Electric Charge & Current
From Static Shock to Flowing Electrons
🎈1. The Hook: Why Does a Balloon Stick to the Wall?
You rub a balloon on your sweater and it sticks to the wall like magic. Your hair stands up. You feel a tiny shock when you touch a door handle. What's happening?
Answer: Electrons are jumping between objects, creating electric charge.
2. Baby Steps: What is Electric Charge?
CORE CONCEPT
Stage 1: All matter is made of atoms. Atoms contain three particles:
- Protons (+) positive charge, in the nucleus, CANNOT move
- Neutrons (0) no charge, in the nucleus
- Electrons (-) negative charge, orbit the nucleus, CAN move
Stage 2: Normally, atoms are neutral (equal protons and electrons).
Stage 3: When you rub two insulators together (friction), electrons transfer from one to the other.
⚠️ EXAMINER'S TRAP
Students say "positive charge moves" - WRONG! Only electrons (negative) move. Protons are locked in the nucleus.
The Two Laws of Charge:
Like Charges REPEL
(+ pushes +) or (- pushes -)
Unlike Charges ATTRACT
(+ pulls -)
3. Interactive: The Balloon Friction Simulator
Click the button to rub the balloon on the sweater. Watch electrons jump!
Balloon
Neutral
Start rubbing
Sweater
Neutral
4. Conductors vs Insulators
⚡ CONDUCTORS
Materials with free electrons that can move easily.
Examples: Metals (copper, aluminum, gold)
🛡️ INSULATORS
Materials where electrons are bound to atoms.
Examples: Plastic, rubber, glass, wood
📘 SUPPLEMENT TOPIC STARTS HERE
The following sections (Electric Fields, Current) are Supplement content (for Extended tier students).
5. Electric Fields (Supplement)
An electric field is a region where a charged object experiences a force.
⚡ Field Line Rules:
- Field lines point in the direction a positive test charge would move
- Lines go FROM positive (+) TO negative (-)
- Closer lines = Stronger field
- Lines never cross
Toggle Field Pattern:
Radial Field Around Point Charges
🎨 Interactive: Electric Field Drawer
Click on the canvas to place charges. Watch the field lines form!
Click to add charges (max 8)
6. Electric Current (Supplement)
Definition
Electric current is the rate of flow of electric charge.
The Formula Triangle
I = Q / t
I
Current
(Amperes, A)
Q
Charge
(Coulombs, C)
t
Time
(Seconds, s)
⚠️ Two Types of Current Direction
Conventional Current
The direction POSITIVE charges would flow
From + terminal → to - terminal
(This is what we use in circuit diagrams)
Electron Flow
The ACTUAL direction electrons move
From - terminal → to + terminal
(Opposite to conventional current!)
🔬 Interactive: The Current Counter
Adjust the charge and time. Watch the current calculation update!
Current = 5.00 A
10 C ÷ 2 s = 5.00 A
Physical Meaning: If 10 coulombs pass through this wire cross-section every 2 seconds, the current is 5.00 amperes.
⚠️ Master Examiner's Trap List
Trap 1: What moves?
❌ "Positive charges move in friction" → ✅ "Only electrons move"
Trap 2: Field direction
❌ "From negative to positive" → ✅ "From + to - (positive test charge direction)"
Trap 3: Current units
❌ "coulombs per second" → ✅ "amperes (A)" (though C/s is technically correct)
Trap 4: Current direction
Remember: Conventional current (+ to -) is used in exams, even though electrons actually flow the opposite way!
📋 Syllabus Checklist (4.2)
Explain static charging by friction (electron transfer)
State like charges repel, unlike charges attract
Distinguish between conductors and insulators
SUPPLEMENT Describe electric field patterns
SUPPLEMENT Define current as rate of charge flow (I = Q/t)
SUPPLEMENT Distinguish conventional current vs electron flow
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