Welcome to S6 Physics. This page will contain invaluable information which will help you through the year. Make sure that you bookmark it!

S6 23/12/05

Papers have moved to: http://www.geocities.com/rmackrells6

PHY4, PHY5 and PHY6 should all be available to you....

S6 14/12/05

Microwaving a little line of jelly babies with the turntable disabled led to some of them melting before others. The microwave works by setting up a standing wave inside it. Antinodes on this wave cause heating, nodes do not. By measuring the distance between antinodes we were able to determine the wavelength of the microwaves. The frequency of the microwaves was known and so we could make an estimate of the speed of the waves. We were coreect to within 2% (to known speed of light).

email rmackrell509@yahoo.com with any problems over the holidays.

S6 13/12/05

My word, long time no see. All available papers were distributed, including '05. RJE will be handing out some nice mark schemes for you tomorrow. I'll still put some in my pigeon hole for those absent.

S6 30/11/05

Single lesson - we started off on the PHY4 spec paper. We have Jan papers - RJE has summer ones to revise with.

HW Those Emmanuel school oscillations questions by next Tues.

S6 29/11/05

PHY3 and PHY1 papers were handed out to retakers - in by next week please. We did the corresponding practical that wasn't covered last week from the Practical exam past paper. We then continued to work through the oscillations questions booklet started last time.

HW Finish all oscillations questions by next Tuesday.

Heads up those doing resits! Loads of practise questions here - make use over the holidays of the mechanics or electricity ones.

S6 23/11/05

Exam question practise was continued with a rather good set of problems stolen from Emmanuel school's website. There were several absentees due to interviews and sundry other matters. We'll do some more practical practise next week and continue exam questions.

HW Do 5,6,7 from the nice handout.

RM's HW - Mitesh wants a PHY3 past paper, others need a new PHY1.

S6 22/11/05

We went through the large test. A honing of exam technique by writing clearer answers is required by many of you.

We then did a practise practical exam section, we'll finish this off next week by doing the one that you didn't complete this time. Remember to bring your papers please.

Then we watched the astronaut who came and gave a talk in the hall.

Ever wonder what science is? No answers here.

Check this A2 quiz site out though It's really good.

S6 15/11/05

We sat the large test. Then we watched "A Brief History of Time" about Stephen Hawking.

S6 09/11/05

The module is essentially finished for us. We looked at some of the questions from the cosmology chapter and then at a past exam paper cosmology question.

Here is another link, this time NASA's cosmology site. There really is no end of detail on the web on this topic...... More here and that's just the first couple of Google hits.

HW Revise for an all encompassing test on what we have covered on this topic. Circular motion, SHM, resonance, simple waves, polarisation and cosmology basically.

S6 08/11/05

No-one here so we watched telly instead.

Some of the videos discussed Einstein's general relativity which deals with gravity through mass bending a 4 dimensional space time.

This link may help to satiate your curiosity on this front.

S6 02/11/05

We talked some more about models of the universe. Hubble confirmed the expansion of the universe, but its continuing fate is not yet known.

Which model is fullfilled depends upon the density of matter in the universe. It is relatively easy to see how much luminous matter there is in the universe and work out its density. However, there is an unknown amount of "dark matter" in the universe.

Evidence for this comes from galaxy rotation curves

There are various possible types of dark matter, from planets around stars and gas clouds to MassiveAstronomicalCompactHaloObjects (brown dwarves around the edge of galaxies) and WeaklyInteractingMassiveParticles (exotic neutrinolike particles but with more mass)

More details can be found here The detail that you are required to know is much less as outlined by the single chapter in the book.

S6 01/11/05

We went through the AQA questions which were sat last time. Rather too many mistakes on the energy in shm questions here I thought.

A huge set of nice oscillation questions was got from the OCR syllabus this time. We had a go a several of these, leaving a fair few more to do.

The last bit of cosmology was then embarked upon. Hubble used the absorption spectra to measure the Doppler shift of light from various objects in the sky. He was able to identify that more distant objects are travelling faster away from us.

The methods of distance measurement such as parallax and standard candles were covered in astrophysics last year here

This gave rise to the idea of all matter in the universe starting out very much closer together than it is now (if the current expansion is simply time reversed).

More complicatedly, the idea is that not only all matter has got further apart , but that this is because space itself is expanding.

We tried the 2D "balloon universe analogy"

As the skin of the balloon stretches, the dots on the balloon become further apart, faster the further they are away.

Movie link here

The universe is thought to be something along the lines of a 4 dimensional hypersphere, such that all points in the universe will observe Hubble's law to be true (the curvature which we cannot detect is in a 4th dimension unknown to us).

Mindbending stuff, we'll talk about the dark matter problem tomorrow and that will wrap up our bit of the syllabus. Loads of extra reading you can do on this topic, I'll collect together some links at a later time.

HW In 1 week's time I need the "Harmonic Oscillators" bit of th OCR sheet done.

S6 19/10/05

We sat the test full of A level questions from the AQA syllabus.

PHY1 papers were handed out to resitters also.

S6 18/10/05

I was very knackered. Still, we ploughed on into new territory with some cosmology. Firstly, we looked at some emission spectra from some lamps. Electrons can only exist at certain "distances" from their nuclei due to their wavelike behaviour (The probability wave would interfere with itself otherwise.....) If you give the electron some energy by heating, it may well jump up to a higher "energy level" and get a bit further aweay from the nucleus. If it does this, it will fall down again, emitting a photon of a specific frequency.

Different chemicals have different characteristic patterns of spectra, we viewed several excited gases using a spectrometer. This makes use of the fact that longer wavelengths are bent more by diffraction than shorter wavelengths to split the light into its constituent colours.

In cosmology, absorption spectra are used rather than emission spectra, a pattern of dark lines against a rainbow background.

The above picture shows a complete spectrum, an emission spectrum and an absorption spectrum in that order.

This is what I wrote about it last year.....

We looked at spectral lines produced by different hot gases. Emission spectra are caused because of the limited number of distances that electrons can orbit their nuclei in each element. When excited by some external force the electrons "jump up" energy levels and often fall back down again. When they do this, they release energy in the form of electromagnetic radiation. The specific frequency of this radiation is proportional to the energy change that the electron has undergone. Each element has its own specific pattern of energy changes which are possible due to its unique electron structure. Therefore, when excited, each element produces a different pattern of frequencies of e-m radiation. In the visible range, we pick these up as different bands of colours. The light emitted by the excited gas must be seperated into its constituent colours by a spectrometer. When a full spectrum is shone through a sample of an element, the element absorbs the same frequencies that it would emit if excited, leaving dark bands in the spectrum. These missing frequencies form the same pattern as they would for an emission spectrum and are known as an absorption spectrum. These can be used by astronomers in a number of ways to discover things about the universe.

hmm...

The Doppler shift of the absorption spectra are used by astronomers to work out the speed at which light sources are approaching or receding from us.

HW A test on circular motion, SHM and waves will occur tomorrow.

S6 12/10/05

The last little section on travelling waves is simply a recap of GCSE calulations.

Wavespeed = Frequency * Wavelength

Distance travelled by a wave = Speed * Time (for echolocation)

We did some practise calculations, finish off Chapter 12 Qs.

We may do a proper little test before jumping into cosmology.

S6 11/10/05

We rather abandoned the last set of oscillations questions done due to the ambiguous nature of many of the questions and the odd mark scheme. Instead, mark schemes were handed out and we discussed the sense of the questions at least.

We completed some proper past exam questions instead which were far more straightforward. Remember to keep your calculators in radians mode for these calculations or the answers will be wrong.

Almost all the formulae you need are listed on the back of the exam paper, you just need to understand how to use them.

We started looking at travelling waves (as opposed to oscillations). An individual particle which is part of a travelling wave undergoes SHM. So a restoring force is neccessary, pulling a particle back to its equilibrium position in order for a wave to propagate.

You were reminded of the 2 types of waves:

transverse above, where oscillations of the medium are perpendicular to the wave motion.

and longitudinal, where oscillations are parallel to the direction of motion.

Waves carry energy, although there is no overall displacement of matter. (This is expressed as a sum of KE and PE in the wave just as in oscillations).

If the source of waves is sending them out in all directions, they will spread out in a spherical shape. This is the main reason for the fact that objects appear dimmer when further away (as in astro) and sounds are less loud at a distance.

The intensity of a wave is measured in Watts per metre squared.

Intensity = Energy recieved per second / area

The total power of a wave source is spread over an ever increasing area as you get further away from it. 4*PI*r² = the area.

So intensity as you move away from a spherical wave source diminishes by a factor of 1/2²

We also went into the polarisation of waves. This can only apply to transverse waves.

If all vibrations are in the same plane for a transverse wave, it is said to be polarised. Most 2D pictures you will see of transverse waves will imply that they are polarised. For light, particularly, this is rarely the case.

The picture shows a simplified picture of unpolarised light passing through a poloaroid which only allows vibrations at a certain angle through. The remaining light is now polarised.

2 polaroids at 90 degrees to each other will therefore not allow any light through.

But 2 polaroids at the same angle will allow some light through.

This is the principle by which simple LED displays work on.

Cross polaroids can be used for isomer identification in chemistry and for photoelastic stress analysis

You get the interesting colour patterns at points where stress exists.

HW Practise question 10.4

PHY1 resitters will get a new paper tomorrow

S6 05/10/05

Another holiday for the more Jewish types. We sat 3 questions on oscillations in a testesque enviroment so I could mark them nicely and have something to tell your parents about.

Simon wanted a sheet summarising oscillations. Well maybe if I have time later, but for now here is a link to some university slide show which goes through some circular motion and SHM.

HW Do the set of questions on circular motion - there's lots so I'll give you a whole week to do these. Max, Faris, William and possibly others owe me a PHY1. A new one will come to you next week.

S6 04/10/05

Jewish holiday. We went through some tricky examples of past A level questions on both oscillations and circular motion. We'll continue this tomorrow to avoid covering new stuff with considerable absences. I may be able to get some of the questions scanned in and available to downlaod, but it looks like it will be more convenient for those of you who missed the lesson just to come and pick up a hard copy from me on Thursday.

2 points were emphasised.

1 - you can calculate the maximum velocity of an SHM system using the formula:

Max velocity = Angular speed * Max displacement

2 - the formula for energy stored in a spring is:

Energy = 1/2kx²

This is useful for mass-spring SHM systems.

HW None - but sort out anything that you have got missing.

Damn it! I need those PHY1 papers in from all who haven't done it. Max etc. They aren't optional. I also need to get a new paper out to Jonathtan, Debodun etc.

S6 28/09/05

We went through the homework(s). Most of you seem to be OK with vertical circular motion now. SHM seems to be reasonably OK in its simple form, but make sure that you are reasonably accurate with sketch graphs. Also, I told you a barefaced lie about the relationship between force and displacement in an SHM system.

Of course, Force is proportional to minus displacement and so a straight line with negative gradient passing through the origin would be plotted for a force/displacement graph.

HW Complete the practise question on resonnance.?

S6 27/09/05

We looked at the energy changes involved in a system undergoing SHM. All SHM involves an interchange between KE and PE. For an undamped system, the total energy of the system remains constant, so KE + PE = constant. However, the system oscillates from having all KE, to all PE and back again. Different oscillators have different ways of storing PE (e.g. pendulum - GPE, horizontal spring - Elastic PE, etc.)

We then looked at forced oscillations. If an object is prompted to oscillate by an external vibration, it will respond very differently depending on the frequency of that vibration.

If the forcing frequency is close to the natural oscillating frequency of the object, it will oscillate with a very large amplitude. If the forcing frequency is significantly different then the forced oscillation will only be small.

The above shows resonance for light, medium and heavy damping. Notice the x axis is labelled in angular frequency instead of standard frequency. This makes no difference really, as we know that angular frequency is just regular frequency multiplied by 2 pi.

You are able to calulate the oscillating frequency of simple SHM systems like a pendulum or a mass on a spring. However, most ordinary solid objects will have a natural oscillating frequency of sorts.

It is very important indeed to avoid buildings, bridges etc. being forced to oscillate at near their natural frequency, or they can respond by oscillating so much that they are destroyed.

HW Do questions 8.2-8.5 on energy changes in SHM.

S6 21/09/05

You are given 2 formulae for the period of oscillating objects on the back of your exam paper. One is for the period of an oscillating mass-spring system which you tested experimentally yesterday.

The other is for the period of an pendulum swinging at small angles. We attempted to test this one today, with period T being proportional to the square root of the length of the pendulum, l.

Finish those graphs, we'll check the gradients next time.

HW Vertical circular motion question sheets for next time.

I'll include this link again, have a look. SHM quizzes and the like.

S6 20/09/05

Another treble marathon. We performed an experiment to test the oscillation of a mass hanging on a spring. We assumed that it was undergoing shm (reasonable as we know that a spring obeys Hooke's law). We measured the period T, for various masses. Analysis of the shm formulae allowed us to plot a straight line graph using the angular frequency and sqrt(1/m) which allowed us to make a measurement of k, the spring constant of the spring. We then directly measured the spring constant using a force vs extension graph.

Those who got there found results which were similar, certainly not bad for results obtained from 2 error prone experiments.

Check out this little shm self test thing. Pretty ace.

HW

• Get your graphs finished and calulate your measurement of k if not done already.
• Do practise Qs 5.3 and 5.5 for tomorrow please. Other circular motion practise questions were handed out but don't need to come in until next week.

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Einstein said, "God does not play dice." If I was omniscient I definately would....

S6 14/09/05

Shortist lesson compared to yesterday. We discussed the homework, silly mistakes mainly. We then continued to look at simple harmonic motion.

Ironic that the only picture I can find to steal is shocking and hand drawn anyway.....

The velocity of an oscillating object can be found from the gradient of its displacement against time graph and the acceleration from the gradient of the velocity against time.

Acceleration is proportional to negative displacement at all times for this type of motion.

We have shown how this appears graphically, and I went through the mathematics although differentiation will not be required for Physics A level.

The HW sheet was taken in. I may have misplaced William's HW but Faris needs to hand his in.

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Economics is the only field in which two people can get a Nobel Prize for saying exactly the opposite thing.

S6 13/09/05

The first triple lesson marathon took place.

HW was taken in (chapter 2 practise Qs)

We looked at circular motion some more. Firstly, circular motion in a vertical circle. All the same rules apply, but the weight of the object moving in the circle must be taken into account.

The centripetal force = mv²/r

but when at the top of its circle, the weight of the object acts downwards, forming part (or all) of the centripetal force required.

At the bottom of the circle, the object's own weight must be supported in addition to the centripetal force required.

e.g. if an object is whirled around on a piece of string in a vertical circle, the string will have the most tension at the bottom of the circle, and is most likely to break there.

We also looked at conical pendulums. An object moving in a horizontal circle supported by string from above. Here the tension in the string must be resolved into vertical and horizontal components.

The vertical component of the tension supports the weight of the object. The horizontal component provides the centripetal force to keep the object moving in a circle.

Finally, we began to look a little at oscillations. We particularly look at simple harmonic motion in Physics where a force always acts to pull an object back to a central (equilibrium) position. The further the object is pulled from equilibrium, the larger the force pulling it back. This type of oscillation has a constant period.

HW Past paper question on sheet.

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What's the difference between mechanical engineers and civil engineers? Mechanical engineers build weapons. Civil engineers build targets.

S6 09/09/05

This lesson shall be moved for the mutual convenience of all. We will now have a triple(!) Physics lesson on Tuesdays, going through into the lunch hour.

Today we looked at quantifying the acceleration and forces involved in circular motion.

A proof was shown that the acceration is v²/r

So the centripetal force is: mv²/r

We also looked at a notation for circular motion involving angular speed (measured in radians). This is represented by the Greek letter omega.

All the circular motion formulae can be re-written in terms of omega.

HW All chapter 2 practise questions P55

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There are 10 kinds of people in the world..... Those who understand Binary, and those who don't.

S6 07/05/09

It was delightful to see you all again. Books were issued and numbers taken. We started the new module very briefly with a look at circular motion.

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Heisenberg is out for a drive when he's stopped by a traffic cop. The cop says 'Do you know how fast you were going?' Heisenberg says 'No, but I know where I am.'