Energy, waves and electricity for high-school physics: study cards over three tiers, the tricky ones, a practice quiz at three levels — Foundation, On-Level, and Challenge — and a lab where you label a circuit diagram, graph Ohm's law for one resistor and read its resistance off the slope, sort twelve circuit facts series or parallel, and argue from a ramp, a photogate and a thermometer where 22.8 missing joules went. Work here, or print it and use a pencil — both count.
One resistor across a battery. There is one path for the current to take.
Adding a branch in parallel LOWERS the total resistance, because it is a wider pipe and not a longer one. Series: same current everywhere, voltages add. Parallel: same voltage everywhere, currents add.
What people get wrong
⚠️People often think…
Holding a heavy bag still is hard work, so you are doing work on it.
Work in physics needs DISTANCE along the force. The bag does not move, so the work on it is exactly zero — and carrying it level is zero too, since the force is up and the motion is sideways. Your muscles are burning energy; the bag is not receiving any.
No distance along the force, no work.
⚠️People often think…
Friction destroys energy — that is why the total does not add up.
It always adds up. Friction converts the missing kinetic energy into HEAT, joule for joule. Measure the temperature rise of the brake and the surface and you will find every one of them.
Friction makes heat. The ledger balances.
⚠️People often think…
Light slowing down in glass changes its color.
Refraction changes SPEED and wavelength, never frequency — and frequency is what your eye reads as color. Red light underwater is still red. That is also why a prism bends colors by different amounts without recoloring them.
Frequency survives. Color survives with it.
⚠️People often think…
A kilowatt and a kilowatt-hour are two ways of saying the same amount.
A kilowatt is a RATE — how fast energy is being used. A kilowatt-hour is an AMOUNT, 3.6 million joules. It is the difference between miles per hour and miles, and your electric bill charges you for the second one.
Watt is a rate. Watt-hour is an amount.
Ledger, waves, circuits
1Watch one
Two identical bulbs in series, then the same two in parallel. Which pair is brighter?
In series the resistances add, so the total goes UP and the current drops.
In parallel you added a path, so the total goes DOWN and more current flows.
Each parallel bulb also gets the FULL battery voltage; the series bulbs split it.
Parallel is brighter — which is why house wiring is parallel, so one lamp does not dim the rest. ✓
2Do one with me
Fill in the ledger and the circuit.
Work done on a bag you hold still is
Adding a branch in parallel makes total resistance go
Refraction never changes a wave’s
💬One sentence, then you move on
Why does adding a parallel branch lower the resistance?
3Try one
In a series circuit, which resistor heats up the most?
I want a hint first
Heating is I²R. In series, I is the same in every component. So what is left to vary?
💬Last one — then you're done here
Why is a kilowatt-hour on your bill and not a kilowatt?
Where this goes
Where this lives
Why houses are wired in parallel, why an extension cord gets warm, why a straw looks bent in a glass, what the number on your electric bill is actually counting.
What this feeds
Next unit is environmental science, where these numbers get applied to whole systems.
Name one appliance whose wattage you have seen printed on it.
One card at a time — tap “Show me” to check yourself, then Next. Start at Foundation; when those feel easy, climb.
Helpful Hints
🪜 Energy, waves, electricity — the ladder
Work transfers energy, W = Fd cos θ, and net work is the change in kinetic energy → potential energy (mgh, ½kx²) and heat complete the ledger, and the total never changes → power is the rate → waves add point by point: constructive, destructive, standing; sound and light both interfere, diffract and Doppler-shift → charge follows an inverse-square law → V = IR and P = IV run every circuit; series shares current, parallel shares voltage → moving charge makes magnetism, moving magnetism makes current, and that is every motor and generator.
Keep the ledger; add the waves; solve the circuit; spin the coil.
🤝 The whole idea
Three conservation-style rules run this unit: energy is never lost, only moved; waves pass through each other, adding as they go; and in a circuit what goes in at the battery comes out as heat and light somewhere, exactly.
Nothing is lost. Everything is somewhere.
⚠️ Tricky ones
Work needs distance ALONG the force. Holding a heavy bag still, or carrying it level, is zero work on the bag.
Friction doesn’t destroy energy. It makes heat, and the heat equals the missing joules exactly.
Power is a RATE. A kilowatt-hour is energy (3.6 MJ); a kilowatt is how fast.
Refraction changes SPEED and wavelength, never frequency — the color stays.
Series: same CURRENT, voltages add. Parallel: same VOLTAGE, currents add. Don’t swap them.
Adding a parallel branch LOWERS total resistance. It is a wider pipe, not a longer one.
A wire heats by I²R. Same current everywhere in series, so the biggest resistance takes the heat.
🔌 Series versus parallel — the chart
Series (one path)
Parallel (several paths)
current
the same through every part
splits among branches, adds back up
voltage
splits in proportion to resistance
the same across every branch
total resistance
R = R₁ + R₂ + …
1/R = 1/R₁ + 1/R₂ + …
add a component
resistance rises, current falls
resistance falls, current rises
one part fails
everything stops
the rest keep running
worked: 12 V, 2 Ω and 4 Ω
6 Ω · 2 A · 4 V and 8 V
1.33 Ω · 6 A + 3 A = 9 A · 12 V each
Your house is parallel. A string of old holiday lights was series.
🎯 How the test will ask
“A block slides down a ramp of height h and arrives at speed v. How much energy went to friction?”
“Find the minimum speed at the top of a loop of radius r.”
A standing wave sketched with three loops — “find the wavelength and frequency.”
A circuit diagram — “find the total resistance, the current from the battery, and the voltage across each resistor.”
An I–V graph with two lines — “which is ohmic? which has more resistance?”
“Explain how a generator produces current, and why it is a motor in reverse.”
✅ Can you…
Do the energy ledger with friction and find the heat?
Find power from work and time, or from I and V?
Predict interference, and read a standing wave for its wavelength?
Explain refraction and the two-slit pattern as wave behavior?
Solve a mixed series–parallel circuit and check that the power adds up?
Explain induction, and why a motor run backward is a generator?
Pick your level
Look back at anything you missed — the hint that appeared is exactly what to reread tonight.
How sure did you feel?
Lab
Work like a scientist: label the diagrams, turn the table into a graph, then write a claim with evidence and reasoning. Every lab checks itself on the spot, and hints are free.
Your practice never leaves this device. There is no account and no sign-in. Your work is saved in this browser only, and you can erase it whenever you want.
Your practice record — saved on this device
This is your record of the module on screen — it stays here and goes nowhere. Independent means you got it right on the first tap; supported means you got it after the explain-and-retry, or marked ‘I had it’ on a revealed answer. Both count, and neither is a grade. If your teacher asks, copy the row or show them this screen.
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The answer key is for a teacher: it prints only from here, for the unit on screen. Print the study packet prints the study pages and a blank quiz — never the answers.