⚡ CIE IGCSE Physics – Electrical Quantities

1️⃣ Positive and Negative Charges

There are two types of electric charge:

• Positive (+)
• Negative (–)

All matter is made of atoms containing:

• Protons → Positive charge
• Electrons → Negative charge
• Neutrons → No charge

Normally, objects are electrically neutral (equal positive and negative charges).

2️⃣ Forces Between Charges

Charges	Force
Positive & Positive	Repel
Negative & Negative	Repel
Positive & Negative	Attract

👉 Rule to remember:
Like charges repel, unlike charges attract.

This is exactly similar to magnetic poles.

3️⃣ Production and Detection of Electrostatic Charges

🔹 Charging by Friction (Static Electricity)

When two insulating materials are rubbed together:

• Electrons transfer from one material to the other.
• One becomes negatively charged.
• The other becomes positively charged.

Example Experiment:

Rub:

• A plastic rod with a dry cloth
• A balloon on hair

Observation:

• The rod/balloon attracts small paper pieces.
• The balloon sticks to the wall.

🔹 Detecting Electrostatic Charge

Using a Gold-leaf Electroscope

An electroscope detects charge.

How it works:

1. Bring charged object near the metal cap.
2. The gold leaf rises (repels from stem).
3. This shows the presence of charge.

If touched:

• Charge transfers.
• The leaf stays separated.

4️⃣ Charging by Friction – Electron Transfer Only

Important Concept:

Only electrons move.

Protons do NOT move because:

• They are fixed inside the nucleus.

When rubbing:

• Electrons move from one object to another.
• The object that gains electrons becomes negative.
• The object that loses electrons becomes positive.

⚠️ Very common exam question:
“Explain charging by friction.”

Correct answer must mention:
✔ Transfer of electrons
✔ One object gains electrons
✔ One object loses electrons

5️⃣ Conductors and Insulators – Experiment

Simple Experiment:

1. Set up a simple circuit with:
   • Battery
   • Bulb
   • Wires
   • Gap for test material
2. Place material in gap.

If bulb lights → conductor
If bulb does not light → insulator

6️⃣ Electron Model of Conductors and Insulators

🔹 Conductors

Definition:
Materials that allow electric charge to flow easily.

Electron Model:

• Have free (delocalised) electrons
• Electrons move through material

Examples:

• Copper
• Aluminium
• Iron
• Silver
• Graphite

🔹 Insulators

Definition:
Materials that do NOT allow electric charge to flow easily.

Electron Model:

• Electrons are tightly bound to atoms
• No free electrons

Examples:

• Plastic
• Rubber
• Glass
• Wood
• Air

🔥 Key Comparison

Property	Conductor	Insulator
Free electrons?	Yes	No
Current flows?	Yes	No
Example	Copper	Plastic

7️⃣ Charge and the Coulomb

The SI unit of charge is the:

Coulomb (C)

Symbol: Q

Important fact:
1 electron charge = 1.6 × 10⁻¹⁹ C

Formula (sometimes tested):

Where:

• Q = charge (C)
• I = current (A)
• t = time (s)

8️⃣ Electric Field

🔹 Definition

An electric field is:

A region in which an electric charge experiences a force.

If a charged particle is placed in an electric field:

• It experiences a force.

9️⃣ Direction of Electric Field

The direction of an electric field at a point is:

The direction of the force on a positive charge at that point.

Important:

• Electric field direction is always defined using a positive test charge.
• Field lines go from positive to negative.

🔟 Electric Field Patterns

(a) Field Around a Point Charge

Positive Charge:

• Field lines radiate outward.

Negative Charge:

• Field lines radiate inward.

Properties:
✔ Lines are radial
✔ Lines never cross
✔ Arrows show direction
✔ Closer lines = stronger field

(b) Field Around a Charged Conducting Sphere

Similar to a point charge:

• Positive sphere → field lines go outward
• Negative sphere → field lines go inward
• Field lines are perpendicular to surface

Important:
Inside a conductor:

Electric field is zero.

(c) Between Two Oppositely Charged Parallel Plates

This produces a:

Uniform electric field

Characteristics:
✔ Straight lines
✔ Parallel lines
✔ Equally spaced
✔ Direction: positive plate → negative plate

This is called a uniform field because:

• Field strength is constant everywhere between plates.

End effects (curving at edges) are NOT examined.

⚡ Field Strength and Spacing

• Closer lines → Stronger electric field
• Wider spacing → Weaker electric field

🔥 Important Definitions (Memorise These)

Electric charge:
A property of matter that causes it to experience a force in an electric field.

Coulomb:
The SI unit of electric charge.

Electric field:
A region in which an electric charge experiences a force.

Conductor:
A material that allows electric charge to flow through it.

Insulator:
A material that does not allow electric charge to flow through it.

🧠 Common Exam Mistakes

❌ Saying protons move during charging
❌ Forgetting field direction arrows
❌ Drawing curved lines between parallel plates
❌ Not mentioning electron transfer in friction explanation
❌ Saying electric field direction is direction of negative charge

✏️ Drawing Tips for Field Lines

✔ Use smooth lines
✔ Include arrows
✔ Do not let lines cross
✔ Show symmetry
✔ Make spacing realistic

Examiners are strict about:

• Arrow direction
• Neatness
• Correct pattern

🔎 Frequently Asked Exam Questions

1. Explain charging by friction.
2. Describe how to detect electrostatic charge.
3. State the difference between conductors and insulators using electron model.
4. Draw electric field around:
   • Positive charge
   • Negative charge
   • Parallel plates
5. Define electric field.

⚡ Real-Life Applications

• Lightning → Large electrostatic discharge
• Photocopiers → Use electrostatic charges
• Spray painting → Charged paint spreads evenly
• Electrostatic precipitators → Remove smoke particles

📝 Quick Revision Checklist

Make sure you can:

☐ State two types of charge
☐ Describe attraction and repulsion
☐ Explain charging by friction (electrons move only)
☐ Describe conductor vs insulator (electron model)
☐ State unit of charge
☐ Define electric field
☐ State field direction rule
☐ Draw correct field patterns
☐ Explain field strength using spacing

⚡ CIE IGCSE Physics – Electric Current

Comprehensive Notes (Based on Official Syllabus Points)

1️⃣ Electric Current and Flow of Charge

🔹 What is Electric Current?

Electric current is related to the flow of electric charge.

In simple terms:

Electric current is the movement of charged particles.

In metals, the moving charges are electrons.

🔹 What Actually Moves?

• In metal wires → free electrons move
• In electrolyte solutions → positive and negative ions move (not required in detail at this level)

2️⃣ Definition of Electric Current

🔹 Formal Definition (Memorise!)

Electric current is the charge passing a point per unit time.

🔹 Formula

Where:

• ( I ) = current (amperes, A)
• ( Q ) = charge (coulombs, C)
• ( t ) = time (seconds, s)

🔹 Unit of Current

The unit of current is the:

Ampere (A)

1 ampere means:

1 coulomb of charge passes a point in 1 second.

🔹 Example Calculation

If 6 C of charge passes through a wire in 3 seconds:

🔥 Exam Tip

Always:
✔ Write formula
✔ Substitute values
✔ Include unit

3️⃣ Electrical Conduction in Metals

🔹 Electron Model of Metals

Metals contain:

• Positive ions fixed in place
• Free (delocalised) electrons

These free electrons:

• Move randomly when no battery is connected.
• Move in one direction when connected to a power supply.

🔹 When a Battery is Connected

• The battery creates an electric field.
• Free electrons drift towards the positive terminal.
• This movement produces current.

🔹 Important Point

The electrons move slowly (drift velocity),
but the effect of current is almost instant.

4️⃣ Conventional Current vs Electron Flow

This is VERY important for exams.

🔹 Conventional Current

Defined as:

The flow of positive charge from positive to negative.

Direction:
Positive → Negative

🔹 Electron Flow

Electrons actually move:

Negative → Positive

🔹 Why the Difference?

Historically:

• Scientists assumed current was positive before electrons were discovered.
• The definition was never changed.

🔥 Exam Warning

If asked:
“State the direction of conventional current”

Correct answer:
✔ From positive to negative.

5️⃣ Direct Current (d.c.) vs Alternating Current (a.c.)

🔹 Direct Current (d.c.)

Definition:

Current that flows in one direction only.

Produced by:

• Batteries
• Cells
• Power banks

Graph:

• Straight horizontal line above zero.

Example:
Torch, phone battery.

🔹 Alternating Current (a.c.)

Definition:

Current that changes direction repeatedly.

Produced by:

• Mains electricity supply

In most countries:

• 50 Hz (changes direction 50 times per second)

Graph:

• Sine wave.

🔥 Comparison Table

Feature	d.c.	a.c.
Direction	One direction	Changes direction
Source	Battery	Mains
Graph	Straight line	Wave

6️⃣ Measuring Current – Ammeters

🔹 What is an Ammeter?

An ammeter measures electric current.

🔹 How to Connect an Ammeter

It must be connected:

In series with the component.

Reason:

• Current is the same at all points in a series circuit.

🔹 Analogue Ammeter

• Has a needle.
• Must read carefully.
• Watch for:
  • Parallax error
  • Correct scale
  • Zero error

🔹 Digital Ammeter

• Displays reading directly.
• No parallax error.
• Easier to read.

🔹 Different Ranges

Ammeters have different ranges (e.g., 0–1 A, 0–5 A).

Why?

• To measure small and large currents accurately.
• Choose the smallest suitable range for better precision.

🔥 Exam Tip

If current is small:

• Use smaller range for more accurate reading.

If current is too large:

• Ammeter may be damaged.

⚡ Important Concepts Students Must Understand

🔹 Current in Series Circuits

Current is the same everywhere in a series circuit.

🔹 Current in Parallel Circuits

Current splits between branches.

Total current = sum of branch currents.

🧠 Common Exam Questions

1. Define electric current.
2. State the unit of current.
3. Calculate current using I = Q/t.
4. State difference between d.c. and a.c.
5. State direction of conventional current.
6. Explain conduction in metals using free electrons.
7. Describe how to connect an ammeter.

🚨 Common Mistakes

❌ Saying current is flow of energy
❌ Saying protons move in wires
❌ Mixing up electron flow and conventional current
❌ Connecting ammeter in parallel
❌ Forgetting units

📝 Important Definitions (Memorise Exactly)

Electric current:
The charge passing a point per unit time.

Ampere:
One coulomb of charge passing a point per second.

Direct current (d.c.):
Current flowing in one direction only.

Alternating current (a.c.):
Current that changes direction repeatedly.

Conventional current:
Flow of positive charge from positive to negative.

⚡ Real-Life Examples

• Phone charging → d.c.
• House electricity → a.c.
• Car battery → d.c.
• Power stations → produce a.c.

🔎 Quick Revision Checklist

Make sure you can:

☐ Define current
☐ Use I = Q/t
☐ State unit of current
☐ Explain conduction in metals
☐ State conventional current direction
☐ Explain difference between d.c. and a.c.

☐ Describe correct ammeter connection
☐ Choose correct ammeter range

⚡

⚡ CIE IGCSE Physics – Electromotive Force (e.m.f.) and Potential Difference (p.d.)

1️⃣ Electromotive Force (e.m.f.)

🔹 Definition (Memorise Exactly)

Electromotive force (e.m.f.) is the electrical work done by a source in moving a unit charge around a complete circuit.

Key ideas:

• It is the energy supplied by the source.
• It refers to the entire circuit.
• The source is usually a battery or power supply.

🔹 Formula for e.m.f.

Where:

• (E) = e.m.f. (volts, V)
• (W) = work done / energy supplied (joules, J)
• (Q) = charge (coulombs, C)

🔹 Unit of e.m.f.

The unit is the:

Volt (V)

1 volt means:

1 joule of energy supplied per coulomb of charge.

🔹 Example Calculation (e.m.f.)

If a battery supplies 12 J of energy to move 3 C of charge:

🔥 Important Concept

e.m.f. is:

• The maximum energy per unit charge supplied by the battery.
• Measured when no current flows (open circuit).

2️⃣ Potential Difference (p.d.)

🔹 Definition (Memorise Exactly)

Potential difference is the work done by a unit charge passing through a component.

Key idea:

• It is the energy transferred to components.
• It refers to two points in a circuit.

🔹 Formula for Potential Difference

Where:

• (V) = potential difference (volts, V)
• (W) = energy transferred (joules, J)
• (Q) = charge (coulombs, C)

🔹 Unit of p.d.

Also measured in:

Volts (V)

1 volt = 1 joule per coulomb.

🔹 Example Calculation (p.d.)

If 10 J of energy is transferred when 2 C passes through a resistor:

3️⃣ Difference Between e.m.f. and p.d.

This is VERY commonly tested.

e.m.f.	Potential Difference
Energy supplied by source	Energy transferred to component
Around whole circuit	Across component
Measured across battery	Measured across component
Maximum energy per charge	Energy used per charge

🔥 Simple Way to Think About It

Battery = energy supplier
Components = energy users

So:

• e.m.f. = energy supplied
• p.d. = energy used

4️⃣ Measuring Potential Difference – Voltmeters

🔹 What is a Voltmeter?

A voltmeter measures potential difference.

🔹 How to Connect a Voltmeter

It must be connected:

In parallel with the component.

Reason:

• Measures difference between two points.
• Does not interrupt current.

⚠️ Common Exam Trap

Ammeter → Series
Voltmeter → Parallel

5️⃣ Analogue vs Digital Voltmeters

🔹 Analogue Voltmeter

• Has a needle and scale.
• Must avoid parallax error.
• Must check zero error.
• Choose the correct range.

🔹 Digital Voltmeter

• Displays reading directly.
• No parallax error.
• Easier to use.

6️⃣ Using Different Ranges

Voltmeters have different ranges (e.g., 0–3 V, 0–15 V).

Why?

• For better precision.
• To avoid damage.
• Use the smallest suitable range.

🔥 Exam Tip

If expected voltage is about 2 V:

• Use 3 V range, not 15 V range.

Smaller range → More accurate reading.

7️⃣ Energy Transfer in Circuits

When current flows:

Battery supplies energy → components convert it into:

• Light (bulb)
• Heat (resistor)
• Sound (speaker)
• Motion (motor)

Total energy supplied by battery = total energy used by components (in ideal case).

8️⃣ Relationship Between Energy and Charge

From formula:

So:
Energy transferred = Voltage × Charge

This is very useful in calculations.

🧠 Common Exam Questions

1. Define electromotive force.
2. Define potential difference.
3. State the unit of e.m.f.
4. State the unit of p.d.
5. Calculate voltage using (V = W/Q).
6. Explain the difference between e.m.f. and p.d.
7. Describe how to connect a voltmeter.

🚨 Common Mistakes

❌ Saying e.m.f. is a force (it is NOT a force)
❌ Confusing e.m.f. with current
❌ Connecting voltmeter in series
❌ Forgetting unit (V)
❌ Not writing full definitions

📝 Important Definitions (Memorise)

Electromotive force (e.m.f.):
The electrical work done by a source in moving a unit charge around a complete circuit.

Potential difference (p.d.):
The work done by a unit charge passing through a component.

Volt:
One joule of energy per coulomb of charge.

⚡ Worked Example Combining Concepts

A 12 V battery moves 5 C of charge around a circuit.

Energy supplied:

So the battery supplies 60 J of energy.

🔎 Quick Revision Checklist

Make sure you can:

☐ Define e.m.f.
☐ Define potential difference
☐ State unit (volt)
☐ Use (E = W/Q)
☐ Use (V = W/Q)
☐ Rearrange to find (W = VQ)
☐ Explain difference between e.m.f. and p.d.
☐ Describe correct voltmeter connection
☐ Choose correct voltmeter range

🔥 Final Exam Advice

Examiners love:

• Exact wording of definitions.
• Clear distinction between e.m.f. and p.d.
• Correct circuit connections.
• Correct units in calculations.

⚡ CIE IGCSE Physics – Resistance

Comprehensive Notes (Based on Official Syllabus Points)

1️⃣ Definition of Resistance

🔹 What is Resistance?

Resistance is:

The opposition to the flow of electric current.

It tells us how difficult it is for current to flow through a component.

Symbol: R
Unit: Ohm (Ω)

🔹 Formula for Resistance (Ohm’s Law)

R = V ÷ I

Where:

• (R) = resistance (ohms, Ω)
• (V) = potential difference (volts, V)
• (I) = current (amperes, A)

🔹 Rearranged Forms (Very Important)

🔹 Example Calculation

If:

• Voltage = 12 V
• Current = 3 A

🔥 Exam Tip

Always:
✔ Write formula
✔ Substitute values
✔ Include unit (Ω)

2️⃣ Experiment to Determine Resistance

🔹 Apparatus

• Power supply
• Resistor
• Ammeter (in series)
• Voltmeter (in parallel)
• Variable resistor (optional)

🔹 Circuit Setup

• Ammeter → series
• Voltmeter → parallel across resistor

🔹 Procedure

1. Set up the circuit correctly.

2. Record current (I) from ammeter.

3. Record voltage (V) from voltmeter.

4. Calculate resistance using:

   

5. Repeat for different voltages.

6. Take the average value.

🔹 Example Data Table

Voltage (V)	Current (A)	Resistance (Ω)
2	0.5	4
4	1.0	4
6	1.5	4

Resistance remains constant → Ohmic conductor.

🔥 Common Exam Points

Must mention:
✔ Ammeter in series
✔ Voltmeter in parallel
✔ Use of R = V/I
✔ Multiple readings for accuracy

3️⃣ Resistance of a Metallic Wire

🔹 Effect of Length

Resistance is:

Directly proportional to length.

Longer wire → Higher resistance.

Reason:

• Electrons collide more.
• More opposition to flow.

🔹 Effect of Cross-sectional Area

Resistance is:

Inversely proportional to cross-sectional area.

Thicker wire → Lower resistance.

Reason:

• More space for electrons to move.
• Less opposition.

🔹 Relationship Summary

Where:

• (L) = length
• (A) = cross-sectional area

4️⃣ Current–Voltage (I–V) Graphs

A very important exam topic.

🔹 (A) Resistor of Constant Resistance (Ohmic Conductor)

Examples:

• Metal resistor (at constant temperature)

Graph Shape:

• Straight line through origin.

Explanation:

• Current is directly proportional to voltage.
• Resistance is constant.
• Obeys Ohm’s Law.

🔹 (B) Filament Lamp

Graph Shape:

• Curved.
• Gets less steep as voltage increases.

Explanation:

• As current increases → temperature increases.
• Higher temperature → higher resistance.
• So current increases more slowly.

🔹 (C) Diode

Graph Shape:

• No current in reverse direction.
• Very small current until threshold voltage.
• After threshold → current increases rapidly.

Explanation:

• Diode allows current in one direction only.

🔥 Comparison Table

Component	Graph Shape	Resistance Behaviour
Resistor	Straight line	Constant
Filament lamp	Curved	Increases with temperature
Diode	One-direction curve	Very high in reverse

5️⃣ Mathematical Relationships for Metallic Conductor

For a metal wire:

(a) Resistance ∝ Length

If length doubles → resistance doubles.

(b) Resistance ∝ 1 / Cross-sectional Area

If area doubles → resistance halves.

🔹 Combined Relationship (Extension)

Where:

• ρ = resistivity (not always required at IGCSE)

🧠 Common Exam Questions

1. State formula for resistance.
2. Describe an experiment to determine resistance.
3. Sketch I–V graph for:
   • Resistor
   • Filament lamp
   • Diode
4. Explain why filament lamp graph curves.
5. State relationship between resistance and length.
6. State relationship between resistance and area.

🚨 Common Mistakes

❌ Drawing straight line for filament lamp
❌ Forgetting diode blocks reverse current
❌ Connecting voltmeter in series
❌ Forgetting units (Ω)
❌ Saying resistance decreases with length

📝 Important Definitions (Memorise)

Resistance:
Opposition to the flow of electric current.

Ohm:
The resistance when a current of 1 A flows due to a p.d. of 1 V.

Ohmic conductor:
A conductor that obeys Ohm’s Law (straight line I–V graph).

⚡ Real-Life Examples

• Heating elements → high resistance
• Fuse wire → thin (high resistance)
• Power cables → thick (low resistance)
• Light bulb filament → resistance increases when hot

🔎 Quick Revision Checklist

Make sure you can:

☐ Use R = V/I
☐ Rearrange Ohm’s Law
☐ Describe resistance experiment
☐ Sketch correct I–V graphs
☐ Explain filament lamp curve
☐ Explain diode graph
☐ State R ∝ L
☐ State R ∝ 1/A
☐ Include correct units

🔥 Final Exam Advice

Examiners love:

✔ Clear circuit diagrams
✔ Correct graph shapes
✔ Proper explanation of temperature effect
✔ Correct proportionality statements
✔ Correct units

⚡ CIE IGCSE Physics – Electrical Energy and Electrical Power

Comprehensive Notes (Based on Official Syllabus Points)

1️⃣ Energy Transfer in Electric Circuits

🔹 Key Idea

Electric circuits transfer energy, not charge.

The battery or mains supply provides energy.
The components convert that energy into other forms.

🔹 Energy Flow in a Circuit

Source (battery or mains) → Wires → Components → Surroundings

Examples of energy conversions:

Component	Energy Conversion
Lamp	Electrical → Light + Heat
Heater	Electrical → Heat
Motor	Electrical → Kinetic (movement)
Speaker	Electrical → Sound

🔥 Important Concept

• Charges carry energy around the circuit.
• Energy is transferred to components.
• Charge is not used up.
• Energy is transferred.

This is a very common exam misconception.

2️⃣ Electrical Power

🔹 Definition

Electrical power is the rate at which electrical energy is transferred.

In simple terms:
Power tells us how fast energy is being used.

🔹 Formula for Electrical Power

Where:

• (P) = power (watts, W)
• (I) = current (amperes, A)
• (V) = voltage (volts, V)

🔹 Unit of Power

The unit is:

Watt (W)

1 watt = 1 joule per second.

🔹 Example Calculation

A device uses:

• 2 A
• 12 V

🔥 What Power Means Physically

If a device has power of 24 W:

It transfers 24 joules of energy every second.

3️⃣ Electrical Energy

🔹 Formula for Electrical Energy

Where:

🔹 Alternative Form

Since:

Then:

Both forms are very important.

🔹 Example Calculation

A 60 W bulb is used for 10 seconds.

The bulb transfers 600 joules of energy.

4️⃣ Kilowatt-hour (kWh)

🔹 Why We Use kWh

Joules are too small for household energy.

So electricity companies use:

Kilowatt-hour (kWh)

🔹 Definition (Memorise!)

One kilowatt-hour is the energy transferred when a 1 kW appliance operates for 1 hour.

🔹 Conversion

1 kW = 1000 W
1 hour = 3600 s

5️⃣ Calculating Energy in kWh

🔹 Example

A 2 kW heater runs for 3 hours.

6️⃣ Calculating Cost of Electricity

Electricity bills use:

🔹 Example

If electricity costs $0.20 per kWh:

Energy used = 6 kWh

Cost = $1.20

🔥 Full Example Question

A 500 W microwave is used for 30 minutes.
Electricity costs $0.25 per kWh.

Step 1: Convert power to kW

500 W = 0.5 kW

Step 2: Convert time to hours

30 minutes = 0.5 hours

Step 3: Calculate energy

Step 4: Calculate cost

Cost = $0.063 (approx)

---

7️⃣ Important Relationships Summary

8️⃣ Common Exam Mistakes

❌ Forgetting to convert W to kW
❌ Forgetting to convert minutes to hours
❌ Mixing up joules and kWh
❌ Saying charge is used up
❌ Forgetting units

9️⃣ Important Definitions (Memorise)

Electrical power:
The rate at which electrical energy is transferred.

Electrical energy:
Energy transferred by an electric current.

Kilowatt-hour:
The energy transferred when a 1 kW appliance operates for 1 hour.

🔟 Real-Life Applications

• Electric kettle → high power (boils quickly)
• LED bulb → low power (energy efficient)
• Electric heater → high energy use
• Phone charger → low power

🧠 Exam Tip: Comparing Appliances

Higher power:

• Transfers energy faster
• Costs more per hour

Longer time:

• Uses more energy
• Increases cost

🔎 Quick Revision Checklist

Make sure you can:

☐ Explain energy transfer in circuit
☐ Use P = IV
☐ Use E = IVt
☐ Use E = Pt
☐ Convert W to kW
☐ Convert minutes to hours
☐ Define kWh
☐ Calculate cost of electricity
☐ Include correct units