Download protons for breakfast march 2010 week 2

WELCOME TO
PROTONS FOR
BREAKFAST
MARCH 2010
WEEK 2: LIGHT
1
PfB12 Week 2
These are the questions & comments from Week 1 along with my responses.
For everyone’s sake, I have removed any mention of people’s names.
You said
I said
What makes
Atoms make light. We will look at this more this week in both senses of
light?
the word ’look’
Mmmm. A perfect vacuum is a region of space without any matter in it. All
Is gravity a
vacuum? Oh, and the vacuums that we create actually do contain a few atoms, but the space
can we have
in between the atoms is a perfect vacuum. Gravity is a field which exists
some cookies at
throughout space, even in places with no matter.
the break next
We had more visitors than we expected. Steve went to top up the biscuits
time? Please?
during half time. We will make sure there are more next week
Light is a disturbance of the electric field. But could
If light is a disturbance in the
electric field, could electrons and
electrons and protons also be disturbances of another
protons also be a ‘disturbance’.
field? Quite possibly, but that is just too profound a
Could they be ‘concentrations’ and
question for me to answer in this space.
‘dilutions’ of the field?
You like physics and chemistry?
I thought that the physics topic was very interesting
Great. I like atoms too.
because I like space. I also like chemistry because I
like atoms, electrons and really small things. ☺
Great Questions. But as even you know – they are
If you know how big the universe
questions without answers. Our current best estimate of
is, what’s after it? Is there an
the diameter of the ‘observable’ universe is 78 Billion
edge? I wasn’t sure about this
light years. However, the Universe it self must be much
because my Physics lessons are
larger than that, but we have no way of knowing how
really boring! But is was fun and
large.
interesting. ☺
I am glad your mind is un-boggling because I will be
I look forward to next week and
boggling again tonight!
the weeks after!
My mind is un-boggling!
It was an interesting lesson.
You are very welcome.
Thanks a lot.
The best teachers are the ones you want to
I think that is a compliment but I am not
go back to. I am looking forward to more from sure!
the Mad Scientist.
Sorry, that’s how it is. Everything we eat and drink
I don’t like the thought of drinking
is electrical in the very core of its nature.
electricity!
Yes, those are powerful sparks.
I was amazed at the holes were
I am really sorry about your not doing enough
formed by the electric sparks.
I wish they would teach it like that at experiments. Ask your teacher if he or she would
like to come along.
school. WE DON’T DO
The songs get better, and there are more each week
EXPERIMENTS!
The songs are bugging me now….. grrrr! ☺
2
You said
I said
Main question: If the nuclides in a Mmmm I can see I am going to have to give you less time
to ask questions ;-)
nucleus are held together by a
very strong short range force,
Main Answer. Firstly I think the word you mean is
why is it that this force becomes
nucleons rather nuclides. ‘Nucleon’ is a collective word
repulsive when the particles
for either a proton or a neutron because their strong
become extremely close under a
interactions are very similar. I don’t have a particular
-15
femtometer (10 m)?
answer to this question – I just don’t know. However all
forces have to behave something like this – attractive at
Stream of thought/questions: Is
‘large distances’ and repulsive in some way at ‘short
it accurate to call everything
distances’.
electrical? Everything contains
particles which would carry a
Stream of thought answer.
current if delocalised. But maybe
• Yes I think it is accurate to call everything
I am thinking of current, where
electrical. The physical properties of every
the charged particles must be
substance we encounter are dominated by the
free to move about. Perhaps that
electrical interactions between the atoms of which
is why the word static electricity
they are composed. Indeed our own bodies and
is used, as it involves localised
biochemistry are dominated by electrical
charges. This electronic field is
interactions.
also intriguing. How can something • The word ‘static’ electricity is used because the
that is not matter, interact with
electricity is not ‘flowing’ as in an electrical current.
matter, is it something to do with
• Matter interacts with the three fields I mentioned.
energy. In AS physics they talk
• Do they really talk about W-bosons in AS level
about transfer particles such as
Physics? How depressing. These are words which can
W-bosons and photons etc…..
have very little meaning in that context.
But how does this link to fields, if • I don’t think it is fair to say that ‘matter is a
a field is a different entity that
mystery’ when we know so much about it. There are
somehow affects matter, surely
of course many things we do not know. Each
there must be some kind of force
explanation of a property of matter has to be an
which in turn is supposed to have
explanation in terms of something else. At the end of
particles which are in turn matter.
a long chain of explanations there will always be a
Although it could all be due to the
few rather abstract ideas in terms of which many
fact that matter is still a mystery
many things are explained.
to us?
I am glad you and your children found it
Have thoroughly enjoyed the first week – you
enjoyable. You are very welcome.
have made science fun.
My very reluctant children had a great time and
can’t wait for the next 5 weeks. Thank you.
3
You said
• What determines
if something is +ve
or –ve charged?
e.g. why does
rubbing a balloon
always create a +ve
charge?
• How does
electricity ‘flow’?
• How many ‘fields’
are there, and how
do they interact
with each other?
e.g. is the electric
field also the
magnetic field??
I said
• The type of charge on a balloon depends on what it rubs against.
Whether electrons rub off a substance on to the balloon, or rub
off a balloon onto the substance depends on the electrical forces
attracting electrons within each material.
• In a solid the electron ‘flow’ is a series of very fast hops
between atoms. In a metal each hop takes only about 10-16
seconds, or 0.000 000 000 000 000 1 seconds. With so many
electrons hopping so quickly, ‘flow’ is a fair term.
• We know of three types of field, the gravitational field, the
electroweak field and the strong field. They do not interact with
each other at all – if they did we could work out if – or how –
they were related to one another. However many people do
believe that there is a relationship between these fields and are
searching for a GUFT – a grand unified field theory, sometimes
also called a TOE – a theory of everything.
• The relationship between the magnetic field and the electric
field fascinated people for ages – most especially Einstein who
was inspired to create his special theory of relativity by
considering the problem. I describe this relationship some way
further down these notes.
Yes. It’s called a vacuum. However there are fields
Is there such a thing as nothing?
even in that vacuum.
Just there being nothing at all and
no atoms. Plain nothing…
Are there any good I like David’s Whizzy Periodic Table
http://www.colorado.edu/physics/2000/applets/a2.html
web-sites for
understanding
atoms?
and I use web elements quite a bit
http://www.webelements.com/
4
You said
I said
• Absolutely. I don’t know why they don’t. Perhaps they could
• So, when on paper
also put a sticker saying ‘Genuine Big Bang Sourced electrons
they put “made by oak
only – guaranteed at lest 13 billion years old.
trees” or whatever,
they should put “made • I had no idea why spots come before your eyes when you are
tired. But my wife told me they are well known phenomenon.
by oak trees, and
The NHS have a page about the phenomenon.
atoms” instead. *Why
don’t they?
http://www.nhs.uk/conditions/Floaters/Pages/Introduction.aspx
• Who do dots come
before your eyes when .
your tired?
• Yes. Independent of whether the ‘source’ charge is positive
• Will static electricity
or negative, and whether the object being influenced is a
attract everything?
conductor or an insulator, the net effect is always attractive.
• I love science but I
• I have no idea how your phobia will affect you in later life. I
have blood injury
have heard it said that, whatever doesn’t actually kill you will
phobia and you have to
make you stronger. So your phobia can give you insights into
do biology as well as
how other people feel about other things. Can you think of it
as a gift that you have to figure out how to use. It’s a
physics and chemistry.
strange gift to be sure, but a gift.
We are undergoing a
• No problem
cure. Will it interfere
in later life?
• Although it is not a
very scientific
question, I hope you
will accept it.
I enjoyed getting a I have seen that film many times now and I am still amazed at just how
better perspective big the Universe is and how tiny are the things in it. And also that over
the years people have expanded their minds enough to be able to even
of how big the
universe is and how conceive of a Universe that big and particles so small. It hurts our
imagination, but people have been compelled to these ideas by trying to
small we are in
understand what they see.
relationship to it.
Atoms are very very very very very small.
That is very very very very very true.
5
You said
I said
• I am sorry: I can’t help it.
• Excellent lecture and
• Yes. It is a tremendous achievement at first sight it seems
infectious enthusiasm
impossible. In Week 2 we will see how people can work details
for your subject.
of the structure of atoms by looking at the light they emit.
• I am as mystified as
Similarly, people can work the structure of nuclei by looking
to how people can
at the gamma rays and particles that they emit. Working out
know about the
the size of the universe and the distance to stars has not
unfathomably minute
been an easy task.
inside of an atom, as
• What a profound question succinctly expressed. Knowledge is
to how people can
not a straight line progression. To be honest I don’t know
know about the far
what shape it is or how it evolves. Many people have theories
reaches of space.
about it (Thomas Kuhn and Karl Popper for example) which I
• Is the knowledge a
could only inexpertly summarise here. Occasionally people
straight-line
find that existing theories are just plain wrong – but more
progression, added to
usually they find they are limited in their area of
in building blocks? Or
applicability, and a new theory explains more, and more
do scientists
simply. It is inconceivable for example that our
continually find that
understanding of electricity and light is ‘wrong’, but it is
prior theories were
conceivable that it is in some way limited in a way we cannot
wrong. In which case,
yet comprehend.
how can you know
whether you are right?
No. Gravitational forces are not electrical, and the “strong” force
Are all the
forces electrical between protons and neutrons is not electrical.
in nature? What
Please note that in this context the word “strong” is a name for the
about gravity
forces?
force. We could have also called it the Feynman force or the Yukawa
force after some of the scientists who studied it. At short range the
force is also strong in the normal sense of the word
Excellent. We all need a reminder from time to time.
Tonight has
They didn’t. It’s a fantasy – and put together in the crudest way – a series
reminded me
of 40 pictures were created and then a camera was moved away from the
why I like
picture to create the zoom effect. However the boldness and clarity of
science. Thank
the conception, and the focus on conveying a simple truth are still very
you!
powerful. The film has many shortcomings – for example at some point not
How did the
guys making the too far from Earth, the viewpoint apparently recedes faster than the
speed of light – something which is physically impossible. An earlier version
film know what
attempted to communicate this, but in the end they just ignored this
the view looked
complexity. Sometimes, saying less communicates more ☺
like so far out
from Earth and
our universe?
6
You said
I said
• Excellent
• What a great
lecture. There was • Mmmm. Well it is important and it isn’t. No one will live or die as a
result of any discoveries at the LHC whether they discover the
a lot I understood
Higgs boson or they don’t. But on the other hand it represents
for the first time.
one frontier of knowledge and understanding – the largest
• Why is the
scientific instrument ever constructed – and just a totally mindmeasurement of
bending achievement. You should decide how important it is: after
small things like
Hicks (Higgs)
all, you’re paying for it!
particles so
• The distinction between stuff and not stuff (which are not
important?
technical words by the way) is maintained even when things get
• Do very big and
very small. But very small entities do not obey Newton’s of
very small things
Motion; they obey another set of rules called ‘Quantum
act differently or
Mechanics’.
do they all still
• There are other basics too: but at the end of the 19th Century
behave as stuff
scientists thought they understood it all apart from a few
and not stuff?
‘details’. I have emphasised the electrical nature of things
• Is the basis of all
because (a) it is true and you can immediately appreciate that; (b)
physics electricity
it is just not mentioned in current text books. But don’t get me
or are there some
started on text books!; and (c) understanding the electrical
other basics too?
nature of matter has huge explanatory power.
That was also a periodic table. There is more than one way to reflect the
What was the
periodicity of the elements and I like that structure because its spiral
table with
elements on that structure reflects the ‘stacking’ of ‘shells’ of electrons.
was next to the
periodic table?
I love them too ☺
Fun fly sticks.
As I said above, there are lots of alternative ways of reflecting the
Didn’t understand
periodicity of the elements.
the round Periodic
Great
table.
Loved it though.
Do electric (and magnetic
Yes. They react at exactly the speed of light
fields) react at the speed
of light?
Why do merchant bankers Advanced theoretical physics is hard but I can do that. Figuring
out why bankers get bonuses and knighthoods is beyond me.
get knighted as a matter
Regarding my MBE, I feel I should be more cynical and sceptical,
of course and you got a
but actually I just feel delighted, and profoundly honoured.
MBE? Surely should be
the reverse!
7
You said
What are
electrical
charges like for
antimatter?
What exactly is
the Heisenberg
uncertainty
principle?
I said
Short questions with big answers.
• Electrical charges for antimatter particles are the opposite of the
charge for the equivalent matter particles. So an electron with a
negative charge has an antimatter counterpart called a positron which
has positive charge of equal magnitude. The electrical charge on a
positron is exactly equal to the electrical charge on a proton
• Small objects do not obey the same laws of motion as large objects.
Their dynamics are described by the laws known collectively as
‘Quantum Mechanics’. One aspect of these laws is that it is not possible
even in principle to know everything about a particle. For example, we
might carry out an experiment to workout how fast an electron is
travelling, but the more precisely we determine its velocity, the less
precisely we know exactly where it is! The limit of the least
conceivable uncertainty of measurement we can have on simultaneous
measurements of position and velocity was calculated by Werner von
Heisenberg.
• Does that make any sense? I hope so.
• I think you mean a ‘field free’ region
• Can you make a “vacuum” of a field, i.e. a
analogous to a ‘particle free region.
enclosed space that has very little or none of
Well it is possible to create regions
the gravitational field or any other field. I’m
where an electrical field is zero on
guessing the simple answer is no, but why?
average, but it is not absent! If you
Supposing you could, what implications would
could screen gravity then we could
this have.
have flying machines!
• What if my favourite radio station is a DAB
station!?
• Even DAB has a frequency, but not
• You should have the “This page is intentionally
all radios display the frequency.
left blank” paradox, get rid of the “aside from
• Your wish….
this writing” bit (it’s funnier that way).
• Ha Ha …
• There are 10 types of people in the world.
Those who understand binary and those who
don’t.
Errr….Thank you. I think?
This was more
interestingly quirky that Vector diagrams are quite tricky. But if you practice they do make
sense. Do you have a particular problem or is just vector diagrams
I thought it would be.
in general?
Question: Why are
vector diagrams so hard A diode in general terms is any component with two leads. ‘ode’ is
the Greek for a ‘way’. So di-ode is ‘two ways’. The thing that
to figure out and
distinguishes a diode from a resistor is that its electrical
calculate in my mock
resistance is different depending on which way it is connected in a
exams?
What is a diode and is it circuit. Electrons flow easily one way, but barely flow at all in the
reverse direction.
bad that I still don’t
Is it bad you still don’t know? Don’t worry about it – everyone has
know?
big holes in their knowledge. Just learn and move on.
8
You said
Good revision
for me, very
simple, easy to
understand
explanation. The
introduction was
a bit long, would
have been more
interesting to
learn more about
electricity.
• Can you try
and explain
dipoles? We
did it in
chemistry but
I was a bit
stuck.
• What is
fire?
I said
I am glad you found it simple. Yes, the introduction is a bit long, but we
will use these ideas over and over again in the coming weeks.
• We will talk about dipoles – but I won’t really use the word explicitly.
Why? Because it gets technical quite quickly.
• Some molecules – such as water – have a built-in (or permanent) dipole
moment. The exact reasons for how this comes about depends on the
particular arrangement of electrons around the molecule. This affects
the way the molecules move in an electric field, either applied by us or
due to other molecules. For example below is a schematic illustration
of a water molecule. When another water molecule approaches, it will
feel forces that attract its positive parts to the negative parts of the
first molecule. Many of the special properties of water arise from
exactly this effect.
Some molecules don’t have a built in dipole moment but can be
polarised by an electric field either applied by us, or due to other
molecules. If you imagine a spherical atom, then when an electric field
is applied the electrons move slightly one way, and the nucleus moves
the other way. So the centre of the positive charge and the centre of
the negative charge are not in the same place: the atom has acquired a
dipole moment. That was the process I tried to describe by which the
piece of paper get picked up.
• Fire is simply hot gas, sometimes with small particles of soot. In some
parts of the gas the temperature is so high that atoms and molecules
become ionised. In those regions the gas is technically known as a
plasma. You can tell exactly the type of atoms and molecules in the
flame by looking at the light it emits – more on that in the weeks 2 & 3
Wow! Well done. It gets very hard to return to formal
Very please I have understood!
studying in later life.
It was worth doing a science
Amazing – but true! I don’t know why people don’t
GCSE at 52 last year!
I had not really appreciated that emphasise this more.
You are welcome.
everything was affected by
electricity before tonight.
Thanks.
•
9
You said
I said
Yay Physics indeed.
Yay, physics ☺ Good
• By the ‘other side’ do you mean the ‘inside’? I think you do. Well
A-level revision.
the answer is that no one knows. The concept of a black hole
Could you answer
involves the concept of a singularity – a point of infinite density.
these?
In physics there are no known examples of infinite quantities.
- What is on the
The Physics in this kind of region is beyond anything we really
other side of a black
understand.
hole?
• I don’t understand that question
- What happens if 2
black holes face each • See above. And listen out in the following weeks.
• Is it a liquid? I had not thought of it as so. I had thought of it as
other?
a dense plasma, but maybe a liquid is a good way to think of it.
- What IS fire? (my
Looking it up on the web’ the density in the outer part of the sun
dad’s a fireman and he
is roughly the same as liquid water, but the density of the inner
can’t answer this well)
part of the sun rises to 1000 times that of water – at a
- Why is the inside of
temperature of roughly 10 Million degrees celsius.
the sun a liquid?
• I don’t think there is a definite experimental answer for the
(rather than a solid).
shape of space-time.
- What shape is space
• A wormhole is an imaginary structure in space-time that somehow
– is it a saddle or a
connects one point in a universe with another point which is
donut?
apparently very distant in space and/or time. There is no
Thanks ☺
evidence that any such structures exist or can exist. But it is not
*Also (1 more) – What
wholly inconceivable.
is a wormhole?
It is called Powers of 10. You can see it on You Tube as
What is the video about
the zooming in and out
called because I would
http://www.youtube.com/watch?v=A2cmlhfdxuY
like to use it?
If there are 70 beats of I am afraid it is only my supposition that the second is roughly
a heart per minute then
related to a heartbeat. But our heartbeat is our constant
why are there only 60
companion and it seems plausible.
seconds in a minute.
It is indeed true, and the humidity of nearly 100 bodies in the
That means a heartbeat
lecture theatre caused the one I had to stop working. But when
isn’t based upon a
people went out for the break, the air conditioning managed to
second. My science
catch up and the experiment worked after the break. (Following
teacher said that van de on from an answer above, I think the reason water is so effective
Graaf generators work
at conducting electricity in the air is because it has a permanent
badly when it’s wet
electric dipole moment)
outside. Is it true?
I am glad you like it. I think it gets better as we go on!
The course is very, very
good!
10
You said
Are the electrons free
on your jumper? from
the outside of atoms of
jumper.
When did the electrons
come vis a vis the Big
Bang.
Don’t the atoms in the
air affect the field?
I said
No, not free – they are attached to atoms in my jumper. When the
balloon touched my jumper, electrons right at the surface were
pulled onto the balloon or the pullover depending on the electric
forces in each material.
Electrons were created along with protons in the first second or
so after the big bang. I find that amazing all the electrons in my
body are not merely 50 years old – but 13 billion years old! – no
wonder I feel so tired all the time ☺
Yes, they do. But not very much. Except if they have a dipole
moment (such as water) in which case they conduct electricity a
bit more than dry air.
Yes. Whether electrons are rubbed off an object or onto it depends on
the electrical forces on the electrons near the surface. These vary
depending on the detailed arrangement of atoms. The effect is known as
the triboelectric effect and materials can be ranked in a series, called
the triboelectric series. The series is very approximate, but allows you to
figure out which way the electrons are moving when you rub any two
materials. Read more here:
If you rubbed
the balloon (or
something else)
on something
other than your
jumper would it
add (take away) a
different charge
to the outside of
the balloon (or
other object)?
Is enthusiasm electric?
Thanks for a very
enjoyable evening.
Origin of the Universe. I
personally believe possible
that the Big Bang theory
as the start of everything
has to be wrong.
The explanation for the
Big Bang surely is that
matter gets attracted to
Black Holes. Black Holes
get absorbed into other
black holes. Gravity gets
stronger and stronger at
some point the forces
become unstable and a
large explosion occurs.
Where could I find out
more about black holes
and the big bang?
http://en.wikipedia.org/wiki/Triboelectric_effect
Errrr. I’m not sure. But possibly….
You are very welcome.
Mmmm. Well that’s an interesting theory, but where is your
evidence? The theory of the ‘big bang’ is constructed to match
our observations. People have considered the question you have
asked, but the question is “How could one tell?”. So they have
asked questions like, if there was a universe before the big bang
that was first crushed and then exploded, could we tell by
looking for evidence in the world around us?” Currently the
answer is ‘not really’
NASA has some nice sites
http://nasascience.nasa.gov/astrophysics/what-powered-thebig-bang
http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.
html
For details try Wikipedia, but it is a bit advanced.
11
You said
Why can’t atoms
be enlarged so
we can find out
about them?
They built a
Hadron Collider
so what’s
stopping them?
I said
Atoms have a natural size which depends on the strength of the electric
field around protons and the properties of electrons, particularly their low
mass.
People do take great interest in studying what are called Rydberg atoms,
which are hydrogen atoms where the electron orbits the nucleus at a great
distance – many times its usual orbit radius.
Building the LHC is a stupendous engineering achievement. But changing
the basic properties of matter is something which is beyond even our most
advanced engineering.
• Nobody knows. It seems likely but…nobody
• Universe so large. Are there other
really knows.
life forms out there?
• We will look at this in Week 5 – because that is
• If the balloon/electricity affects
the basis of the potential hazard arising from
the “sausage”, how does the
mobile phones.
electric/radio waves affect us?
• You are welcome
• Great and enthusiastic speaker.
• Yes, it is hard to avoid this concept of entire
Thank you.
universes within universes.
• It seems that we are in the
Universe and even the chaps hand
(our bodies) are a micro universe.
• Atoms are indeed made out of electrical ‘bits’
• Are atoms made entirely of
(particles). The ‘solidity’ arises entirely from electrical
electrical “bits” which
forces between atoms.
appear as solid matter – i.e.
• I am afraid I am not going to explain the big bang – I
is matter made entirely of
can’t, but then neither can anyone else! As I mentioned
electrical charges.
above, it just appears to have occurred around 13 billion
• Are you going to explain
years ago.
“the big bang” i.e. where did
it come from?
Electric thought.
I am afraid I can’t quite follow that: maybe that is just what was on
Glass for rear lights
your mind.
etc.
I wasn’t aware quite how much electricity there really is
Excellent. Most people are not
and how significant it is in our every day lives!!!
aware of that.
I thought that it was excellent. I
I am glad you enjoyed it. Thank you.
liked the way it was presented.
I am glad you enjoyed it. Yes, the Sun has loads of electrons. The mass of
I really enjoyed
the Sun is around 2 x 1030 kg. Most of this is hydrogen and a hydrogen
this and learnt
loads of facts.
atom has a mass of roughly 1.6 x 10-27 kg, so there are roughly 1.2 x 1050
Does the sun
hydrogen atoms – and so there are roughly 1.2 x 1050 electrons. That is a
have electrons?
really really big number!
12
You said
I have? a lot of static
electricity/charge – why
is that?
To date, I have blown up 6
toasters! 4 kettles! 1 iron
and literally 100s of bulbs.
It is also worse in summer
– why?
If I wear cottons clothes
it does decrease and avoid
polyester/nylon. Why
does cotton have less or
no static?
I get loads of zaps from
my car, earthing strips
don’t work – what can I
do? Please help.
I said
• Well firstly I don’t know. But the humidity of the air strongly
affects the conductivity of the air. When the air is humid,
triboelectric charges (i.e. charges separated by rubbing) leak
away back to where they came form much more quickly than
when the air is dry. So if it is worse in summer (when the air
is generally drier) then the charges probably arise in this
way.
• No insulator is perfect, they all conduct electricity a little.
Cotton conducts electricity much better than man made
fibres, and also holds moisture longer enhancing the
conductivity of nearby air.
• Think about walking barefoot and avoiding carpets made with
man-made fibres. Are your floors concrete or wood? Do you
have good air flow? You could always try ionisers which
reduce static build up.
• Cars acquire a static charge because they have rubber tyres
rubbing against insulating asphalt when they drive.
I enjoyed the talk. I learnt many things on
I am glad you enjoyed it.
atoms and the sizes of the planet.
• I don’t know what a gravity vortex is. I am not sure that such
• What about a gravity
a thing could exist.
vortex?
• Stuff and Non-stuff: YES!
• Stuff (particles), Not
• What a great question. This was amongst the toughest
stuff (non particles).
unanswered questions at the start of the 20th Century.
• What stops the
negative (in an atom)
Eventually people realised that tiny particles do not obey
going straight to the
Newton’s laws of motion – called classical mechanics – like
positive in the middle
large particles do.. If they did every atom would instantly
instead of orbiting?
collapse as you suggest. Small particles obey rules called
• With atoms, if you
Quantum Mechanics.
touch someone how
• Well you do stick, just not very strongly. If two electrically
come you do not stick
neutral objects are brought close to each other (by close I
to him/her?
mean 1 nanometre), there is a weak attractive force between
• What about wind?
them, but this turns to repulsion when they reach a
separation of around 0.1 nanometre.
• Pardon me ☺
1. All the physics that takes place on length scales ranging from the
1. How many
diameter of the solar system to the size of an atom can be explained
dimensions.
assuming there are exactly three dimensions of space and one dimension
2. How many
of time. If there were any more or less, we could tell experimentally.
black holes.
2. I don’t know of even a single black hole that has been unambiguously
identified, but there are many many candidate objects.
I really enjoyed this class. Excellent.
13
You said
I said
You have been before? One key element of learning is
I understood this more
familiarity. Sometimes it just takes a little while for ideas to
the second time of
first become familiar, and then when they are familiar, they
visiting.
begin to make sense. One problem with learning is that it is often
I now understand how
hard to become familiar with new things – one tends to avoid
absolutely everything is
thinking about things which we don’t understand.
electrical.
If you understand that everything is electrical then you have a
Hopefully a few topics at
profound insight into the world.
school will make sense
I hope so☺
now!
Excellent.
I have learnt that
I am glad you are not confused about the size of the universe.
everything is electrical.
Not so confused about the But confused or not, its hard not to be at least a little boggled!!
size of the Universe.
• Yes.
Can sand get
• At first I thought you were asking whether things could be lifted by the
lifted by a
buoyancy of the balloon, which case the answer is this: A helium balloon
balloon?
with a volume of one cubic metre has a diameter of roughly 1.3 metres
Can we lift
and (neglecting the weight of the balloon itself) can lift about 1 kg of
our own food.
sand (about half a litre of sand).
• But when my wife read this she said she thought it was a question about
whether a balloon could lift a particular weight electrostatically. The
answer is still yes, but the weight that can be lifted depends on how much
electrical charge there is on the balloon. But with enough charges, you
could lift anything.
Its tricky. Early measurements made by a scientist called Michelson worked
How do you
like this. A bright light was shone onto a rapidly rotating mirror onto a
measure the
distant mirror – perhaps one kilometre away. The light was reflected back to
speed of
the rotating mirror. The round trip takes roughly 7 microsconds. If the
light?
How accurate mirror rotates 100 times per second, then it will have rotated roughly one
quarter of a degree when the light returns and the image of the light will
can you
appear in a different place. By measuring the distance the light travelled and
measure a
knowing the speed of rotation of the mirror, the speed of light can be
metre to?
measured by measuring the deflection of the image. Nowadays we don’t
measure the speed of the light – we define it to be a constant and use it to
work out distances and times.
We can pretty easily measure one metre to 0.000 1 millimetres. More
accurate than that gets a bit tougher.
14
You said
How did
scientists
discover that
there were
fields i.e. that
the world is
not just
matter?
I said
Great Question. Ignoring gravity for the moment, people spent a great deal
of time trying to understand the nature of electricity and magnetism, and
quite separately, of light. There were many nascent attempts to imagine how
magnetic and electric phenomena affected distant objects. But in the middle
of the nineteenth century, all the pieces came together. It was a combination
of new experimental results and new mathematical techniques that made it
possible.
James Clerk Maxwell was trying to understand how electric forces (like
those from the balloon) were communicated across space. He constructed a
theory which posited that something existed in the space in the absence of
matter (they called it æther). He worked out what speed waves in this ‘field’
would have and found – to his astonishment – that the speed was exactly the
same (within a very small uncertainty) as the measured speed of light. In his
journal he wrote that this ‘could not be a coincidence’. This was the first
modern field theory and it was essentially perfectly constructed at the
outset. About 50 years ago Richard Feynman modified the theory to explain
how light waves are emitted and absorbed in finite ‘chunks’ known as photons.
Can you crush a Yes. But we can’t exert such strong forces on Earth. In certain stars known
as neutron stars, the gravitational field is so strong that atoms are crushed
atom?
and the electrons are squeezed into the nucleus and – using physics that is
Could a wave
way beyond this course or frankly me personally – the electrons combine
affect the
with the protons to make neutrons. And the stars consist of pure neutron
earth or the
matter, roughly one million million times denser than any substance on
earth’s
Earth.
atmosphere/
Yes. Waves of all kinds affect us all the time. We will look at some of this
in Week 4.
When can I meet the elderly, presumably Oh. Sorry we have other Robert Goddard helping
retired, white haired rocket scientist you
have helping out as a helper?
http://en.wikipedia.org/wiki/Robert_H._Goddard
Your “helpers” slide showed Robert
Goddard as a helper.
There is a lot of it about, but separating it from matter to
I didn’t realise there was so
make useful electrical power is still quite a trick.
much electricity hanging about
You are welcome
– I thought we had to do more
to make it!
Thanks a lot.
Excellent.
Very
It depends on the type of light bulb. In the simplest type of light bulb,
interesting!
there is a filament (a thin wire) of tungsten – an element which does not
Q. How is
melt until 3422 °C. An electric current flows through the wire and heats it
electric
to an astounding 2500 °C! At this temperature, the light bulb gives out lots
converted to
of electric waves, some of which are visible – light! We will talk more about
light in a bulb?
how this comes about tonight and again in Week 3.
15
You said
How do atoms of
the same type
(e.g. H) ‘attract’
each other to
form molecules
when they both
have – charges on
the outside.
I said
Great question. The atoms may be neutral, but the electrons are not
uniformly arranged around the outside of the atom. Atoms in which the
electrons are uniformly arranged the outside of the atom (Helium, Neon,
Argon, Krypton, Xenon and Radon) do not form multi-atom molecules, and
indeed barely react chemically with anything else.
On other atoms the electrons are not uniformly arranged around the
nucleus. That means that other similar atoms can ‘see’ the charge on the
nucleus. For the person who asked earlier – the atoms form an
instantaneous electric dipole. And this can electrically attract other
atoms or molecules.
The electron was ‘discovered’ by J J Thomson. People had investigated
Who discovered
electrical charge the ‘rays ‘ that could be drawn from a negatively charged piece of metal
called a cathode in side a glass tube which had most of the air removed.
of Protons and
The devices were called cathode ray tubes. Thomson performed a series
electrons and
of experiments that showed that the rays were streams of
how?
extraordinarily light particles with a negative charge.
The story of the discovery of the proton is more complex, but the key
figure was probably Ernest Rutherford. You can read more on Wikipedia
here:
http://en.wikipedia.org/wiki/Proton#History
I don’t know if the Universe goes on for ever. And although
Does the universe go on
there is much speculation on the matter, I don’t think there is a
forever? Because
otherwise if it ended what really definitive scientific view on the matter.
would be outside it?
Yes! Atoms in the air and within our body are
Are we not affected by the
constantly jiggling. If the jiggling gets too intense (i.e.
constant pull and push of atoms
if the air or our bodies become too hot) then we indeed
around us.
cannot cope! More in Week 3
How does our body cope with this?
It was very fun but maybe we could have maybe 15 Mmmm. It’s a balance. In week 2 you
mins more time to use all of the amazing
have 5 more minutes! And Week 3 is a
experiments?
bit more relaxing.
But I really enjoyed it and learnt a lot and also
I am glad you enjoyed it.
thought he was very good at what he did. Thnx.
Excellent. Yes it can be disconcerting
I was fun and interesting and I learnt a lot.
sometimes to think about just how small
I liked watching the experiments. It made me
some of the things in the world are, and
realise how small everything in the world is.
a just how big is the Universe in which
It helped me understand a lot more of what I
we live.
know.
You are welcome.
I enjoyed the videos.
Thanks.
Time travel – how could it
Aside from my regular trawl through time, I know of no way of
be done?
travelling through time.
16
You said
I said
Why are Bourbons more attractive Chocolate. We will try and have more next week.
You are welcome
than Digestives?
Thanks.
The Greeks could not see atoms (except in the same way that we all see
How could the
atoms all the time). Sometime around 450 BC Democritus reasoned that if
Greeks see
atoms to know
one kept dividing a substance into a smaller and smaller parts one would
that they
eventually arrive at a particle which could not be cut (literally an a-tom).
couldn’t be cut? In this original conception, stones would be made of atoms of stone and
fur would be made of atoms of fur. The idea was that these atoms were
indestructible and merely recombined to make new substances. So some of
the key ideas of our modern concept of atoms were there, but also several
key concepts were missing. The reasoning at this time was speculative –
our modern conception of the atom is very much based on factual evidence.
You are very welcome. I am sorry to hear
My Feedback:
that your Friday lessons are
I’m in year 8, and I’ve learnt more HERE than in
disappointing, but glad you enjoyed the
my Friday lessons!
I learn in my Tuesday lessons, but not so much on session.
Well you can test the pencil! Hang it up
my Friday one! This has really helped. Thank you
by a thread tied around its middle and
very much.
Everything is electric? REALLY. Even this pencil? see if you can attract it with a balloon!
Yes, the atoms and molecules in the air are affected,
How does the charge on the
but only weakly. In each cubic centimetre of air there
balloon induce the charge on the
are roughly speaking only one thousandth of the number
paper through the air i.e. how do
of atoms and molecules as in 1 cubic centimetre of any
the atoms in the air between get
solid or liquid substance.
affected – is a charge induced in
the atoms in the air as well?
Why does it make a Whether electrons are rubbed off a material onto a balloon, or off the
balloon onto the material depends on how strong the electrons are
difference what
sort of material you attracted to the atoms of the rubber and the other material. This
depends all kinds of complicated details of each substance. The
rub the balloon on
i.e. cotton, wool, etc. roughness of the surface will also make a small difference. There is a
reasonably well documented series called the triboelectric series
Does the surface
make a difference
which says which things rub electrons off which. The list si below, for
i.e. smooth, rough,
what its worth.
knitted, woven.
http://www.siliconfareast.com/tribo_series.htm
17
You said
You mentioned
Fields
- Gravitational
- Electroweak
- Strong.
Not heard of
them before,
what are they?
Heard of
electromagnetic
.
I said
Protons affect other protons through all three fields. If a proton moves
then:
• The gravitational field is disturbed because protons have mass. A
short while later when the disturbance reaches other protons they will
move in response.
• The strong field is disturbed because protons have another property
about which I have not told you (!). The disturbance doesn’t travel far
in the strong field. A short while later when the disturbance reaches
other protons they will move in response. Because the disturbance
doesn’t travel far, protons only affect other protons through the
strong force when they are very close.
• The electroweak field is disturbed because protons have electrical
AND
charge. A short while later when the disturbance reaches other
protons they will move in response.
What is an
We have described the electrical aspect of the electroweak field.
electroweak and However there are also a ‘magnetic’ and a ‘weak’ aspect. We can see the
a strong field?
connection between electricity and magnetism fairly easily. (ish)
• When an electrically charged particle affects another electrically
charged particle through the electroweak field we call the interaction
electrical.
• If the either particle is moving we still describe the interaction as
electrical.
• However if both electrically charged particles are moving (e.g. in two
wires), we describe the interaction as having an additional magnetic
component. However, if we imagine travelling with one of the charged
particles, then it would appear stationary, and we would then have
describe the interaction as purely electrical. Considerations such as
this led Einstein to formulate his Special Theory of Relativity which
allowed us to understand that magnetic interactions are really just
‘How electrical interactions look when charged particles are moving’.
The ‘weak’ interaction is more complicated to describe, and if you will
forgive, I will not do it here. Again the word ‘weak’ is just a label
describing a short-range interaction between particles which is not the
‘strong’ interaction. The connection between the electromagnetic and the
weak force was only discovered in the 1980’s.
By this question I assume you mean Einstein’s General Theory of
Do you understand
relativity. If you do then the answer is indeed ‘No.’ I suspect the
gravity? My brother
answer is many more than 10 – nearer 1000 or so, but indeed that is
said only about 10
still not a large number.
people do?
18
You said
In outer space
is the majority
of space
matter or a
field?
I said
In outer space there is only a single atom (usually hydrogen) in each cubic
centimetre of space. So the most of the space is filled with ‘fields’ rather
than matter. In contrast, in the air around you now there are roughly 1019
atoms in each cubic centimetre. 1019 is
10 000 000 000 000 000 000 atoms. –ish.
I’m finding the course very informative
We have lots, lots more to show and tell. And
and can’t wait to learn more!
more songs too ☺
• Its something else! Electric charges don’t affect the strong field.
• What was
However some particles such as protons and neutrons have other
the
properties (which I haven’t really discussed) which do affect the strong
difference
field. Thus when a proton moves it disturbs not just the electric field,
between
but also the strong field and the gravitational field. Although protons
electric
repel each other electrically, they attract each other through the
fields and
strong field. However unlike the disturbance to the electric field which
‘strong’
extends for a long distance through space, each proton only disturbs the
field – if
strong field for a very tiny distance around itself. This makes the
strong isn’t
electric –
strong interaction between protons essentially a contact force. The
what is it?
strong force acts roughly equally between protons and neutrons – it just
• How can we
doesn’t ‘see; the electric charge the particles possess.
measure
• Measuring the distances to planets and stars and galaxies is very
space? (per
difficult and it is a triumph that we can do it at all, even though there
the film?)
still uncertainties involved in our estimates. For relatively nearby stars,
• Thank you.
we can work out how far away they are by looking at them against the
background of more distant stars at different points on the Earth’s
orbit around the Sun. We can detect tiny differences in the apparent
position of the stars and knowing the diameter of the Earth’s orbit we
can work out the distance to the stars.
http://heasarc.gsfc.nasa.gov/docs/cosmic/nearest_star_info.html
There are other tricks for finding distances to more remote stars. We
have studied nearby stars called Cepheid variables. The absolute
brightness of these stars varies every few days, and the period of the
variation is longer for brighter stars. If we spot such a star in a distance
galaxy we can measure its period, and infer how absolutely bright the
star is. By measuring its apparent brightness we can work out how far
away the star is.
http://starchild.gsfc.nasa.gov/docs/StarChild/shadow/cepheids.html
I told you it was complicated!
• You are welcome
19
You said
I said
To the best of our knowledge all protons have exactly the same value of
Do all protons
have the same
electric charge. They have also checked that electrons have exactly the
level of
opposite value of electric charge. People have checked this very carefully.
electricity?
As I think I mentioned somewhere above. When the
You touched on role of valence
electrons in chemical reactions. electrons orbiting an atom make a perfectly spherical
Example given was two H atoms pattern around the nucleus then the atom is chemically unreactive. This is called ‘completing a shell’ by chemists. In
combining to give H2 molecule.
other atoms, the outer (valence) electron shell is not
But if electrons have same
complete – that means that the other atoms can detect
charge you might think they’d
some of the electric charge on the nucleus and are
repel. Does this mean that the
valence electrons are important attracted to the atom. Once the atoms get very close the
electrical forces become very strong, and coupled with the
for some reason, but that the
unusual dynamics of small objects (called Quantum
full story must involve the
mechanics) the electrons adopt new orbits in what is called
protons also? Any insight into
a ‘chemical bond’
why valence electrons are so
chemically important?
It is a very confusing term. In a sense every chemical reaction ‘splits’ atoms
What does
because takes or adds electrons away from atoms. However the phrase
splitting the
would be more correct if we spoke of splitting the nucleus of atom.
atom mean?
This can be done in a number of ways, but typically, it involves bombarding a
substance with protons or neutrons or even entire nuclei of other atoms.
Most of the particles don’t hit nuclei in the target but some do, and by
interact electrically and through the strong force they can break up a
nucleus.
Technologically the most important case is the fission (the scientific word
for splitting) of some atoms of Uranium. Addition of a single neutron causes
the entire nucleus to split into two or more parts. The fragments move
enormously fast and release tremendous amounts of energy. The process is
at the heart of both nuclear power and nuclear weapons and we will look at it
more in Week 6.
20