Welcome to 5th form Physics. This page will contain invaluable information which will help you through the year. Make sure that you bookmark it!

12/12/05

We revised electronics. All that you needed to know was listed on the board - resistor colour codes, logic gate symbols and truth tables, potential divider calculations, transistors as switches turned on by a high enough voltage at the input, thermistors and LDRs as input sensors, capacitors as time delays (they take some time to charge up to full voltage, the time taken can be increased by putting them in series with a larger resistor or increasing the size of the capacitor), relays must be used to make a transistor circuit operate a high power device, a reverse biased diode is needed to stop the relay breaking the trasistor. Then on to electromagnetism.....

Electromagnetism revision links

BBC

S-cool

Uses of electromagnetism

Generators

Brilliant set of exam style electromagnetism questions - with answers!

You'll be given papers for revision next time.

08/12/05

You got the mark scheme for the OCR past paper. We looked at the 1998 paper.

Electromag. and control in circuits next time.

05/12/05

We did a quiz based on all of the formulas that you need to know for GCSE. I also gave you a formula sheet which told you all of the formulas, which was convenient.

HW OCR finished for Thursday, we'll look at the mark scheme.

01/12/05

Revision was begun in earnest with a look at an OCR GCSE paper. This needs to be finshed off for next Thursday's lesson. We'll do something on all the formulas that you need to know on Monday. Here are most of them.

HW Moments GCSE questions form those who haven't yet handed them in - important. Complete the OCR paper for next Thurs.

28/11/05

We continued to look at moments and centres of mass. This time, we started doing a set of GCSE questions on the matter.

HW Finish off the GCSE questions to hand in next time along with P173 Qs 1,2,3 if not already done.

24/11/05

RM at table tennis. You all had a go at the GCSE specimen paper as a start to mock revision. Remember the work I want to take in for next time which is listed below.

21/11/05

I need to take in from all of you: p173 Qs 1,2,3

We recapped the idea that hydraulic machines can be used as force multipliers. The pressure in 2 connected parts of a fluid will always even out, so they can be used to transmit a force. If you create a large pressure by exerting a force on a piston with a small area, elsewhere the same fluid can be fed into a piston with a much larger area and the equal pressure will exert a much larger force. However, the large force is moved only a small distance just like in levers.

We then looked at turning forces. You did these in the second form - here is what I had to say about them.

We looked at turning forces. This is all based around the idea of balancing seesaws. All the turning forces trying to make an object turn clockwise must be balanced by the forces trying to make it rotate anti-clockwise if it is in equilibrium.

The name for a turning force is a moment

Moment = Distance from pivot times Force

If the system is balanced, the anticlockwise turning effect of force F must equal the clockwise turning effect:

clockwise moment = anticlockwise moment

Clockwise moment = 5 N � 0�50 m = 2�50 Nm.

Anticlockwise moment = F � 0�25 m = 2�50 Nm

Force F = 2�50 Nm � 0�25 m = 10 N

In order to balance the 5 N force acting at 0�5 m from the pivot, we require 10 N acting in the opposite direction but at 0�25 m.

Turning forces are also involved in the measurement of centre of gravity.

You have covered this before too....

The centre of mass is the point at which the weight of an object appears to be acting through. (e.g. it will balance if held from this point. If you slice an object in 2 through it's centre of mass, there will be an equal mass both sides.

The centre of gravity needn't actually be inside the object.

For an object to be stable, it must have centre of mass which is not easily moved beyond its base of support.

A low centre of gravity and a wide base are therefore required.

A very stable object above, with a cog below its support.

HW P173 Qs 1,2,3

17/11/05

RM absent at CCF. Cover work from PTA on a variety of topics was attempted.

Ever wonder what science is? No answers here.

15/11/05

We went through the test which was encouragingly well attempted.

We then looked at some simple pressure questions.

You were reminded that the pressure in a fluid on Earth increases with depth. In the Earth's atmosphere, sea level is the "deepest" point and the air pressure falls the higher you go.

10/11/05

We sat the test on waves and then recapped pressure.

Pressure = Force/Area

It is measured in Newtons per metre squared (N/m²) or Pascals (Pa)

We saw the old demos of the pressure which is exerted by the Earth's atmosphere using a vacuum pump.

A saggy balloon becomes inflated when the air is sucked out from around it by the vacuum pump.

We failed to crush the can using the vacuum pump, perhaps we'll try again next time.

HW P165 Qs 1,2,3

07/11/05

Hooke's law was recapped with a quick go at the experiment that you did in the 2nd form - stretching a spring using weights. This is back on the syllabus after a while, so not many past paper questions on it.

You will have got results somewhat like those above, with the extension (amount that is has got longer by) of the spring being directly proportional to the force.

The graph would not always remain a straight line however. When too large a force is exerted on the spring it will permanently lose its shape. It is then said to have gone beyond its elastic limit. Force and extension are no longer proportional, so the graph loses its straight line shape. Note: the axes on the above graph are different, but stress can be thought of as equivalent to force, and strain as equivalent to extension. The axes are therfore reversed compared to the first graph.

HW We will have a test full of GCSE questions on Seismic waves, ultrasound, em spectrum and basic waves. I will continue to do this until you all get at least a B!

03/11/05

More on plate tectonics, this time focussing on the waves produced when an Earthquake occurs.

You must know about the 2 types, and also that the transverse S waves can only travel through solids, but longitudunal P waves can travel through both solids and liquids.

The outer core of the Earth is molten, meaning only P waves can penetrate it. The path of both types of waves are curved through the Earth. The Earth gradually increases in density as you get deeper which increases the speed of the waves, causing them to refract.

The boundaries between layers in the Earth have abrupt changes in density which sudden refraction, or sometimes total internal reflction. This leads to certain "blind" spots around the world which won't pick up any Earthquake waves at all when one occurs.

HW You completed nearly all the sheets I managed to throw at you, but I want to take in the waves Qs 4-6 and both sides of the sheet 3.9-3.10 if you haven't handed them in already.

31/10/05

Sadly, we have to divert into Geography for a bit. We learned about the theory of tectonic plates postulated by Wegener. It was only widely accepted in the 1950s, surprisingly recently for something that is now fairly common knowledge. The plates are kept moving by convection currents in the Earth's core. The core is kept so warm by radioactive elements decaying, otherwise it would have cooled off billions of years ago.

There is a link to waves however, the Earthquakes caused by friction between the moving plates transmit their energy through the Earth's crust via different types of waves. Longitudunal "P" waves and slower transverse "S" waves.

Great stuff here on plate tectonics.

HW Sheet on plate tectonics.

20/10/05

The single most apalling effort I have ever had the misfortune to preside over in the test sadly.

We went through the answers and with luck you were able to glean where you were going wrong. More GCSE waves questions were therefore set over the half term for you to do.

We then recapped optical fibres.

Advantages of optical fibres over electrical wires are:

1. Many more signals can be sent down one individual fibre than an individual wire.

2. Each individual fibre is very thin so you can bundle hundreds together and still have a small, light cable.

3. Fewer repeater stations are needed when sending signals long distances (the signal doesn't die away very quickly).

4. Optical fibres cannot be tapped without interupting the signal, so are much more secure.

5. The raw material for making optical fibres is very abundant - sand, much more so than copper.

There are a couple of disadvantages: It is hard to join (splice) optical fibres together accurately. Also, the very careful manufacturing process required for optical fibres means they need high technology and expensive factories to make them.

We also discussed the differences between digital and analogue signalling.

Analogue signals are continuously variable, digital signals are can only take a set number of discrete values, usually just 1 or 0 (i.e. they are in binary). Digital signals do not lose information when subject to interference or attenuation (getting weaker), as the code remains the same.

HW The set of more GCSE questions.

17/10/05

We sat a little test full of waves GCSE questions.

13/10/05

We covered the electromagnetic spectrum. All electromagnetic waves travel at the speed of light (300000000m/s) and can travel through a vacuum. They are really waves that are travelling vibrations in electric and magnetic fields.

All objects which have a temperature above absolute zero will emit some form of electromagnetic radiation. The higher the temperature, the smaller the wavelength that is emitted.

You are required to know the names, rough wavelengths, uses and dangers for each of the main areas of the spectrum.

If you missed the lesson I suggest that you read this or this (dubious nmenomics) website, or look at the table below from BBC bitesize.

HW Revise for a test on waves, includes uses of ultrasound and simple wave calculations.

10/10/05

We saw a laser diffract and did a few a questions along with a summary of the simple facts that you have to know about waves.

Above, a thin laser beam is shone into a diffraction grating, the light spreads out from each individual tiny slit and the resulting waves interfere with each other creating the pattern.

Light is very rarely seen to diffract due to its very small wavelength (between 4 and 7 10 millionths of a metre). In order for noticeable diffraction to occur the wave must pass through a gap which is similar in size to its wavelength. (Note, waves also diffract around obstacles which are similar in size to their wavelength.)

HW The GCSE thermal energy transfer questions, wave sheet 3.1 and the wave booklet need to be handed in by all for next Monday (after all have had a chance to pick up a copy.)

06/10/05

We did some practice questions on waves, specifically on:

Wavespeed = Wavelength multiplied by frequency

and echo location.

We looked at a wave tank demonstrating the 3 main properties of waves, reflection, refraction and diffraction.

Here is the website with the cracking animations giving examples of all of these effects

Reflection: Waves reflect off plane surfaces at an angle which is equal to their angle of incidence.

Refraction: Waves change direction when they enter a medium which slows them down. The wavelength is reduced, not the frequency.

Diffraction: Waves spread out when passing through a gap. The smaller the gap, the more spread out the waves become. If the gap is much larger than the wavelength, then diffraction less unnoticeable.

HW Finish the booklet of waves questions. We will make notes on all 3 next time as I promised Yates.

03/10/05

We started to recap waves. This was a large topic in the 3rd form, but it is necessary for you to kmow a bit more this time around.

Waves transport energy from one place to another with no overall movement of matter. The energy is transported as vibrations (a combination of KE and PE) through some medium.

Waves come in 2 major types, transverse and longitudunal.

In transverse waves, vibrations occur which are perpendicular to the direction in which the wave is travelling. e.g. water waves, light.

Longitudunal waves have vibrations which are parallel to the direction of wave travel.

This site has excellent animations of the 2 types of waves.

In fact, I'll try and put them up here.....

transverse above

and longitudinal

Important quantities that you need to remind yourself of are:

1. Amplitude - the maximum "height" of the vibration. Easy to see in a transverse wave, not so easy in a longitudunal.

2. Wavelength - The distance from the peak of one wave, to the peak of the next. It can really be measured from any point on the wave, to the next equivalent point.

3. Frequency - the number of waves which happen per second (measured in Hz)

Related to the frequency is the Period (T) which is the time taken for one wave to happen.

The big formula for you to use in waves is as follows:

Wavespeed = Wavelength multiplied by frequency

HW Answer the waves sheet given to you. I didn't take in the GCSE thermal questions from all of you, don't forget them next time please.

Sandro - coursework

29/09/05

We practised almost every possible GCSE thermal energy transfer question. That leaves us free to get on with waves next time.

HW Finish off the past paper GCSE questions (questions on a saucepan and a motorcycle engine) if you haven't already done so.

POAE from all by Monday or a detention sets in.

26/09/05

Convection: Happens in liquids and gases (fluids) that are in a gravitational field. One part of the fluid is heated and the particles begin to move faster and in doing so, get further apart. This reduces the density of the warm part of the fluid. The warm part of the fluid therefore starts to "float" up above the cooler less dense fluid surrounding it. Cooler fluid then moves in from the side to replace the warm, less dense, rising fluid. This fluid then starts to be heated, and so rises itself. Once the warm fluid has risen, it may cool and start to drop back down past the warmer fluid being heated beneath it. This causes a circular convection current to be created.

We saw 2 demonstrations of convection: 1 - tea leaves in a beaker of water heated by a Bunsen, 2 - a mock up of a mine with 2 vertical shafts and a candle lit under one of them (this allowed fresh air to be drawn into mines).

The lab hot air balloon was observed, it rises due to the particles in hot air being further apart than those in cold air (as they are moving faster), making the air less dense. It floats up on the rising air which is part of a convection current.

"Radiators" actually heat rooms by causing convection currents, hence it doesn't matter what colour they are painted really (although black would be a more efficient emitter of heat radiation).

HW POAE in for Thursday.

21/09/05

Final coursework session. I went through what is needed in the Evaluation section, and then we went to the computer room to work on it.

POAE will be taken in next Thursday and returned (eventually) with a mark. We are now back to normal in lessons, continuing heat transfer.

19/09/05

We looked at 3 demonstrations of conduction of heat. Conduction is where heat energy is transferred through a material via collisions of particles. As hotter particles move faster, they tend to hit other particles and give them more energy, passing energy heat along the material.

Metals conduct heat the best as they have free electrons which can move through the material carrying heat energy as they go. Liquids and gases are poor conductors as particles collide far less often in this state.

Radiation of heat: Heat energy can travel through a vacuum in a straight line away from a warm object. This is know as heat radiation or infra red radiation. It is just like light, but invisible to the naked eye.

Black objects absorb heat radiation best (as they do light) and so warm up the most when infra red is shone on them. White or silver objects reflect most heat radiation and heat up less.

Black objects emit heat radiation best too, so if a hot object is black, it will emit more radiation than a white or silver object at the same temperature.

HW Analysis will be taken in on Thursday.

15/09/05

I went through the requirements for the Analysis section of your coursework. 2 graphs are required, one of which contains processed data (bounce efficiency for example). Laptops were about for you to get started. Sandro and others still owe me P and O.

P and O sections were taken in.

HW Complete the A section to be handed in for next week.

12/09/05

RM absent.

08/09/05

We went to 306 to get some more coursework done. The deadline for the P and O sections is next Thursday. We will spend a couple of weeks getting coursework out of the way and then begin the 5th form syllabus.

HW Coursework, clearly.

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Two atoms bump into each other. One says 'I think I lost an electron!' The other asks, 'Are you sure?', to which the first replies, 'I'm positive.'