A  P H Y S I C S   L E S S O N
Electricity:
Current, Conductors
& Circuits
What really happens inside the wires when you switch on a lamp?
+  →  lamp  →  −
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CHAPTER 1   ELECTRIC CURRENT
Tiny Travellers: Electrons
An electric current is a flow of electric charge along a path.
  • Everything is made of atoms. Around each atom whizz even tinier particles called electrons.
  • Electrons carry a negative electric charge (−).
  • In a metal wire, some electrons are free: they can hop from atom to atom.
  • When a battery pushes them all along the wire, they make an electric current.
Measuring current
Current is measured in amperes (A). A phone charger gives about 2 A.
Inside a copper wire +++++ ++++ free electron (−) copper atom (stays put)
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CHAPTER 1   ELECTRIC CURRENT
Think of Water in Pipes
Electricity is invisible, but it behaves a bit like water flowing in a loop of pipes.
+

B A T T E R Y

= the pump

It pushes the charges around. How hard it pushes is its voltage, in volts (V).

⎯

W I R E

= the pipe

It gives the charges a path to follow, all the way around and back.

→

C U R R E N T

= the flow

How much charge passes each second, in amperes (A).

●

L A M P

= the water wheel

It uses the energy of the flow, here to make light and heat.

No pump, no flow. A broken pipe, no flow. Electricity is the same!
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CHAPTER 1   ELECTRIC CURRENT
A Circuit Is a Loop
Current only flows when there is a complete path from one end of the battery back to the other.
+− switch closed

CLOSED CIRCUIT — LAMP ON

The loop is complete: current flows all the way round.

+− switch open

OPEN CIRCUIT — LAMP OFF

A switch opens a gap. The path is broken, so nothing flows anywhere.

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CHAPTER 2   CONDUCTORS & INSULATORS
Conductors and Insulators
Some materials let current through. Others stop it dead.

C O N D U C T O R S

Let electric current flow through them.

  • copper (inside cables)
  • aluminium (foil, cans)
  • steel (paper clips, spoons)
  • gold (computer connectors)
  • graphite (pencil lead)
  • salt water — and your body!

I N S U L A T O R S

Block electric current.

  • plastic (cable coating, toys)
  • rubber (boots, gloves)
  • glass (windows, bottles)
  • dry wood
  • ceramic (plates, mugs)
  • air, paper, fabric
Why? In conductors, electrons are free to move. In insulators, they are held tightly by their atoms.
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CHAPTER 2   CONDUCTORS & INSULATORS
A Team: Copper Inside, Plastic Outside
plastic: insulator keeps the current in copper: conductor carries the current

Every electric cable uses both: a conductor to guide the current, and an insulator wrapped around it so the current can't escape into you.

Surprising conductors
Graphite, the grey "lead" in a pencil, is not a metal, but it conducts!
Tap water and salt water conduct too, and so does the human body, which is full of salty water.
That's why…
you must never touch switches or sockets with wet hands, or use a hair-dryer near the bath. Air is an insulator… until lightning is strong enough to jump right through it!
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CHAPTER 3   THE DIRECTION OF CURRENT
Which Way Does It Flow?
+ → lamp → −
Outside the battery, electric current flows out of the + terminal, around the circuit, and back into the − terminal.
Inside the battery, it is pushed back from − to +, ready for another lap.
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CHAPTER 3   THE DIRECTION OF CURRENT
A Mix-up From History
  • Around 1750, Benjamin Franklin guessed that electricity flows from + to −. Everybody followed his choice.
  • In 1897, J. J. Thomson discovered the electron… and electrons are negative, so they really travel the other way: from − to +!
  • Scientists kept Franklin's rule anyway. So today:

CURRENT

drawn from + to −

ELECTRONS

move from − to +

+− current electrons
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CHAPTER 3   THE DIRECTION OF CURRENT
When the Direction Matters
A lamp works both ways round. Some parts don't!

D I O D E

A one-way street for current. It only lets current pass in the direction of its arrow, and blocks it the other way.

L E D

A diode that lights up. Its long leg goes to +. Put it in backwards and it stays dark.

B A T T E R I E S

Look for the + and − marks in the battery box of your toys. The wrong way round, the toy won't work.

In the Circuit Maze game, diodes will only let the current through if they point from A (+) towards B (−).
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CHAPTER 4   BUILDING CIRCUITS
Drawing Circuits Like a Scientist
Instead of drawing real objects, we use simple symbols everybody understands.
Wire
a path for current
Battery
long line = +
Lamp
lights up
Motor
turns and moves
Resistor
slows the current
Open switch
gap: no current
Closed switch
current flows
Diode
one way only
LED
a diode that shines
Europe
America
Resistor: two ways to draw it
A resistor makes it harder for the current to flow, like a narrow part in a water pipe. More resistance means less current: a lamp in series with a resistor shines more dimly. Lamps and motors resist the current too.
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CHAPTER 4   BUILDING CIRCUITS
Series Circuit: One Single Path
+− lamps one after the other
  • The parts are connected one after the other, like wagons behind a train.
  • There is only one path, so the same current flows through every lamp.
  • The lamps share the battery's push: with two lamps, each one is dimmer.
  • If one lamp breaks, the loop is open and all the lamps go out.
Where you find it
Old Christmas lights: one dead bulb and the whole string went dark! Batteries stacked in a torch are in series too.
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CHAPTER 4   BUILDING CIRCUITS
Parallel Circuit: Several Paths
+− each lamp on its own branch
  • The current splits into several branches, then joins up again before going back to the battery.
  • Each lamp gets the full push of the battery, so each shines brightly.
  • If one lamp breaks, the other branch is still a complete loop: the other lamps stay on.
  • But more current leaves the battery, so it runs out faster.
Where you find it
In your house! Every lamp and socket is in parallel, so switching off the kitchen light doesn't switch off the fridge.
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CHAPTER 4   BUILDING CIRCUITS
Series or Parallel?
SeriesParallel
Paths for the currentOnly oneSeveral branches
CurrentThe same everywhere in the loopSplits between the branches, then joins again
Two lampsBoth dimmer: they share the pushBoth bright: each gets the full push
One lamp breaksEverything goes outThe others keep shining
ExamplesOld Christmas lights, batteries in a torchLights and sockets in a house
Many real circuits mix both: some parts in series, others in parallel.
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CHAPTER 5   STAY SAFE
Short Circuits and Safety
+− HOT! lamp skipped: off

A short circuit is an easy shortcut that skips the lamp. A huge current rushes through, the wires get hot, and batteries can leak or even catch fire.

Golden rules
  • Only experiment with small batteries (1.5 V to 9 V).
  • Never poke anything into a wall socket: its 230 V can kill.
  • Keep electricity away from water, and never touch a switch with wet hands.
  • Stay far from power lines and substations, and never fly a kite near them.
  • Never join the + and − of a battery with just a wire.
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T H R E E   B I G   I D E A S
What You've Learned
1
Conductors & insulators

Metals and graphite let current through. Plastic, rubber, glass and wood block it.

2
Current flows + → −

Around a complete loop. Electrons go the other way. Diodes care about direction!

3
Series or parallel

One path: lamps share the push. Several paths: each lamp gets it all.

Play the Circuit Maze! Play Lamp Detective!
⚡ Meet Étienne: a real circuit on rails
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