
about 100,000 light years in diameter but only (!) around
1000 light years thick.
 I have answered this a couple of times above and
below. Briefly the strong force acts between:
o protons and protons,
o protons and neutrons, and
o neutrons and neutrons.
 Great question. Fundamentally, we don’t know what
electric charge ‘is’ – we can’t explain it in terms of
anything else – it is a fundamental property of the
‘stuff’ of the universe.
 As I mentioned somewhere else – electrons are – to the
best of our knowledge – truly fundamental particles: no
matter how hard we bash them together, we don’t see
evidence of any internal structure.
 Protons and neutrons are each composed of three even
tinier particles called quarks. Quarks too possess
electric charge, but in a neutron, the quark charges
add up to zero, while in a proton they add up to make a
charge we observe.
 Glad you enjoyed the experiments. The Fun Fly Sticks
cost about £20 – a web link is given somewhere else in
these answers.
I think you mean a Fun Fly Stick – I put the links
somewhere earlier in this document.
Magic? It’s not magic, its science, which is IMHO just as
cool – if not cooler – than magic.
12
You said…
 Why is there 
a charge?
 Where does
it come
from?

 How are
electrons and
neutrons and
protons

made?
Michael said…
As I mentioned above, fundamentally, we don’t know what
electric charge ‘is’, and we can’t explain it in terms of
anything else – it is a fundamental property of the ‘stuff’ of
the universe.
We don’t know where it comes from but we do know that it is
‘conserved’ - we can’t get rid of it! And there seems to be an
equal amount of the positive charge and negative charge in
the universe – coincidence? I think not!
In our current understanding, all the protons and neutrons in
existence now were formed about 2 seconds after the big
bang. The electrons were formed a few seconds later.
Obviously you can ask – How can we possibly know stuff like
that ! And of course we don’t. But we can say: If the big bang
happened as we think it did, how much hydrogen and helium
would we expect to find in the universe? And when we do the
calculation we find a very reasonable match with what we
observe – which makes us think that we must at least be
close to the right idea.
Yep! You were right. I’m boggled. Wow!
Boggled is OK as long as you are not
Thank you.
panicking.
 Great presentation –  Thank you and well done for re-visiting the exam. It
wish I’d had that 50
is interesting to me how long your memory of having
yrs ago when I failed
‘failed’ persists. Based on your comment, you must
physics O level
now be 65-ish and yet this ‘failure’ still sounds like it
(passed 2nd
is somehow alive. As you may know, in the last 50
attempt!) (But still
years, schools have become obsessed with exams and
pretty boggled.)
I worry about the large numbers of citizens that can
 Q: Why does light
feel that sense of failure and thus perhaps exclusion
sometimes seem to
from ownership of science. Which is wrong, because
“bend” round
if you are a citizen of the UK, your taxes over the
objects? Is it due to
last 50 years have paid for pretty much all the
the electric charge
science in the UK: in other words: it’s yours!
of the object?
 Excellent observation. The phenomenon is called
diffraction and arises because light is a wave. For
light, yes, the electric charge within an object is
involved. We will look at this week. You can observe
other waves diffracting: sound diffracts easily which
is why we can ‘hear around corners’; and water waves
in the sea diffract around islands and headlands.
13
You said…
 If you flipped
electrons and
protons would
things be
different?
 It was
electrifying.
Michael said…
 Assuming by ‘flipped’ you mean we somehow instantaneous
replaced every proton with an electron and vice versa: yesthings would be very different.
o The nucleus of every atom would be composed of neutrons
and electrons. The strong force does not affect electrons
– they only feel the electro-weak force, and so the nuclei
of every atom would instantly fall apart.
o Some of the neutrons would meet the protons and form
new nuclei. But the repulsion between the protons means
that heavy complex nuclei would not form – they are only
formed at very high temperatures and pressures inside
stars.
o Finally electrons would begin orbiting the new nuclei.
o The net result is that basically the whole world would end
up being made of hydrogen. So yes, things would be
‘different’.
 Glad you enjoyed it.
14
You said…
Can you explain
the means by
which electricity
is measured e.g
watt, volt, amp,
ohm, etc please.
Thanks.
Michael said…
 It’s complicated, but you did ask!
Three of these units (volt, ampere and ohm) describe the ‘flow’
of electricity which is described by analogy with the flow of
water along a pipe under gravity. For water flows:
 The ‘current’ is the amount of water passing one point in the
pipe per second. This is analogous to the amount of
electrical charge passing a point in a wire per second
 Tilting the pipe gives the water more energy for each extra
distance the water flows. The extra energy per unit mass is
analogous to electrical voltage, which is related to the
energy per unit charge.
 The resistance of a pipe makes it hard for water to flow.
Similarly the electrical resistance of a wire describes how
hard it is to pass a given electric current
Coulomb: The unit of electrical charge is called a Coulomb. One
Coulomb is a massive amount of electricity – the experiments
with the balloons typically involved a few nano-coulombs and an
individual electron has a tiny charge 1.6 x 10-19 coulomb.
Ampere (or ‘amp’ for short): when one coulomb of electrical
charge per second flows along a wire then we say a current of 1
ampere is flowing. Because the charge on each electron is so
tiny, this involves the motion of massive numbers of electrons.
Volt: when some electrical charge has flowed far enough so
that its energy has changed by 1 joule for every coulomb of
flowing charge, we say it has flowed through a ‘potential
difference’ of 1 volt. So in a 9 V battery, the electrons leaving
the – terminal flow ‘downhill’ to the positive terminal and for
every coulomb of charge that moves along the wire it gains 9
joules of energy
Ohm: The electrical resistance of wire is measured in ohms. If
it takes a voltage of 10 volts to drive 2 amperes of current we
say the electrical resistance is 10÷2 = 5 ‘volts per ampere’ or 5
ohms.
Watt: A watt is a unit of power (not necessarily electrical)
which specifies how much energy (joules) per second a process
uses. If a 240 volt mains source passes 4 amperes through a
resistance then it will dissipate V x I = 240 x 4 = 960 watts or
just under 1 kilowatt.
15
You said…
Good
presentation.
Can you give a
summary of
the half-life
of elements,
e.g. uranium?
Michael said…
In elements with unstable nuclei, not all the nuclei decay at same
time. There is a uniform chance per unit time that a nucleus will
undergo a change to a new configuration of protons and neutrons.
 Some nuclei are very unstable, and the chance per unit time of a
nuclear change is high, so that only a few atoms of the
substance can exist on Earth at any one time.
 Some nuclei are nearly stable, and the chance per unit time of a
nuclear change is low, so that we can still find lots of the
substance on Earth even billions of years after the elements
were created.
Scientists summarise this chance per unit time of a nuclear change
by specifying the time during which on average half the atoms of
particular substance will decay: the half-life: For Uranium (U):
 232U has a half-life 68.9 years
 233U has a half-life 159 thousand years
 234U has a half-life 245 thousand years
 235U has a half-life 700 million years
 236U has a half-life 23 million years
 238U has a half-life 4468 million years
Because of this, most natural uranium we find on Earth now is
mainly 238U. Other isotopes may exist but their half-lives will be
very short – days, minuets or even small fractions of a second!
 More in Week 6
 Great, really enjoyed it.  Good 
 If the number of
 We don’t create water, but we can move it around
electrons are all already
and make it appear at convenient places – such as
in existence how do we
coming out of taps! So it is with electricity. Using
generate Eeeeee-lecbatteries, generators, conducting wires and
tric-ity.
insulators we channel electricity to appear just
where and when we want it.
Thanks for making ‘electricity’ so entertaining!!
You are welcome
Wish science was/had been taught like
Me too. Perhaps it will be one day 
this at school!
How many electrons do There are various estimates, all highly uncertain. The
we think are in the
basic approach is to neglect everything other than
universe?
hydrogen, and then estimate the number of atoms in an
average star, the number of stars in the average galaxy,
and the number of galaxies in the observable universe. Of
course we have no idea about the un-observable universe.
But in the bit that we can look at we think the number is
1080-ish but a factor a million either way is quite plausible.
http://bit.ly/16SAUay
16
You said…
What is the
strong force?
Michael said…
This is the force between:
o protons and protons,
o protons and neutrons, and
o neutrons and neutrons.
It is not a long range force like electricity, but instead just acts
between neighbouring particles – like a super-strong contact
‘glue’ making the particles stick together
What keeps
Do you mean “What stops electrons flying off into space?” or
electrons in
“What stops electrons spiralling into the nucleus?”
orbit around the  “What stops electrons flying off into space?” Basically the
nucleus? Is it
electrical attraction of the nucleus – the electrons just can’t
centrifugal
get away.
force – Earth
 “What stops electrons spiralling into the nucleus?” This is a
around the Sun?
much harder question which stumped people for decades.
Obviously electrons don’t do this – otherwise atoms would not
exist. Now we understand that although the force between
electrons and protons within an atom is exactly the same as
the one between the balloon and the paper, the laws of
motion of small particles are not the same as Newton’s laws
of motion which govern large objects.
 Tiny particles such as electrons obey the laws of ‘Quantum
Mechanics’. In quantum mechanics the electrons find stable
‘orbits’ and ‘trajectories’ which balance the kinetic energy
and potential energy.
Loads of ‘Wow’
 I am glad you had some ‘Wow’ moments. To be honest, I
moments. I am
was exhausted and fed up before I began last week’s
actually starting to
talk, but I too find this stuff fascinating and as I spoke,
understand Y9
I too was reminded that “Wow! This stuff is amazing!”
chemistry – 34 years  At the age of 53 I believe – or is it hope? – that it is
late!
never too late
Still with it so far….
Great! Week 2 is the most difficult week, but people
Brilliant!
usually catch up in Week 3
17
You said…
What about
anti protons
and
positrons?
Q: What are
quarks?
I really
enjoyed the
experiments.
Michael said…
 Good question. The list of ‘stuff’ particles that I gave: protons,
neutrons and electrons, is sufficient to describe 99.99…etc% of
the universe. But there are other particles, including a class of
particles that I might call anti-stuff: anti-protons, antineutrons, and anti-electrons – also called positrons. To the best
that we have been able to measure them, anti-particles have
identical properties to their matching particle, but they have
the opposite electric charge.
 When a particle meets its anti-particle, they annihilate each
other and both particles are destroyed absolutely – and all that
is left is typically – a flash of light.
 Just to be clear about this – this is astonishing! And
investigations of why particles and anti-particles behave this
way have given great insights into the fundamental nature of all
particles and fields
 Quarks are particles even tinier than protons and neutrons and
there are a whole family of 6 of them plus their anti-particles
(see above)
 Electrons are – to the best of our knowledge – truly
fundamental particles: no matter how hard we bash them
together, we don’t see evidence of any internal structure.
 Protons are quite different. When we bash electrons against
either protons or neutrons, we see evidence of internal
structure – even tinier point like scattering centres within the
protons and neutrons: these scattering centres we call quarks.
(This is a bit like a souped-up version of Rutherford’s Gold Foil
Experiment that I mentioned somewhere later in these notes.).
Glad you enjoyed the experiments.
18
You said…
Amazing, really
funny. Has
anyone ever
travelled a light
year at one
time. See you
next week.
Michael said…
I don’t think anyone one has ever travelled anywhere near one
light year. The speed of light in a vacuum is approximately
186,000 miles per second.
 A light second is the distance light travels in one second –
which is 186,000 miles.
 A light year is the distance light travels in one year – which is
186,000 miles x 31.5 million seconds which is 5.8 million million
miles.
To travel that distance in your lifetime (say 100 years) you would
need to be constantly moving at 1/100th of the speed of light or
about 1800 miles per second. Obviously – no one has done that.
But…
The Earth itself travels around the Sun at approximately 18.5
miles per second. And the Sun orbits the centre of the Milky –
but I am not sure of the speed of that. However even taking that
into consideration I doubt any of us ever manage to travel one
light year in our lifetimes.
Excellent presentation and brilliant explanation Glad you enjoyed it: Thank you.
especially on measurement of length.
 Good reminder of  Glad you enjoyed it.
things learnt at
 Sorry we couldn’t read that word! But I am glad you
school many years
found it fascinating.
ago!
 I don’t think it is possible theoretically or practically
 A fascinating look  If we drained the electrons from your body (which
at a subject once
would be fatal ) this would make about a million
thought of in a
coulombs of electric charge.
great ??????.
 If we moved this negative charge 1 metre away from the
Very well
left over positive charge, the force of attraction would
presented.
be approximately 1022 newtons – an unimaginably large
 Theoretically
force. So I can’t really see how one would drain all of
would it be
existence of its electric charge.
possible to drain
 If we had antiparticles for the whole universe we could
or extract
completely destroy it – and the charge in it. But as far
electricity from
as we know, it is not possible to create an antiparticle
the whole universe
without simultaneously creating a partner particle.
to an alternative
one (if it exists).
19
You said…
Michael said…
 You mentioned the
 The Greeks did not ‘discover’ atoms experimentally,
Greeks knew about the
but by discussion they deduced that something like
atom. How was it
atoms (i.e. in-divisible particles from which
discovered?
everything is composed) must exist.
 What is the force that  As I think I have mentioned above, it is the strong
attracts the neutron to
force which attracts the neutrons to protons. It is
the proton? What is
a short range force – essentially a contact force –
the strong force? Does
and its origin is in the interactions between the
it exist outside
quarks that make up each proton and each neutron.
proton/neutron
 The force acts between all particles that contain
relationship?
quarks, i.e. between:
 You say everything is
o protons and protons,
electric, but you
o protons and neutrons, and
wouldn’t have atoms
o neutrons and neutrons.
without the strong
 Yes, the strong force is very important, and indeed
force holding neutrons
surprising details of the arrangements of neutrons
and protons together –
within nuclei are important in our lives – this is the
so isn’t strong force
subject of current negotiations between Iran and
equally important?
‘the West’. However, we do not in general need to
 A very enjoyable
know the details of the strong force to understand
lecture! Thank you!
the world we experience daily. Sorry for any
confusion.
 Glad you enjoyed it.
 If light gets bent around stars and  When light is bent around galaxies in
galaxies, then how do we measure
the process known as ‘gravitational
the distance of the galaxies on the
lensing’, it is usually by a very small
edge of the universe. As we are not
angle – tiny fractions of degree. So
measuring a straight line.
although its path is slightly
 I understand it’s the red shift
lengthened, this is insignificant when
which is measured, but is the red
compared with the uncertainty
shift we measure the true distance
associated with measuring the
of the galaxy and not just the line
distances to galaxies.
of light which has bent around the
 Does that make sense?
galaxies.
Balloon experiment.
Yes, if we used the Van der Graaff
- With a much larger charge, cannot generator for example we could easily move
metallic objects be moved that are
much larger objects
much larger than paper?
20
You said…
 Was the
universe
designed by an
unknown force (a
God) or do you
believe it is just
evolution that
created the
entire world?
 How do
electromagnetic
waves travel
through a
vacuum?
Why is science
so mind
boggling?
Michael said…
 Mmmm. Interesting. I don’t know.
 Over the last few hundred years many processes which
were believed to be ‘supernatural’ – for example rainbows,
or many diseases - have been understood as being
perfectly ‘natural’ processes which we can study and
analyse and modify. So if you believed these to be works
of God you find yourself in a tricky position, because
acknowledging them as being ‘natural’ means changing your
beliefs about God – something which is traditionally
fraught with difficulty. Following this line it is possible to
end up believing in a ‘God of the Gaps’ – i.e. a God which
explains all the things science hasn’t explained yet.
 Personally I don’t feel the need to invoke the idea of God
to explain things I don’t understand. I just say ”I don’t
understand”!
 We will look at electromagnetic waves (literally!) this
week. The key part to understand is that although a
vacuum by definition has no matter – no ‘stuff’ - in it, it is
not empty of fields – and these are real entities which
are always present in space.
Errr. Because the world in which we find ourselves is itself mindboggling in its beauty and complexity and size. From an
evolutionary point of view, you could say we are coping pretty well
for a group of evolved apes.
21
You said…
 Fantastic! I
feel fully
charged!
 Is this just a
graphic
representation



Michael said…
Terrible pun: well done
It is a graphic representation. We know electrons do orbit
nuclei – but atoms are so small that although we see atoms
every day – that is what you are looking at now! - we never
see this structure directly.
There is a massive space between the electrons and the
nucleus. This was deduced from one of the most famous
experiments in Physics known as Rutherford’s gold foil
experiment carried out in 1909
http://en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_experiment


Or is it what
an atom really
looks like?
It feels like
there is too
much space
between the
nucleus and
the electrons.
If you pack all
the atoms
together into
a solid, is
there still
enough room
for the
electrons to
move around?
Please explain.



Ernest Rutherford and colleagues fired the nuclei of helium
atoms (2 protons and 2 neutrons bound together and called
an ‘alpha particle) at a thin gold foil. He observed the alpha
particles by the flash of light they gave off when they hit a
fluorescent screen.
He observed that most alpha particles went straight
through the foil completely undeflected. But that
occassionaly, one or two would be deflected almost totally
through 180° and end up going back in the direction they
came from!
It was from this experiment that we deduced the basic
structure of atoms. Rutherford said
It was quite the most incredible event that has ever happened to me in my
life. It was almost as incredible as if you fired a 15-inch shell at a piece of
tissue paper and it came back and hit you. On consideration, I realized that
this scattering backward must be the result of a single collision, and when I
made calculations I saw that it was impossible to get anything of that order
of magnitude unless you took a system in which the greater part of the
mass of the atom was concentrated in a minute nucleus. It was then that I
had the idea of an atom with a minute massive centre, carrying a charge
If we cannot see
electrons and protons
how do we know the
electrons orbit the
proton?
Great question. I will explain that this week. The answer
above explains how we deduced that protons and neutrons
clumped together in the middle of an atom. We can also
deduce details of the electron orbits by looking at the
light that atoms emit.
22
You said…
Michael said…
 How do super
 This is too complicated to explain here. But briefly,
conductors work?
superconductors are materials in which – when cooled
 Do electrons
below a certain critical temperature – the electrical
actually move down
resistance of the material falls to a value
a wire?
indistinguishable from zero.
 Fire isn’t an
 Normally electrons in an electric current move through
element? Right? If
the material independently of each other 0 like millions
not, what is it made
of individuals jostling in a crowd. In the
of (the flames)?
superconducting state, the electrons move coherently
and in synchronised motion. Even though the change is
incredibly dramatic, the origin of this new mode of
motion took scientists around 50 years to work out.
 Yes, electrons do move down a wire – but not very
quickly. On average, for a typical flow of electric
current, the flow speed is just a few millimetres per
second.
 Fire – the flame that we see – is just hot gas and
unburned particles – soot.
o In ‘clean’ flames – such as from a gas burner – there
is not much soot and even though the gas is at
temperatures approaching 2000 °C, the atoms do not
give off much light.
o In sooty flames – such as a candle flame – unburned
fuel particles (carbon) glow brightly and give off
light and keep the flame temperature much lower –
but still approaching 1000 °C.
o Flames also contain a small amount of plasma – a
fourth state of matter in which atoms and molecules
are ionised.
 We discuss why hot stuff gives off light in week 3.
23
You said…
Michael said…
 Is it OK to bring
 I don’t know. If we can’t tell the difference then
another person if the
I guess it doesn’t matter.
named (child) cannot
 Yes the video was made by the Charles and Ray
make it?
Eames, who are quite interesting people for all
 Looking forward to
kinds of reasons, but who were at heart designers
showing my family the
of chairs!
video from 60s
 Good luck with the Fun Fly Sticks – I think I gave
furniture couple and
some web links somewhere above. You should be
periodic table video.
aware that the delicate floating foils are quite
 I am buying the fun fly
expensive. Perhaps you could get children to make
stick to share with
them out of the metallised-plastic foil found
pupils at my son’s
around tea bags – or similar.
schools.
 Glad you enjoyed it.
 Excellent and hands on.
 Why did you  If I did, that was unintentional. In some materials some
only rub the
directions might be a little better, but the key things are
balloon one
that the material should be dry.
way? (In one  What an excellent observation. Imagine two nuclei – lets say
direction on
they are hydrogen nuclei i.e. just single protons. When they
your shirt?)
form a molecule (H2) the two electrons make what is called a
Does create
‘co-valent’ bond i.e. they orbit both protons instead of just
a better
one. So in two-dimensions you can imagine their orbits as
charge?
being like a figure ‘8’. The key part of the orbit is the region
 What makes
in between the protons. If the electrons spend time there
2 atoms join,
then they will pull the two protons together.
if the
 If the orbits are such that the electrons are in that region
electrons
at the same time, then the electrons repel each other and
seek to avoid
the molecule falls apart – these are called anti-bonding
each other?
orbitals.
 But if the electrons orbit so that they avoid each other, then
there is very little electron-electron repulsion and the orbits
successfully bond the two atoms together
 It’s all a bit more complicated in 3-dimensions.
Terrific! Thank you.
You are welcome 
24