Quantum Physics – with a Coin

Find a coin.

Go on, rummage in a pocket, purse or wallet and find something a reasonable size like a UK 2p or 10p coin, about 1 inch or 2.45cm in diameter. This is all you need to explain quantum physics to someone.

Yes I did just say quantum physics. Surely that’s only for geniuses you cry! Quantum physics is a subject that intrigues and is hopelessly misunderstood in equal measure. This little demonstration will really impress your friends and explain all the basics of quantum physics in simple language. Let me show you how.

I’m assuming you can toss a coin. Throw it up and catch it then slap it down on the back of one hand. Did you get heads or tails?

Quantum Physical States and Probability

The only outcomes possible in a coin toss are heads or tails. You can balance a coin on its rim if you are careful and have a flat table, but that outcome never occurs in a coin toss, due to the slapping-it-flat-on-the-back-of-your-hand action.  There is no way to get heads and tails at the same time as they are on opposite sides of the coin. So I’m going to go ahead and say that the result of a coin toss is one of two possible states, either heads or tails.

Toss the coin a few times and you’ll find out that the number of heads and number of tails usually balance out. You should have an unbiased coin. This would mean the chance of getting a head each time you toss is the same as the chance of a tail, 50:50 chance of either state.

What if we suspected one side had been weighted and so the coin was biased? Tossing the coin hundreds of times would give us a very reliable way of finding if it had been tampered with. The numbers of heads and tails should balance out. If 40% of the time the coin’s state was found to be heads and 60% tails we know it is biased towards tails.

Tossing the coin allows us to find out information about what states are possible and what is the chance of ending up with any one of those states.

Now we’ve established that, what state is the coin in before you catch it?

You might say “no state” but that would mean there was no head-ness or tail-ness there at all, nothing. That’s not quite right as the coin is there. You can see it spinning in the air. How do you describe that?

 

Superposition in Quantum Physics

Quantum physics has a neat word for describing the mixture of head-ness and tail-ness that a spinning coin has before you catch it. The word is superposition. Superimposing is a technique used in photography or film where one image is put on top of another. The final image is a composite of the two. Superposition is a bit like that.

The spinning coin is not devoid of states, we can’t say it has no heads or tails to it. Instead it is a constantly changing superposition of the two states. This superposition tells us nothing about what state this unique toss will end in. That depends on all sorts of things like how fast it is spinning, how high we throw it, when we catch it etc. It won’t help us work out the outcome of an individual throw.

The superposition does contain information about any bias in the coin. As it spins, a heavier side to the coin will spend more time at the bottom of the spin and the lighter side would spend more time at the top. There is some information there we could extract about how the pattern of heads and tails would look after 100s of throws, if only we had a way of measuring it.

 

Taking A Quantum Measurement

You already know how to measure the state of the coin. You catch it and slap it down on your hand. Look at the coin and there is your measurement.

But this involves permanently altering the condition of the coin. You are forcing it into one of two possible states. When I measure my height I don’t force a mixture of all possible heights into 5 foot 10 inches. There is no probability of getting anything other than 5’10”. This measurement of the coin is different to normal measurements. The act of measuring the system we are interested in (the spinning coin), fundamentally alters the system we are interested in. Bummer.

There is no way around this I’m afraid. To get information about the possible probabilities of either heads or tails we toss the coin 100s of times. Then we interfere with the spinning superposition each and every time, forcing it into a single state. Only by repeating this measurement over and over do we get enough data to work out a pattern.

This is true of quantum objects like electrons. It is called The Measurement Problem. Only in quantum physics does the act of measuring the system permanently change the system. Or to put it another way, extracting information from the superposition destroys it. This is called collapsing the wave function.

What is a Wave Function?

Waves bob you up and down in the sea or make use of your hand to signal your departure or arrival. In both cases something is oscillating between two positions over and over. Up and down on the sea and side to side with your hand.

Lots of natural phenomena can be described using the language of waves. The variation in light intensity due to day and night, seasonal mean temperature changes, hormone levels in menstruating women, anything which has a repeated variation across a range of values is wave-like.

Physicists use the mathematical language of waves to describe quantum states. The spinning coin has a repeated variation in a range of values, it flips from heads to tails and back again as it spins. We can use wavy maths to describe this variation. The mathematics of waves is even more helpful as it allows us to add waves on top of each other and work out the resulting wavy shape. Like different tides or ripples interfering with each other at a point on the sea.

The spinning coin has a changing superposition of the heads and tails states. The chance of measuring either state depends on which way up the coin is pointing when you catch it. As the coin rotates it is found in a 100% heads state only once each rotation and only for a very short time, likewise for the tails state. The the rotation moves one side of the coin slightly higher and the amount of “heads” reduces slightly and the amount of “tails” increases. Or more correctly the probability of getting heads reduces slightly and the probability of getting tails increases slightly. So the chance of ending up with heads or tails is continuously changing as the coin rotates. If you plotted the probability shape on a graph it would rise and fall and rise and fall just like a wave.

The wave function is the name given to a mathematical wave shape which describes this varying chance of getting a particular state in a measurement.

Collapsing the wave function forces a single state on the coin, in this case either of the extreme positions, giving a head or tail.

 

Now the Quantum Physics Bit!

All this talk of coins is preparing us for the big moment to tie all this in with teeny tiny quantum particles.

There is an experiment which shows exactly what we have been talking about with coins, but with electrons. It’s called the double slit experiment. It is the classic way of introducing people to the weirdness of the quantum world. Electrons behave like a wave superposition of states until you force a measurement on them and then they behave like a lump with a fixed state.

Instead of throwing electrons up and down and catching them with some clever laser trap equivalent of a coin toss (or something!), the electrons are thrown at a screen. The screen can detect the hits from the electrons and emit a tiny light burst. So a pattern builds up showing where the hits occur.

When you shine a wavy source, like a torch, on a screen you get a bright spot in the middle and it gradually dims as the light spreads out at the edges. If you fire a lot of blobs at a screen there is a big build up of bobs in the middle and fewer out to the sides. It is hard to tell one result from the other.

So the physicists put something in the way of the screen. A big sheet with two narrow slits in it.

quantum double slit experiment

Diagram of the double slit experiment from Wiki-Commons

Now you can tell the difference between the pattern produced by wavy things and the pattern produced by blobs. Waves overlap and produce a new wavy pattern as shown in the picture above. The blobby particles are simply split into two streams of blobs by the slits and produce two splats on the screen. No superimposing happens for them.

Electrons are supposed to be blobs not waves. They are particles. When a beam of electrons is fired at the slits they start to build up a pattern on the screen. The pattern is a wavy interference pattern!

quantum double slit interference pattern

Each dot represents the impact of an electron on the screen. Many hits build up to produce an overall wave interference pattern, even though electrons are particles. This is evidence of the wave-particle duality of electrons. Experiment performed by Dr Akira Tonomura in 1989 at Hitachi. Creative Commons ShareAlike licence.

Here we are looking at information contained in the wave function of the electrons. Only when hitting the screen are they being forced into a state. Then their position state is fixed to a definite value. Just like the coins spinning in the air contained information about the probability of heads or tails, so the electrons shooting towards the screen contain information about the probability of where they will show up in the interference pattern.

We can collapse the wave function earlier on and force the electrons into a position state much sooner if we measure them. We can put a sensor on the double slits and record which slit the electrons go through. This destroys the supposition of location states and forces the electron to be in the left or right slit. Like catching a coin destroys the supposition of heads or tails and forces the coin to be one or the other. Then the electrons behave like blobs and build up in two patches on the screen. The waviness of the electrons has been lost.

This experiment was astounding. To actually see the theoretical wave nature of the electrons supposition and then be able to collapse the wave function and bring their blob nature back again has boggled many a mind over the years. Tiny particles can be waves or can be blobs depending on how they are interacting with their surroundings. Some interactions collapse the wavy behaviour and force the electrons into a fixed state. What we understand as measurements always collapse the wavefunction because our measurements require a value, a fixed state to give a result.

Conclusion

Tossing a coin will never look the same again! Each time you catch a coin you can think about how every photon of light hitting your eyeball has just collapsed its wavefunction, every click of the TV remote, every interaction of microwaves with food in your kitchen is a quantum measurement happening in front of you.

Now we need to talk about Schrodinger’s Cat…

schrodinger's cat experiment

A thought experiment proposed by Erwin Schrodinger. Picture from https://www.nobelprize.org/educational/physics/quantised_world/

Work Done in Physics

work done example - cable car

Work done is a boring topic. It is the very definition of a boring topic, even the name of this physics concept is dull. The word “work” doesn’t exactly make you jump up with excitement in the same way as “explosion” or “play” might, does it?

The definition of work done also seems very arbitrary, force x distance. Why? Why should we care about something defined as force x distance? Then you are expected to rote learn that work done is measured in joules, the unit of energy, but it’s not an energy store because it’s work done. Got that? This is just confusing to the average student.

Often work done is taught along with a demonstration of something being lifted up like the ski lift in the picture. Maybe the class sets out to find the work done by a person climbing stairs by firstly weighing the person then finding the height of the staircase. You are informed that motion in a horizontal direction doesn’t get included, no work done walking across the room. This contradicts the common experience of getting out of breath when walking quickly. Surely I’m doing work? The term work done also crops up in electrical circuits too where there are no stairs. None of it ties together very well. Ask for help from a teacher and the reply is usually, “that is the definition of work”!

There is an way to think about work done which makes a whole lot more sense! Imagine for a moment that we are stepping into a chapter of the brilliant series Horrible Histories, I would like to take you back to the Industrial Revolution.

 

Pit Ponies and Barges.

Back in ye olden days when there were no motors or even steam engines, heavy things were moved by teams of people or horses. Horses were used in mines to haul carts full of ore and coal, and to pull things up from the mine to the surface. Barge horses were used to pull canal barges laden with goods along canal ways.

winching children into a mine shaft

Two children are lowered down the mine-shaft to the coal- face by a woman working a winch Date: 1842 Source: ‘The Condition & Treatment of the Children employed in the Mines & Collieries of the United Kingdom’, page 7

And yes just like in Horrible Histories, young children were hand cranked down dark mine shafts to chip away at coal and mineral ores in polluted air with nothing more than a candle for company. Makes double maths look slightly more appealing.

 

winding horse whim

A sepia photograph of a winding-horse whim from Wheal Geevor Tin Mine copyright of Geevor Tin Mine and Pendeen Community Heritage, permission given for education use.

 

canal barge horse

A working canal barge with horse pulling the barge along, approx 1900

Then came the invention of steam engines and machinery to automate this process. It was important for the new industrial engineers to be able to explain their machines in a language that the mine owners could understand. They used the term “horse power”. This is the machine equivalent of the work that could be done by an average horse. Horses being more useful than small children.

Do you notice how the term work done slipped into that sentence? What work was being done here? In each example a heavy object is being pulled some distance by a horse. Pulling is an example of a force. The depth of the mine shaft, the length of the tow path, these are distances.

Now the definition of the work being done by the horse makes a bit more sense. The horse has to do some physical work to move an object a distance along or up. The horse has to pull, so there is definitely a force involved. In the mine the pull is upwards to overcome the downwards pull of gravity. On the towpath the pull is forwards, but what is the horse pulling against? Not gravity this time. The horse pulls against the water as it drags the canal barge forwards.

So the work being done by the horse is the result of the force it has to use to move the object and the distance it has to be moved.

A machine like a steam engine would need to be as good as, or better than, the work that could be done by a horse. That would make the steam engine attractive to potential buyers.

 

Defining Work Done

The term work was first adopted in the 1820s. There is a reference by the French mathematician GaspardGustave Coriolis in “Calculation of the Effect of Machines, or Considerations on the Use of Engines and their Evaluation“. He used it in the sense of a “weight lifted through a height”, from  the use of early steam engines to lift buckets of water out of flooded ore mines.

A “weight lifted through a height”, was also the way Sadi Carnot defined work in his famous paper Reflections on the Motive Power of Fire in 1824. Carnot said:

We use here motive power (work) to express the useful effect that a motor is capable of producing. This effect can always be likened to the elevation of a weight to a certain height. It has, as we know, as a measure, the product of the weight multiplied by the height to which it is raised.

Now hopefully you can see how work done = force x distance was a really useful quantity to a Victorian engineer.

A horse hauls 500kg up a 20m mine shaft. What is the work done by the horse on the load? (take g = 10 m/s^2)

 

A barge horse is pulling a barge with an effective mass of 8000 lb along a river for 1km. 1kg = 2.2lbs. Covert the weight to kgs and calculate the work done by the horse on the barge.

 

A steam engine can do the work of 4 horses. One horse can move 600kg a distance of 3km in 1 hour. How much work can each horse do? How much work does the engine do in 1 hour? What is the power (joules per second) of the steam engine?

When something moves it has kinetic energy. By doing work the horse is getting some heavy object to move. No movement and no work has been done. If the thing doesn’t budge, even though the horse might be straining all its muscles, in the strict physics sense no work has been done.

Giving these heavy barges and piles of coal some kinetic energy is what the horse is for. The horse’s store of chemical energy in its muscles slowly runs down while the heavy barge’s kinetic energy store slowly fills up. There has been a transfer of energy from one to the other through the action of the force. Work done is an energy transfer process. It is not a store of energy but a way of showing energy in flux. It is an amount of energy going from something that exerts a force to make something else move. This is why it is measured in Joules. It is the amount of energy being reduced in the horse to make the kinetic energy of the barge increase.

Amount of energy reduced in horse = amount of energy gained by barge = work done by pulling.

The work-energy principle basically sums up what this red equation says. An increase in the kinetic energy of an object is caused by an equal amount of work done on the object by the force acting on the object.

Work done fits nicely into our ideas about the conservation of energy. It allows us to explain why energy isn’t lost or destroyed by the horse when we get something moving. The changes in energy are a measure of the work being done to move the thing.

 

Generalising the Concept of Work Done

Physicists are practical people. If they come up with a new idea then they are going to look for different ways to use it. This makes life easier as you then have fewer laws of physics to learn. In fact some physicists devote their lives to finding the fewest number of rules you can have to describe the interactions of all things.

Theory of everything cartoon

Calamities of Nature cartoon Strip from 2012

Work done gets taught to school students because it is one of those concepts which has lots of practical applications. It can be used in many different areas of physics. Any time a force is acting on something and it moves you can say work is being done.

Hopefully you can see how work done by a horse depends on a force (due to the horse pulling on a weight) and a distance. To make this more general we can remove the horse altogether. Imagine a force acting on something that moves that thing some distance. We don’t need to worry about the actual object doing the pull (or push). We only need to think about the force involved and the distance moved. When the force only pulls in one direction we only include movements that are in that direction in our calculation of work done.

How about a tractor beam from the Death Star pulling on the Millennium Falcon? Or a magnet pulling the cover of a bag shut. Or a strong wind propelling a windsurfer. Or the negative end of a battery pushing away negative electrons in a wire?

A force of 50 newtons acts to move an object 2.5m. What is the work done by the force on the object?

From this more general way of thinking we can jump across to other areas of physics. The only thing that changes is how we come up with the value of the force. In the case of ponies and mines we use weight, a force equal to the mass x the pull of Earth’s gravity. In a different situation the force could be due to electromagnetism, gas pressure, radiation pressure, pretty much anything that can exert a force and cause a movement.

 

Electrical Work Done

Electrical work done, or electrical work for short, is the work done by an electric field on a charged particle which causes the particle to move.

The electrical field in a circuit is produced by the battery. Inside the battery charges separate out towards a positive terminal and a negative terminal. This separation of charge results in an electric field between the positive and negative charges, just like the magnetic field between the north and south poles of a magnet. The electrical field fills the space between the two terminals. To make use of this electric field hold it in a loop of conductive wire. This is a circuit.

This electrical field does work on the free electrons in the conductive metal wire. The electrons move as a result and this average drift of the electrons along the wire is what we call current.

Electrical work done = force from electric field x distance charge moves

In this way chemical energy that was stored inside the battery is reduced and the kinetic energy of the electrons in the wire is increased as work is done on them through the action of the field. This is how batteries run out. Eventually the battery exhausts the chemicals inside it and not enough charges can be separated out to maintain a strong enough electrical field to exert a force on electrons in the wire.

An electric field due to a battery exerts a force of 6×10^-18 newtons on an electron in a 30cm wire. There are 2.5×10^28 free electrons in the wire, what is the total work done to move all these electrons through the wire?

 

Thermodynamic Work Done

There was a famous experiment done by the British scientist James Joule which links the work done by a weight moving through a height, to the heat energy gained by some water. It is regarded as one of the starting points of a whole branch of physics, thermodynamics. Thermo for heat energy and dynamics for how heat is exchanged between systems and their surroundings.

James Joule heat engine

The apparatus used by Joule in his famous experiment

The apparatus is ingenious. By rotating the paddle and transferring energy to the water through friction, Joule was planning to measure the heat energy gained by the water. I always find this astonishing. When I first learnt physics, I had no idea agitating water would heat it up! I always thought of stirring things to cool them down but that is a different process (evaporation) altogether.

Joule figured out that linking the rotating axis of the paddle to a string and pulley system  meant he could lift a weight up at the same time as rotating the paddle. He slowly wound the weight up high, let the system settle and then released the weight. As it dropped, it rapidly turned the paddle and the thermometer reading went up. He was relating an increase in temperature to the work done moving a mass.

Work done to lift weight = energy needed to rotate paddle = energy gained by water

Joule used this to define the mechanical equivalent of heat. Now any change in temperature of a system could be given a number relating it to work done. Work could be done to a system or by a system. This was fantastically useful in the time of steam engines, with their hot boiler tanks, pressurised gases pushing mechanical parts around causing motion.

When we use the word “system” in physics we mean whatever object or objects are being affected. It could be a boiler filled with water turning into steam. The entire thing, container, liquid and gas would be the system. Energy would be supplied to the system through a fire heating the boiler. It would be transferred out of the system through heat loss and the steam escaping to push a turbine or piston.

Work done in thermodynamics is the energy transferred by a hot system to its surroundings. The amount of work done by this system is found from the effect it has on its surroundings. So if a system of hot gas expands and pushes on a piston the work done is defined by the movement of the piston caused by an expansion of the gas.

heat transferred into a system = work done on surroundings + heat left in the system 

Concluding Work Done

Work is such a useful and big concept. We have barely scratched the surface here. The main points to take away are

  • Work done is a way of transferring energy from one store to another.
  • As a sort of energy in flux, it is also measured in Joules.
  • Work always gets things moving, its results in an increase in kinetic energy of something.
  • It doesn’t matter what sort of force is acting, so long as it makes something move.
  • The movement can be as general as the pressure of a gas pushing on its surroundings.
  • All calculations of work done reduce to force acting x distance moved.

 

Answers to Questions

A horse hauls 500kg up a 20m mine shaft. What is the work done by the horse on the load? (take g = 10 m/s^2)

Work done = force x distance, force in this case is a weight of 500x10N = 5000N using the relationship weight = mass x g. 

Thus work done = 5000N x 20m = 100,000J

A barge horse is pulling barge with an effective mass of 8000 lb along a river for 1km. 1kg = 2.2lbs. Covert the weight to kgs and calculate the work done by the horse on the barge.

The effective mass is how heavy it feels to the horse to pull barge probably weighing tonnes along in water. The horse isn’t actually lifting the barge up so this isn’t the actual mass of the barge.

Force of barge in N = effective mass in kg x g = 8000 x 2.2 x 10 = 176,000

Work done = force (N) x distance (m) = 8000x 2.2 x 10 x 1000 = 1.76 x 10^8J

A steam engine can do the work of 4 horses. One horse can move 600kg a distance of 3km in 1 hour. How much work can each horse do? How much work does the engine do in 1 hour? What is the power (joules per second) of the steam engine?

One horse can do 600 x 10 x 3000 = 18,000,000J of work.

The engine does 4 x work of one horse = 4 x 18,000,000J = 72,000,000J in one hour

power = energy (J) / time (s) = 72,000,000 / (60×60) = 2000W

A force of 50 newtons acts to move an object 2.5m. What is the work done by the force on the object?

work done = force x distance = 50N x 2.5m = 125J

An electric field due to a battery exerts a force of 6×10^-18 newtons on an electron in a 30cm wire. There are 2.5×10^28 free electrons in the wire, what is the total work done to move all these electrons through the wire?

work done = force on one electron x length of wire x number of electrons

work done = 6×10^-18 x 0.3 x 2.5x 10^28 = 4.5 x 10^10 J

 

Hubble’s Law – Using Historical Data 1

When teaching physics I think there is a lot of reliance upon writing down a law, Hubble’s Law for example, on the blackboard at the start of a lesson. Then without much or indeed any explanation as to how this result came about, students are left to to work out some example problems or do a couple of experiments using this result.  They are expected to accept without question the “Law of Physics” we have given them. This doesn’t encourage critical thinking and this approach is one of the reasons so many students are turned off physics as a subject.

Chalk and talk teaching is unhelpful and frankly boring. A better way to teach is to supply information and allow the students to discover the results for themselves. Not only is this more interesting, but by doing the work themselves the students learn more effectively and this method mimics the actual scientific process of discovery and deduction. Now I appreciate we don’t have access to large telescopes and apparatus, I’m not suggesting we reproduce the entire experiment! We can make use of historical data to enable students to reproduce important results for themselves. I’m going to write a few posts which show how the data from various famous experiments can be used when teaching physics.

Teaching Hubble’s Law

 

Hubble’s Law describes the expansion of spacetime

Hubble’s Law is an example of a topic which can be taught this way. Usually it is taught by stating the relationship between distance and recessional velocity (Hubble’s Law V=Hr) and this equation is used to deduce the age of the universe etc. Some discussion is made of the interpretation of the recessional velocity – students are expected to understand that spacetime itself is expanding between the observer on Earth and the distant galaxy not that all galaxies are flying away from us.

So turn the lesson around and start with the data. Hubble’s original research paper is short and the data produces a nice line graph. Students can be given the data and be tasked with reproducing his graph of results. They can then construct their own interpretation of what the linear relationship implies. It is good practice to get students to label their graphs with a sentence or two describing the data for example: “a graph to show the relationship between recessional velocity of galaxies and the distance to those galaxies”. Teasing out precisely what relationship; linear, inversely proportional or whatever, can follow.  Students can find a value for the Hubble constant from the gradient of their line of best fit. Comparing this to present day values shows the considerable advances in our measurements of redshifts and distances.

A little bit of algebraic manipulation draws out the units for the Hubble constant as being per unit of time. Time from what? is the key question to ask. What is the start time and what is the end time to find the difference in times that go with the difference in distance to give us a velocity? Change in distance/change in time = velocity. Every time I have taught this one student at least realises that 1/Ho is the time since the galaxies started to move apart and is therefor an estimate for the age of the Universe. You don’t have to tell them, they can work it out! This starts all sorts of discussion about how appropriate this estimate of the age of the Universe is. It is a great way to introduce the earlier, hotter, radiation dominated phase of the Universe where the rate of expansion was slightly different and then further back to Inflation and the Hot Big Bang Theory.

Active learning, the idea that students are working out the relationships not being passive recipients of them as Laws of Physics, has been shown time and time again to produce better learning outcomes. Students understand the topics better and recall more of the information correctly when assessed.

Here is a worksheet which allows more able GCSE 14-16 year olds or AS/A2 16-18 year olds to plot Hubble’s data. A scientific calculator is required and this activity wouldn’t be suitable for students who struggle with large numbers or data processing.

I have also attached Hubble’s paper “A Relation Between Distance and Radial Velocity Among Extra Galactic Nebulae” from 1929.

Equipment needed: graph paper, rulers, pencils and scientific calculators or log tables.

A RELATION BETWEEN DISTANCE AND RADIAL VELOCITY AMONG EXTRA-GALACTIC NEBULAE by Edwin Hubble

Hubble’s Law worksheet

The Great American Eclipse – critical thinking resource

Critical thinking is such an important skill and a fundamental tool in science. We do not believe, we prove beyond reasonable doubt. Increasingly inaccurate, deliberately false and manipulative information is being shared on social media and it becomes vital that our students and ourselves can think critically about what we are seeing. Just because it is on the internet doesn’t make it fact, even if lots of other people have “liked” it. Here I unpick a particular example from earlier this year which nearly tripped me up.

You can’t have missed the fact that a total solar eclipse tracked from sea to shining sea in the USA on 21st August 2017. There were some beautiful images posted of dramatic darkened skies. One in particular popped up on my social media timeline which at first glance was an impressive, nay even stunning image.

My first impression was followed by a jarring feeling of incongruity, something about this felt off. I have painted pictures of a moon over the sea and I know the sun and moon appear similar in size in the sky, that’s why eclipses happen after all. The sun-moon seemed a bit too big compared to the size of the waves, to the distance to the horizon. Then I clocked how bright it is, totality during an eclipse is so dark you can see the stars. Then I spotted the clouds appeared behind the sun-moon and finally every photo of the sun at the horizon I have ever seen shows visual distortion due to the much thicker atmosphere, like this one here;

yet the faked image shows a perfect circle just touching the sea. It looks beautiful but is completely fake, a quick google search revealed the height of the sun over the coast of  Oregon at totality was actually much higher and at 10.15am in the morning. So I call bullshit on this image.

Fake news is an increasingly common topic of discussion amongst people concerned by the way deliberate bias and propaganda or plain ignorance is infiltrating all of our contact with news and information online.In the UK the government curriculum changes in the sciences were designed to increase scientific literacy in students by exposing them to topics deemed contentious by the media like GMOs, mobile phone radiation risk, use of vaccines and training the students to question the sources and reliability of the data used to back up outlandish claims against scientific advice.

One of the most beneficial aspects of studying science is of course the development of critical thinking skills. This faked image is a great way to engage students in this key skill.

Activity – Critical Thinking

Display the faked image (search faked eclipse photos) and its attribution (Oregon, USA) and ask the students do they believe it is real and why, is there anything a bit off about it, where is Oregon on a map and which way does the Earth rotate, and how could they check the veracity of the claim.

Follow up discussion can explore phenomena such as the distortion of the sun at the horizon, the light levels at totality, the size of the sun and moon in the sky etc.

A selection of faked and real photos could then be put up with students voting on which they think is real and why.

Follow-up activities:

Homework on an aspect of the discussion such as the mechanics of an eclipse and the relative sizes of the sun and moon in the sky, or following on with critical thinking skills a single side of writing on “how to spot fake eclipse photos”.