Category: AQA Unit 2 Forces/ Motion/ Waves

4 Waves

This topic a meaty one with plenty of learnt facts and calculations to build on the facts. You must write notes to help you remember the key points. Also try out the virtual links and further reading. However, don’t get too carried away with all the music stuff which can go pretty deep.

Resources

04 Waves Student Booklet

4.1 Waves and vibrations

04.1 Waves and Vibration

SHM Examples from IOP

4.2 Measuring waves

04.2 Measuring Waves

12_2_Dual_Beam_Results (Excel)

4.3 Wave Properties 1

04.3 Wave Props1

Riple Tank Simulation (Private Study – must do)

4.4 Wave Properties 2

04.4 Wave Props2

12_4_HSW_interference_using_microwaves (Practical or Data Exercise)

12_4_Superposition (Excel – Interactive addition of waves)

4.5 Stationary and Progressive Waves

04.5 Stat and Progressive

4.6 More about stationary waves on strings

04.6 Strings waves

Instrument_Frequencies (Html Table of Instruments)

12_6_String_Nodes_Results (Excel)

12_6_musical_scale (Excel – frequencies from Wiki)

4.7 Using an Oscilloscope

04.7 Using an Oscilloscope

Polarisation of Waves - A Level Physics

In the video I explain the polarisation of waves (including the polarisation of light) for A Level Physics.

Only transverse waves can be polarised, this video explains why. It also shows ...
why sunglasses are known as 'polaroids' and how you can test this yourself on a sunny day.

Update - Please note that the reflected light waves from water are actually horizontally polarised:
https://sureshemre.wordpress.com/2014/01/02/light-reflecting-off-water-is-polarized/
https://www.osapublishing.org/DirectPDFAccess/70EF21F6-C0C6-DC00-994222A32CB6DCEF_276371/oe-21-26-32549.pdf?da=1&id=276371&seq=0&mobile=no

Thanks for watching,

Lewis

This video is recommended for anyone studying A Level Physics in the following exam boards:
AQA
CIE
Edexcel
Edexcel IAL
Eduqas
IB
OCR A
OCR B
WJEC

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5 Optics

This section has some quite tricky concepts and really you need to look at the animations and play with the settings to get a feel for what happens to x when I change y etc..  You also need to learn the key diagrams as this will help your explanations. Finally look carefully at the derivations as they also will help you explain the tricky stuff.

Resources

05 Optics Student Booklet

5.1 Refraction of light

05.1 Refraction

13_1_Refraction_Practical (refractive index of a glass or a perspex block)

13_1_snells_law (practical results)

Refraction of Light (Java Applet)

Refraction Animation Shows Snell’s Law (Really Good)

13_2_Refractive_Index_Water_Prac (Refractive Index of Water)

5.3 Total internal reflection

13_3_Fiber_Optics_HTML (HTML summary)

05.3 TIR

5.4 Double slit interference

05.4 Double Slit Interference

13_4_Youngs_Slits_Practical (Hard to make this practical work but interesting method)

Diffraction of Light by a Single Slit (Java Applet)

Interference of Light at a Double Slit (Java Applet)

5.5 More about interference/ 5.6 Diffraction/ 5.7 The diffraction grating

05.6 and 5.7 Diffraction

136_Practical_Properties_of_micro (Practical investigation of properties of transverse waves

13_7_Diff_grate_prac (Investigation into diffraction 1,2,3rd order for laser beam)

13_7_Laser_Diffraction_Results (example results for red neon laser)

13.7 Spectrometer setup (Instructions)

resolving power of eye (extension for interest)

Image Formation by Converging Lenses (Java Applet)

Refracting Astronomical Telescope (Java Applet)

Amazing Refraction Magic Trick - The Appearing Beaker

Works on refraction and refractive index being matched.
 Title What to do Site Converging Mirror Lab Image in concave mirror PhysAviary Image formation in curved mirrors Images in mirrors Geobra Image formation in curved mirrors Images in mirrors Geobra Image formation in plane mirrors Images in mirrors Geobra Images in mirrors Mirrors Sim bucket Mirrors Images Boston Uni Mirrors and time Least time Boston Uni Name That Image Figure out image location/type of mirror Physics Classroom Optics Bench – Mirrors Use the bench to investigate images Physics Classroom Plane Mirror – How Tall? Images Boston Uni Reflection and the Role of Time Least time Boston Uni Who Can See Who Game to use mirrors Physics Classroom Reflection, Time, and the Law of Reflection Least time Boston Uni Refracting astronomical telescope Telescopes Fendt Total Internal Reflection TIR Boston Uni The Way a Mirror Works Lab (Concave) Curved mirrors – concave PhysAviary The Way a Mirror Works Lab (Concave) Curved mirrors – convex PhysAviary The Way a Mirror Works Lab (Plane) Reflection analogy PhysAviary Reflection and refraction Reflection/refraction Geobra Reflection and refraction of light Reflection and refraction Fendt Least Time Principle Drowned swimmer analogy Physics Classroom Refraction Investigate effect of angle, media Physics Classroom Rainbow formation Refraction Geobra Rainbow formation 3D Refraction Geobra Refraction Snell’s Law Boston Uni Refraction and the Role of Time Least time Boston Uni Refraction in a Block Snell’s Law Boston Uni Refraction Lab Refraction PhysAviary Refraction, the Role of Time, and Snell’s law Least time Boston Uni
 Title What to do Site Diffraction of Light by a Single Slit Diffraction Fendt Diffraction Lab Diffraction of Light PhysAviary EM Spectrum Lab Diffraction gratings PhysAviary RGB Color Addition Add different colours, explore uploaded image Physics Classroom Painting with CMY Change uniform colors and see effect Physics Classroom Color pigment mixing Color Geobra Color vision Color vision PhET Dispersion of light Dispersion Geobra Light mixing Color Geobra Coloured Shadows Make coloured shadows Physics Classroom Color Filters See effect of filters Physics Classroom Hit the Lights See effect of stage lighting Physics Classroom Double slit diffraction/interference Interference Geobra Double slit interference Interference Geobra Interference of light double slit Interference Fendt Thin film interference Interference Geobra Young’s Experiment Make measurements for double slit interference Physics Classroom Double slit interference with photons Interference Open Source Physics

Cross Winds Calculations..

Try out this game which is all about defeating a cross wind…

Bowman Game

This one is all about the angles and the Kinematics, looks simple but think about projectile motion…

https://www.animatedscience.co.uk/fun/bowman.swf

8 Equations of Motion…

A common problem for teaching Physics when you are not a Physics teacher is that you make many mistakes with complex ideas which appear simple on the surface.

I drop a ball to the earth and want to work out the distance fallen in a certain time. I then do a calculation of..

distance x speed = time

Oh dear but when I do the experiment it does not work like that but it works like this…

[latex size=”3″]s =\frac{1}{2}at^{2}[/latex]

Now we can reason this out. If I allow a ball to fall to earth it must accelerate due to the field of gravity around the earth 9.81N/kg. Or 9.81 m/s/s.

But where does the formulae  come from that we general use?

[latex size=”3″]s = ut+\frac{1}{2}at^{2}[/latex]

1. s = the distance between initial and final positions (displacement) (sometimes denoted as x)
2. u = the initial velocity (speed in a given direction)
3. v = the final velocity
4. a = the constant acceleration
5. t = the time taken to move from the initial state to the final state

So the question is what is it all about.

Well we need to think way back to the idea of a simple idea of how to work out the distance travelled by  a runner in a race.

Think of an athlete travelling 100m in 10s at a constant speed. His velocity or speed is…

[latex size=”3″] \frac{d}{t}= speed[/latex]  OR  [latex size=”3″] \frac{s}{t}= v[/latex]

Now this works fine if we are travelling at a constant speed but hey as you know this is not always the case and sometimes an object has a constant acceleration or deceleration. If you think about a graph of a person who got faster and faster then we would have a slope or triangular area on a speed-time or velocity-time graph. Now the area under the graph would be the distance travelled on the journey. But if our speed changed s=vt (for constant speed) becomes….

[latex size=”3″] s=\frac{vt}{2}[/latex]

Now you have an expression for the average speed but only from a standing start. Imagine now the same velocity time graph but this time the runner was already travelling at a velocity at the start of timing. Our area would become a triangle and rectangle…

[latex size=”3″] s=\frac{(v-u)t}{2}+ut[/latex]

Simplifies to

[latex size=”3″] s=\frac{(v+u)t}{2}[/latex]  – Eq 2

This is the formulae for average speed that takes care of all situations even when u or v is 0. Now then think graphically again if we are travelling at an initial velocity and then accelerate we are back to triangle and square again when looking at a vt graph. Hence…

[latex size=”3″] v=u+at[/latex]  – Eq 1

Now we can use this in a rearranged form..

[latex size=”3″] t=\frac{(v-u)}{a}[/latex]

Substitute into Eq 1 in new form into 1 to remove t so we now have an expression…

[latex size=”3″] s=\frac{(v+u)}{2}*\frac{(v-u)}{a} [/latex]

Which simplifies to..

[latex size=”3″] s=\frac{(v^{2}-u^{2})}{2a} [/latex]  – Equ 4

Now we have this we can work also work backwards to get Eq 3 …

[latex size=”3″] v=u+at[/latex]  – Eq 1

And *t gives..

[latex size=”3″]vt = ut+at^{2}[/latex]

Divide both sides by two…

[latex size=”3″]\frac{vt}{2} = \frac{ut}{2} +\frac{ at^{2}}{2} [/latex]

Add ut to both sides, multiply by 2 and tidy up..

[latex size=”3″]s = ut+\frac{ at^{2}}{2} [/latex] – Eq 3

So we now have the four equations of motion for an object which is travelling at a constant velocity or accelerating at a constant rate. As shown you can reason them all out with very simple ideas from first principals. You can also call them whatever number you want as some people label them differently.

So hopfully we have now understood where the formulae comes from and realise that if we drop a ball we must apply the formulae to work out the distance fallen in a more complex way.

Then it gets really interesting when you think about a tanker travelling at a constant velocity which then slows down. How far does it travel as it slows…

[latex size=”3″]s = ut-\frac{ at^{2}}{2} [/latex]

Of course, it will be ut for the whole time and then you take away a little bit of “s” from the other term as you slow.

New solar fuel machine “mimics plant life”

In the prototype, sunlight heats a ceria cylinder which breaks down water or carbon dioxide

A prototype solar device has been unveiled which mimics plant life, turning the Sun’s energy into fuel.

The machine uses the Sun’s rays and a metal oxide called ceria to break down carbon dioxide or water into fuels which can be stored and transported.

Conventional photovoltaic panels must use the electricity they generate in situ, and cannot deliver power at night.

The prototype, which was devised by researchers in the US and Switzerland, uses a quartz window and cavity to concentrate sunlight into a cylinder lined with cerium oxide, also known as ceria.

Ceria has a natural propensity to exhale oxygen as it heats up and inhale it as it cools down.

If as in the prototype, carbon dioxide and/or water are pumped into the vessel, the ceria will rapidly strip the oxygen from them as it cools, creating hydrogen and/or carbon monoxide.

Hydrogen produced could be used to fuel hydrogen fuel cells in cars, for example, while a combination of hydrogen and carbon monoxide can be used to create “syngas” for fuel.

It is this harnessing of ceria’s properties in the solar reactor which represents the major breakthrough, say the inventors of the device. They also say the metal is readily available, being the most abundant of the “rare-earth” metals.

Methane can be produced using the same machine, they say. Refinements needed  The prototype is grossly inefficient, the fuel created harnessing only between 0.7% and 0.8% of the solar energy taken into the vessel. Most of the energy is lost through heat loss through the reactor’s wall or through the re-radiation of sunlight back through the device’s aperture. But the researchers are confident that efficiency rates of up to 19% can be achieved through better insulation and smaller apertures. Such efficiency rates, they say, could make for a viable commercial device. “The chemistry of the material is really well suited to this process,” says Professor Sossina Haile of the California Institute of Technology (Caltech). “This is the first demonstration of doing the full shebang, running it under (light) photons in a reactor.”

She says the reactor could be used to create transportation fuels or be adopted in large-scale energy plants, where solar-sourced power could be available throughout the day and night. However, she admits the fate of this and other devices in development is tied to whether states adopt a low-carbon policy. “It’s very much tied to policy. If we had a carbon policy, something like this would move forward a lot more quickly,” she told the BBC. It has been suggested that the device mimics plants, which also use carbon dioxide, water and sunlight to create energy as part of the process of photosynthesis. But Professor Haile thinks the analogy is over-simplistic.

“Yes, the reactor takes in sunlight, we take in carbon dioxide and water and we produce a chemical compound, so in the most generic sense there are these similarities, but I think that’s pretty much where the analogy ends.”

The PS10 solar tower plant near Seville, Spain. Mirrors concentrate the sun’s power on to a central tower, driving a steam turbine

Daniel Davies, chief technology officer at the British photovoltaic company Solar Century, said the research was “very exciting”.

“I guess the question is where you locate it – would you put your solar collector on a roof or would it be better off as a big industrial concern in the Sahara and then shipping the liquid fuel?” he said.

Solar technology is moving forward apace but the overriding challenges remain ones of efficiency, economy and storage.

New-generation “solar tower” plants have been built in Spain and the United States which use an array of mirrors to concentrate sunlight onto tower-mounted receivers which drive steam turbines.

A new Spanish project will use molten salts to store heat from the Sun for up to 15 hours, so that the plant could potentially operate through the night.