Seeing the Invisible – Electrons in a Cathode Ray Tube

Electrons… tiny, negatively charged particles that you can’t see, touch, or smell.

Yet in the lab, we can make them visible.

One of my favourite demonstrations (and a classic in physics) is using a Cathode Ray Tube (CRT) to “see” electrons in action. It’s a beautiful mix of theory and real-world evidence.

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What is a Cathode Ray Tube?

A CRT is essentially a vacuum tube with three key parts:

• Electron gun – fires electrons from a heated cathode
• Deflection plates – control the path of the electrons
• Fluorescent screen – glows when struck by electrons

In a vacuum, electrons travel in straight lines. When they hit the screen, they produce a glowing spot — suddenly, the invisible becomes visible.

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What Does This Show Us About Electrons?

This simple setup reveals some fundamental properties of electrons:

1. Electrons have mass

They travel in straight lines and can be deflected. Anything that changes direction must have mass.

2. Electrons carry negative charge

Apply an electric field across the plates and the beam bends toward the positive plate. That tells us the charge is negative.

3. Electrons can be accelerated

By increasing the voltage, the beam moves faster and hits the screen with more energy.

4. Electrons behave predictably

They follow well-defined paths under electric and magnetic fields — essential for understanding circuits and modern electronics.

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The Key Experiment

This work traces back to J. J. Thomson in 1897, who used a CRT to measure the charge-to-mass ratio of the electron.

His conclusion?
Atoms were not indivisible after all.

That discovery completely changed physics.

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Why This Still Matters Today

CRT technology may feel old-fashioned (unless you’ve still got an ancient TV in the loft), but the principles are everywhere:

• Oscilloscopes in school labs
• Electron microscopes
• Particle accelerators
• Even the foundations of modern electronics

And more importantly for students:

👉 It’s a perfect exam topic – linking electricity, fields, and particle physics in one neat experiment.

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A Classroom Twist

When I run this demonstration, I often ask students:

“Are we actually seeing electrons… or just the effect of electrons?”

It’s a great way to push thinking beyond memorising facts and into understanding evidence.

Exploring Electron Properties with Teltron Tubes

There’s something rather magical about switching on a Teltron tube in a darkened lab…

A faint green glow appears… then a beam… and suddenly you are watching electrons move in real time.

For students, this is often the moment when abstract physics becomes real.

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What Are Teltron Tubes?

Teltron tubes are modern versions of the classic cathode ray experiments. They allow us to investigate electrons under controlled conditions with much clearer visual results than older equipment.

Typically, they include:

• A low-pressure gas-filled tube (so the electron path glows)
• An electron gun to produce a beam
• Electric and/or magnetic field controls
• Often Helmholtz coils to create a uniform magnetic field

The result? A visible beam of electrons that we can bend, shape, and measure.

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What Can We Learn?

Using Teltron tubes, students can explore several key properties of electrons:

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1. Electrons Travel in Straight Lines

With no external fields applied, the beam travels directly from the cathode to the screen.

Evidence that electrons behave like particles with momentum.

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2. Electrons Carry Charge

Apply an electric field and the beam deflects.

Just like in the experiments of J. J. Thomson, the direction of deflection shows the electron is negatively charged.

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3. Magnetic Fields Curve Electron Paths

Switch on the Helmholtz coils and something wonderful happens…

The straight beam becomes a circle.

That circular motion is caused by the magnetic force acting perpendicular to the velocity of the electrons.

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4. Measuring the Charge-to-Mass Ratio

This is where it gets really interesting.

By adjusting the magnetic field and measuring the radius of the circular path, students can calculate the specific charge (e/m) of the electron.

The relationship is:

$\frac{e}{m} = \frac{v}{Br}$

(Combined with energy from accelerating voltage in full derivations.)

This is not just theory — this is a real experimental measurement of a fundamental constant.

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Why Teltron Tubes Are Brilliant for Teaching

From years of teaching, these are a few reasons they work so well:

• Students can see the beam move instantly
• Adjusting controls gives immediate feedback
• It links multiple topics:
  • Electricity
  • Magnetism
  • Circular motion
  • Particle physics

And perhaps most importantly…

It encourages curiosity.

Students start asking:

• “What happens if I increase the voltage?”
• “Why does the circle get bigger?”
• “Can we stop it completely?”

That’s when real learning begins.

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A Classic Demonstration Trick

I often start by asking:

“If electrons are so small… how can we possibly see them?”

Then I switch off the lights and power up the tube.

The reaction is always the same.

A quiet:
“Whoa…”

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Bringing It Back to Exams

Teltron tube experiments regularly underpin exam questions on:

• Magnetic fields and forces
• Circular motion
• Energy and accelerating voltage
• Experimental methods and uncertainties

So while it looks like a bit of fun…

It’s also serious exam preparation.

 Spring Has Sprung – And So Has Photosynthesis!

There’s something magical about spring. The trees burst into leaf, gardens wake up, and suddenly everything is… green again.

But behind that explosion of life is one of the most important biological processes on Earth: photosynthesis.

And at the heart of photosynthesis lie two unsung heroes:
Photosystem I (PSI)
Photosystem II (PSII)

They sound like they should come in order… but, as with many things in biology, it’s not quite that simple.

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The Big Picture

Photosynthesis happens inside chloroplasts, specifically in the thylakoid membranes.

Both photosystems:

• Absorb light energy
• Use chlorophyll
• Drive the light-dependent reactions

But they do very different jobs.

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Photosystem II – The One That Goes First (Despite the Name)

Photosystem II is where it all begins.

Key features:

• Absorbs light best at 680 nm (called P680)
• Splits water (photolysis)
• Produces:
  • Oxygen (O₂) 
  • Protons (H⁺)
  • Electrons (e⁻)

This is why plants produce oxygen – a rather useful by-product for the rest of us!

What it does:

• Boosts electrons to a higher energy level
• Sends them down an electron transport chain
• Helps create a proton gradient → used to make ATP

Think of PSII as the “starter motor” of photosynthesis.

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Photosystem I – The Finisher

Photosystem I comes later in the process.

Key features:

• Absorbs light best at 700 nm (P700)
• Does not split water
• Uses incoming electrons to make NADPH

What it does:

• Re-energises electrons (they’ve lost energy along the chain)
• Transfers them to NADP⁺
• Forms NADPH → essential for the Calvin Cycle

Think of PSI as the “final boost” that stores energy in a usable chemical form.

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The Key Differences (Exam Gold!)

Feature	Photosystem II	Photosystem I
Order	First	Second
Reaction centre	P680	P700
Splits water?	✅ Yes	❌ No
Produces oxygen?	✅ Yes	❌ No
Main role	Electron supply + ATP production	NADPH production
Position	Start of ETC	End of ETC

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🌼 Why This Matters in Spring

All that fresh green growth you see:

• Leaves unfolding
• Grass racing ahead of your lawnmower
• Blossoms appearing almost overnight

It’s powered by PSII and PSI working together

PSII provides:

• The electrons
• The oxygen

PSI provides:

• The reducing power (NADPH)

Together, they allow plants to turn:
Light + Water + CO₂
Into glucose and life itself

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A Quick Teaching Tip (From the Lab)

Students often remember it like this:

“2 before 1”

• Photosystem II happens first
• Photosystem I happens second

It’s counterintuitive… which is exactly why examiners love it.

 From Split Brains to Taxi Drivers: Learning How the Brain Works

The human brain is a wonderfully awkward thing. It lets us write essays, drive cars, remember where we left the keys, and occasionally walk into a room with absolutely no idea why we went there in the first place.

In psychology, one of the most fascinating things is that we have learnt so much about how the brain works not just by looking at healthy brains, but by studying what happens when something changes, gets damaged, or develops in an unusual way. In other words, psychology has often progressed by looking at brains under pressure.

Take the famous split-brain studies by Roger Sperry. These involved people whose two brain hemispheres had been surgically separated to reduce severe epilepsy. Suddenly, psychologists had a way to explore what each half of the brain was doing. What they found was extraordinary. The left and right hemispheres could process information differently, and in some cases seemed almost like two minds sharing the same skull. It was a dramatic reminder that the brain is not just one simple lump doing everything together. It is specialised, divided, and yet somehow usually works as a whole.

Then there is the case of HM, one of the most important patients in psychology. After surgery intended to help his epilepsy, he could no longer form new long-term memories. He could remember much of his earlier life, but new experiences slipped away almost immediately. From this tragic case, psychologists learnt a huge amount about memory. We discovered that memory is not a single system. There are different types of memory, handled by different brain structures, and the hippocampus is especially important for forming new long-term memories.

And then we come to one of my favourites: London taxi drivers. You might think they belong in a transport blog rather than a psychology one, but they helped reveal something very important about the brain. To qualify as a London taxi driver, people traditionally had to learn “The Knowledge” — an astonishing mental map of London streets and routes. Studies found differences in the hippocampus of these taxi drivers compared with other people. In simple terms, the brain appeared to adapt to the demands placed on it. The more it was used for spatial navigation, the more it changed. That is a powerful example of neuroplasticity — the brain’s ability to reorganise itself.

So what do split brains, memory patients, and taxi drivers all have in common?

They show that the brain is both specialised and adaptable.

Some parts of the brain are linked with particular functions. Language tends to be strongly associated with the left hemisphere in most people. Memory formation relies heavily on the hippocampus. Spatial navigation can reshape parts of the brain through repeated use. But at the same time, the brain is not rigid. It changes with experience. It responds to injury, training, learning, and environment.

That matters far beyond the psychology classroom.

It matters for education, because repetition and practice really do help build pathways in the brain.

It matters for rehabilitation, because people can sometimes recover lost skills or find new ways around damaged areas.

It matters for ageing, because keeping the brain active is not just a nice slogan. It has a biological basis.

And it matters for students, because psychology is not just about theories on a page. It is about real people, real brains, and real evidence.

What I like about this topic is that it brings psychology alive. You start with a textbook term like localisation of function or neuroplasticity, and then suddenly you are talking about a man who cannot form new memories, people whose hemispheres no longer communicate normally, or taxi drivers whose brains have adapted to the roads of London.

That is when psychology stops being a list of names and studies and starts becoming a story about what makes us human.

The brain is not a finished machine that comes out of the box complete. It is more like an ongoing building project — part wiring diagram, part road map, part improvisation. Most of the time it works brilliantly. Sometimes it gets things wrong. And sometimes, by studying those mistakes and changes, we learn the most.

So yes, from split brains to taxi drivers, psychology gives us an extraordinary window into how the brain works.

And if you have forgotten where you put your glasses while reading this, do not worry. Your hippocampus is probably doing its best.

Analogue Computers Aren’t Dead — They’re Just Evolving

When most people hear the words computer, they picture something digital: a laptop, a phone, a tablet, or perhaps a powerful server farm humming away in a data centre. Everything today seems to come down to bits, binary, and software.

So surely analog computers are dead?

Not at all.

They have simply slipped quietly out of the spotlight and changed form.

Long before digital machines took over, analog computers were solving problems by using physical quantities to represent other quantities. A voltage might stand for speed. A rotating shaft might stand for time. The movement of gears, wheels, pulleys, fluids or electrical currents could model a real system directly. Rather than calculating with ones and zeros, an analog computer behaved like the problem.

That is what made them so clever.

A slide rule is a simple analog computer. So is a car’s old-fashioned speedometer. A mechanical tide predictor, a differential analyser, and even some flight instruments all used continuous physical change to model a system and give an answer.

Digital computers eventually pushed most analog machines aside because they are more flexible, more precise in many situations, easier to programme, and much better at storing and copying information. One machine can do thousands of completely different jobs just by loading different software. That is hard to beat.

But analog never completely vanished.

In fact, it is having something of a quiet comeback.

One reason is speed. For some specialised tasks, analog systems can process information in real time with extraordinary efficiency because they are not simulating the system step by step — they are the system in electrical form. This can be useful in control systems, signal processing, and some kinds of scientific instrumentation.

Another reason is energy use. As we push against the limits of power consumption in modern computing, researchers are once again asking whether certain tasks can be handled more efficiently by analog or hybrid analog-digital designs. It turns out that using a continuous physical system to solve a continuous physical problem is sometimes rather sensible.

Then there is artificial intelligence. Much of the excitement today is about digital AI running on powerful chips, but researchers are also exploring analog approaches in neuromorphic computing, optical computing, and in-memory computing. These systems try to do some of the work in a way that is closer to how nature works: parallel, continuous, and efficient.

Even the humble sensor is often analog at heart. Temperature, light, sound, pressure and motion all begin life as analog signals. Before a digital system can process them, they often need to be measured, amplified, filtered or converted. The digital world still rests heavily on analog foundations.

So no, analog computers are not dead.

They are just no longer sitting in the middle of the desk with spinning discs and dramatic levers. They are hidden inside modern systems, reborn in specialist hardware, and reappearing in research labs where engineers are trying to solve problems that digital machines do not handle efficiently enough on their own.

In a way, analog computing has grown up.

It no longer tries to be the universal machine that digital computing became. Instead, it is finding its place as the smart specialist — fast, elegant, efficient, and sometimes far better suited to the job.

Which is a useful lesson in itself. In technology, old ideas rarely die completely. They just wait for the right moment to return wearing a new jacket.

And probably with fewer cogs.

 

Chemistry Calculations – Easy… Until Rates Appear!

“It Was All Going So Well… Then They Asked for the Rate”

Chemistry calculations are, for the most part, quite friendly.

Moles?
No problem.
Concentration?
Straightforward.
Titrations?
A bit fiddly, but manageable with practice.

Then… along comes rates of reaction.

And suddenly everything feels like it’s been turned upside down.

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What Changes When Rates Appear?

Up until now, most calculations are nice and structured:

• You’re given values
• You follow a formula
• You get an answer

But rates questions introduce something new:

Time

And time complicates everything.

Now you’re not just working out how much —
you’re working out how fast it’s happening.

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The Real Problem: Graphs

This is where most students come unstuck.

You’re given a graph and asked:

• What is the rate at the start?
• What is the rate at 20 seconds?
• How does the rate change over time?

And the dreaded instruction appears:

“Draw a tangent…”

At this point, confidence often disappears.

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Why Students Struggle

It’s not actually the chemistry — it’s the maths skills inside the chemistry.

Students need to:

• Understand gradients (slopes)
• Draw a tangent accurately
• Calculate rise/run
• Interpret changing curves

In other words…

It quietly becomes a maths question disguised as chemistry

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What Is Rate (Really)?

At its simplest:

Rate = amount ÷ time

But in chemistry, we refine that idea:

• Rate changes during a reaction
• It’s fastest at the start
• It slows as reactants are used up

So instead of a simple calculation, we often need:

Rate at a specific moment
(which is where the tangent comes in)

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Practical Work Helps (A Lot!)

This is one topic where doing the experiment makes everything clearer.

For example:

• Measuring gas produced using a gas syringe
• Timing how long a reaction takes to cloud
• Watching how quickly bubbles form

Suddenly the graph isn’t abstract anymore — it’s real data you’ve collected.

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Exam Tip (Gold Dust)

When you see a rates question:

1. Read the graph carefully
2. If asked for rate at a point → draw a tangent
3. Make your triangle big (for accuracy)
4. Calculate gradient clearly
5. Include units (students forget this!)

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Final Thought

Chemistry calculations don’t suddenly become hard…

They just quietly turn into maths when you’re not looking.

Master the graph skills, and suddenly:

Rates become one of the easiest topics on the paper.

 

The PASCO Smart Cart – More Than Just a Toy on Wheels

When most students first see the PASCO Smart Cart, they assume it’s just another trolley to push along a track.

“Oh… we’re doing motion again.”

But this little cart is far more than that.

It’s not just about rolling from A to B — it’s a fully equipped mobile physics laboratory.

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Not Just Motion… Proper Physics

Yes, it does motion brilliantly:

• Velocity
• Acceleration
• Graphs in real time

But here’s where it gets interesting…

Students don’t just see motion — they measure it properly, with instant feedback.

No more:

“Sir… I think that line is straight?”

Now we know.

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Forces – Newton Comes Alive

Attach a force sensor and suddenly:

• $F = ma$ isn’t just a formula
• It’s a graph students create themselves

Pull the cart… and watch:

• Force change
• Acceleration respond
• Graphs update instantly

That “aha” moment?
That’s where learning happens.

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Simple Harmonic Motion (Without the Headache)

Hook it to a spring and suddenly SHM becomes:

• Visual
• Measurable
• Understandable

Students can see:

• Displacement
• Velocity
• Acceleration

All at once.

Even better… they can see the phase differences.

(Which normally takes about three lessons and a mild headache to explain.)

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Real Data – Real Understanding

This is the real power of the Smart Cart.

Students:

• Collect their own data
• Analyse it instantly
• Make mistakes
• Fix them

It turns physics from:

“Copy this from the board…”

Into:

“Let’s prove it.”

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Why It Matters

In exams, students are expected to:

• Interpret graphs
• Understand relationships
• Apply knowledge

The Smart Cart trains the students in all of that — without them even realising.

It’s learning by doing.

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Final Thought

Of course… there is one small problem.

Give students a Smart Cart and within 30 seconds someone will ask:

“Can we crash it into the wall?”

Well… yes.

But only in the name of science.

 

Circles, Tangents and Chords – Why the Panic?

There’s something about circles that seems to trigger instant fear in students.

Mention tangents, chords, or anything involving angles in a circle… and suddenly even confident GCSE (and A Level) students start to panic.

But here’s the truth:

These problems are not harder than anything else in maths.
They just look unfamiliar.

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What Are We Actually Dealing With?

At GCSE level, circle questions usually boil down to a small set of rules:

1. Radius ⟂ Tangent

The radius meets the tangent at 90°.

This is your entry point into most problems.

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2. Angles in the Same Segment Are Equal

If two angles sit on the same arc, they are identical.

Spot the arc → match the angles → easy marks.

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3. Angle at Centre = 2 × Angle at Circumference

The angle in the middle is double the one at the edge.

This one appears again and again. Sometimes the top angle slips right round but it is still the same problem.

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4. Cyclic Quadrilateral = 180°

Opposite angles add up to 180°.

A favourite exam trick.

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So Why Do Students Struggle?

It’s not the maths.

It’s the recognition.

Students often:

• Don’t spot which rule to use
• Panic when the diagram looks messy
• Forget that it’s just basic angle rules in disguise

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My Top Tip (After 40 Years Teaching)

Circle the circle rules before you start solving.

Literally.

Look at the diagram and ask:

• Where is the tangent?
• Where is the centre?
• Which angles sit on the same arc?

Then apply one rule at a time.

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The Big Realisation

Once you see it:

Circle questions are just geometry puzzles with a small toolkit

Not scary. Not magical. Just structured.

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A Bit of Honesty…

Students often say:

“I hate circle theorems.”

What they really mean is:

“I haven’t practised enough of them yet.”

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Final Thought

If you practise these regularly, something interesting happens:

You start spotting the answers almost immediately

And that’s when circles go from:
confusing →  satisfying