## ODU Resources

Well after spending 18 months or more several years ago putting everything together students have unanimously declared they want everything separated, so your wish is my command students- here is the complete Our Dynamic Universe section notes with nothing but the essential practicals plus one!

These need a real sort out and I’ll get on to it as soon as I can. I’ll upload lots of resources that are now hard to find. I hope they’re useful to teachers and students.

# 2018-updated

These are part 1 of the notes in pdf format, so you all ought to be able to open them. There is a word version underneath.

These are part 1 of the notes in word format, you can adapt these if you can open them.

For those having trouble with Unit 1 part 1 try this little document

1. 1a Equations of motion

Part 2 still has to be updated to be 2018 ready.

These are part 2 of the notes in word format, you can adapt these if you can open them.

OUR DYNAMIC UNIVERSE part 2 These are part 2 of the notes in pdf format, so you all ought to be able to open them.

I’ve removed the Time Dilation detailed version and added it as a separate document as I suspect most of you wont read them; which is a pity as it makes everything seem fine! Based on Russell Stannard’s excellent book “Relativity- a very short introduction” Oxford. (2008)  ISBN 978–0–19–923622–0)

ODU worked ANSWERS_4 Currently the most up to date version of the worked answers.

For those struggling with the vectors try these to give you some practice Great Resource from Mr Crookes. Set up your 2 vectors, either use a scale diagram or components and compare to the given answer. Enjoy!

AH (Doppler)– some of this is relevant to Higher.

africanfastfood This is an introduction to the momentum topic; think about the collision and where the energy is transferred.

4.4 ODU EqoM 2012 this document has the macros enabled. It allows you to check your answers for the acceleration time graphs that you drew from the velocity time graph diagrams.

If you don’t like proving v2=u2+2as from v=u+at then use this neat little sheet from Mr Mackenzie.

using displacement equation to prove the last equation

### Relativity

The green dots and red dots in the animation represent spaceships. The ships of the green fleet have no velocity relative to each other, so for the clocks onboard of the individual ships, the same amount of time elapses relative to each other, and they can set up a procedure to maintain a synchronized standard fleet time. The ships of the “red fleet” are moving with a velocity of 0.866 of the speed of light with respect to the green fleet.

The blue dots represent pulses of light. One cycle of light-pulses between two green ships takes two seconds of “green time”, one second for each leg.

As seen from the perspective of the reds, the transit time of the light pulses they exchange among each other is one second of “red time” for each leg. As seen from the perspective of the greens, the red ships’ cycle of exchanging light pulses travels a diagonal path that is two light-seconds long. (As seen from the green perspective the reds travel 1.73 ({\displaystyle {\sqrt {3}}}) light-seconds of distance for every two seconds of green time.)The animation cycles between the green perspective and the red perspective, to emphasize the symmetry.

OnVelocities This is a document referred to in the Research Task in the ODU part 2 notes.

PHYSICS WORLD ARTICLE DECEMBER 2009 This is a document referred to in the Research Task in ODU part 2 notes

Projectiles thanks to Mr. Rossi for this one.

Battleships & AWACS Projectiles thanks to Mr. Rossi for this one too.

Chapter 1 exam questions B for CFE higher

Chapter 1 exam Answers B for CFE higher

##### The Expanding Universe

Are we missing something in the Expanding Universe?

# HOMEWORK

The homework booklets are now in the HOMEWORK section.

Homework Booklet Complete pp6-8 (first question), 10-16, 18. Complete notes on Units prefixes and Sci Notation, Uncertainties, Equations of Motion. Read up on Forces.

## Higher Prelim

Topics for the Prelim: Our Dynamic Universe, Part 1 of Particles and Waves, Uncertainties, two open ended questions

Hi Folks these are the dates for the Higher Prelims

Mrs H’s class: Thursday 11th January P2, multiple choice questions

Friday 12th January P1 & 2 extended questions

## What is the Biggest Ever Redshift?

A discussion on the Physics Teachers’ Network requested advice on “What is the biggest ever redshift detected?”

Research shows it was a redshift, z = 11.09 for galaxy GN-z11; and the measurements were  taken in the near infra red using Hubble’s Wide Field Camera.

This is a big question because effectively we are seeing the furthest galaxy back in time.  It is 32.2 billion years away and came into existence 400 million years after big bang.  So if the Universe is only 13.8 billion years old then how come we can see something so far away?

During this time the Universe was opaque and full of neutral atoms.

Professor Martin Hendry supplied an interesting reply.

In some cases we can determine the redshift of a galaxy by measuring the wavelength of a particular spectral line that corresponds to a particular transition of an electron in a hydrogen atom.  For example the Lyman alpha emission line is the result of an electron dropping down from the n=2 energy level to the n=1 energy level, and the presence of this spectral line is often seen as an indicator of a recent burst of new stars forming as one might expect to see in a very young, recently formed galaxy.  (This line was proposed as a tell-tale sign of a very young galaxy by Bruce Partridge and Jim Peebles – awarded the Nobel Prize for physics this week: see e.g. https://en.wikipedia.org/wiki/Lyman-alpha_emitter).  This line has a wavelength of 121.567 nm in the rest frame of the hydrogen atom.  If a galaxy is a strong Lyman alpha emitter, and the line is observed at wavelength lambda, then by comparing the observed wavelength with the 121nm at which it was emitted we can measure the redshift of the galaxy.

(Of course if this spectral line is redshifted then how do you know it’s a Lyman alpha line?  Likewise for any other spectral line.  Often it’s the combination of several spectral lines and their relative spacing that gives the game away – a bit like a bar code in the supermarket.  You could imagine enlarging the image of a bar code in a photocopied and, generally, it’d still be recognisable as the overall pattern would still be the giveaway).

In fact for this record-holding galaxy, the redshift was determined a slightly different way, from the Lyman series but not the Lyman alpha line and not from an emission line but an *absorption* line: specifically it was determined from the “Lyman break” – i.e. the limiting wavelength that corresponds to the amount of photon energy you need to absorb to allow an electron in the n=1 energy level to escape from its hydrogen atom altogether.   That is a higher energy (and so a higher frequency, and a shorter wavelength) than the Lyman alpha line, and in fact corresponds to about 91 nm in the rest frame of the hydrogen atom.   Any photons that have even higher energies (and thus even shorter wavelengths) than this get absorbed by the (lots of) neutral hydrogen that is around in the Universe at that time; these photons thus *ionise* that neutral hydrogen.  This is sometimes referred to as “re-ionisation” in the sense that the universe was fully ionised when it was much younger, because it was much hotter, then it cools enough for neutral hydrogen to form – i.e. when the CMBR was emitted – and now it’s being ionised again.  Where are the high-energy photons coming from to do this ionising (being absorbed in the process)?  They are believed to come from hot young stars – i.e. the newly formed stars in these young galaxies.  (Remember, the more massive the star the hotter their surface temperature, so massive blue stars emit lots more of these energetic photons than cooler red stars do).

So, in summary, the spectrum of light from a galaxy as a whole drops off at the Lyman break, like a “cliff edge” because at shorter wavelengths than the Lyman break these photons get absorbed, ionising the hydrogen gas in their environments.

You can then play the same game as with an emission line: look for where this “cliff edge” appears in the observed spectrum and then use that observed wavelength (which will be much longer than 91nm) to estimate the redshift.

The research paper on GN-z11 is at https://arxiv.org/pdf/1603.00461.pdf, and is actually pretty readable I think…

Other references:

https://www.space.com/32150-farthest-galaxy-smashes-cosmic-distance-record.html

Another clear explanation from Prof. Hendry, who never makes us teachers feel silly for asking questions. Thanks to Mr Thomson and his student for the original question.

# Resources for Special Relativity

Here is a link to a fantastic little book that started me on my “very short introduction” library. It has been uploaded as a pdf file, but if you enjoy it give the author some credit and pay the guy (Russell Stannard) by buying it!

Relativity-A-Very-Short-Introduction.pdf

### Frames of Reference

You should all try to make your holiday videos so useful in showing Physics ideas! Who is in motion? Does it remain the same throughout the sequence?

This is covered in the web-based research post but I’ve uploaded it here as an MP4 file.

Just check this off against the content as it isn’t all covered at Higher (some is the AH and some isn’t covered at all).

Neil deGrasse Tyson with his inimitable style explains the Michelson-Morley experiment and shows that despite getting a rubbish result it doesn’t say your results are rubbish! This was big Science progress and it wasn’t explained until Einstein came along. It was the turning point that transformed Science.

Here are further explanations of the Michelson-Morley experiment and a hint of more of the course to come.

### Sixty symbols- Nottingham University

Sixty Symbols by Nottingham University are an amazing set of videos, although far more than sixty by now. Check out and keep watching.

…. and here at the end I have uploaded the worked answers (thanks to whoever wrote these excellent questions) so that you can check off your tutorials.