Year 10 physicsAQA GCSE Physics & Combined Science

Follow the charge.
Track the energy.

Circuits, current, p.d., resistance, power, mains
Static electricity Triple only

\(Q = I\,t\)\(E = Q\,V\)\(V = I\,R\)\(P = V\,I\)\(P = I^2\,R\)\(E = P\,t\)

ELECTRONS
− → +

ENERGY
OUT AT
EACH PART

ONE LOOP, ONE CURRENT

Same current
all the way round.

\(V = I\,R\)

AQA Physics 8463: 4.2 · Combined Science 8464: 6.2

Nine missions.

01A

Build & measure

Loops, symbols, ammeter

Physics 4.2.1.1Combined 6.2.1.1

02Q

Charge on the move

Current, \(Q = I\,t\)

Physics 4.2.1.2Combined 6.2.1.2

03V

Energy per coulomb

p.d., \(E = Q\,V\), voltmeter

Physics 4.2.4.2Combined 6.2.4.2

04Ω

Resistance &
\(V = I\,R\)

Ohm’s law, RP: wire length

Physics 4.2.1.3Combined 6.2.1.3

05

Series & parallel

The rules, \(R_{\text{total}}\)

Physics 4.2.2Combined 6.2.2

06I–V

\(I\)–\(V\) characteristics

Lamp, diode, sensors, RP

Physics 4.2.1.4Combined 6.2.1.4

07P

Power & the Grid

\(P = V\,I\), \(E = P\,t\), transformers

Physics 4.2.4Combined 6.2.4

08~

Mains & safety

ac, 230 V, earth wire

Physics 4.2.3Combined 6.2.3

09±

Static Triple only

Rubbing, sparks, electric fields

Physics 4.2.5Not in Combined

Electric circuits

01 Mission 1: Wire it like a physicist

Build & measure

complete circuitscircuit symbolsammeter in series

AQA spec: Physics 4.2.1.1Combined Science 6.2.1.1

KEY RULE

No complete loop, no current

Mission 1: Build & measure

01 What a circuit needs

A complete loop

A source of energy: cell or battery
A closed loop of conducting wire
Wires are already full of charge
Close the switch → all the charge moves at once
A gap anywhere → no current everywhere

Mission 1: Build & measure

01 Learn to draw all of these

Circuit symbols

Cell: the longer line is the positive terminal

Battery: two or more cells joined together

Mission 1: Build & measure

01 Anyone can build it

Draw it properly

Pencil and ruler
Straight wires, right-angle corners
No gaps: every wire joins at both ends
Wire goes into each symbol
Label values: 6 V, 10 Ω

Mission 1: Build & measure

01 Measuring current

Ammeter in series

Current in amperes (A)
Ammeter in the same loop as the component
Same charge flows through both
Ideal ammeter: almost zero resistance

One loop \(=\) a series circuit

Mission 1: Build & measure

02 Mission 2: Measure the flow

Charge on the move

current as a rate\(Q = I\,t\)electrons vs conventional current

AQA spec: Physics 4.2.1.2Combined Science 6.2.1.2

KEY RULE

Current = charge per second

Mission 2: Charge on the move

02 Current

A rate of flow

Current = rate of flow of charge
Charge \(Q\) in coulombs (C)
Current I in amperes (A)
1 A \(=\) 1 C passing a point each second
In metals: free electrons move
Needs a closed loop + a p.d.

Mission 2: Charge on the move

02 Know and apply

Charge flow

\(Q = I\,t\)\(\text{charge flow} = \text{current} \times \text{time}\)\(Q\) in C, \(I\) in A, \(t\) in s

Time in seconds: min \(\times 60\), h \(\times 3600\)

Example 10.40 A for 3.0 minutes

Convert: \(t = 3.0 \times 60 = 180\) s
Substitute: \(Q = 0.40 \times 180\)
Answer: \(Q = 72\) C

Example 25400 C at 1.2 A. Time in minutes?

Rearrange: \(t = Q \div I = 5400 \div 1.2\)
Answer: \(4500\ \text{s} = 75\ \text{min}\)

Mission 2: Charge on the move

02 Which way?

Two directions

Electrons: − terminal → + terminal
Conventional current: + → −
Circuit arrows use conventional current
Same current, opposite arrows

Mission 2: Charge on the move

02 Common mistake

Current is not used up

One loop → same current everywhere
Charge is conserved: it goes round
Components take energy, not charge

“The lamp uses up some current.”

The lamp transfers energy. Current stays the same.

Mission 2: Charge on the move

01–02 Checkpoint

Quick check

145 C flows in 30 s. Current?

\(I = 45 \div 30 = 1.5\) A

20.25 A for 2.0 min. Charge?

\(0.25 \times 120 = 30\) C

3Ammeter: series or parallel?

Series, in the same loop

4Which way do electrons flow?

− terminal → + terminal

5Ammeters before and after a lamp?

Same reading

6Switch opened. Current?

Zero everywhere: the loop is broken

PRESS → TO REVEAL EACH ANSWER

03 Mission 3: Follow the energy

Energy per coulomb

p.d. \(=\) energy per coulomb\(E = Q\,V\)voltmeter across

AQA spec: Physics 4.2.4.2Combined Science 6.2.4.2

KEY RULE

1 V \(=\) 1 J per coulomb

Mission 3: Energy per coulomb

03 Know and apply

Potential difference

p.d. = energy transferred per coulomb
Measured in volts (V)
6 V across a resistor → 6 J per C

\(E = Q\,V\)\(\text{energy} = \text{charge flow} \times \text{p.d.}\)\(E\) in J, \(Q\) in C, \(V\) in V

Two steps12 V motor, 0.50 A for 40 s. Energy?

Charge: \(Q = I\,t = 0.50 \times 40 = 20\) C
Equation: \(E = Q\,V\)
Substitute: \(E = 20 \times 12\)
Answer: \(E = 240\) J

Mission 3: Energy per coulomb

03 Measuring p.d.

Voltmeter across

p.d. is between two points
Voltmeter in parallel, across the part
Very high resistance
Both leads on one wire → about 0 V

“The voltage at the resistor.”

“The p.d. across the resistor.”

Mission 3: Energy per coulomb

03 Source and load

Energy in. Energy out.

Source (battery): energy to the charge
Load (lamp, resistor): energy from the charge
Series: component p.d.s add up to the supply
6 J supplied \(=\) 3 J \(+\) 3 J transferred

Charge is conserved and energy is conserved

Mission 3: Energy per coulomb

04 Mission 4: Control the current

Resistance & \(V = I\,R\)

\(V = I\,R\)Ohm’s lawwhy metals resistRP: length of a wire

AQA spec: Physics 4.2.1.3Combined Science 6.2.1.3

KEY RULE

More resistance, less current

Mission 4: Resistance

04 Know and apply

Resistance equation

\(V = I\,R\)\(\text{p.d.} = \text{current} \times \text{resistance}\)\(V\) in V, \(I\) in A, \(R\) in Ω

\(R = V \div I\) and \(I = V \div R\)
Same p.d., double \(R\) → half the current
mA \(\div 1000\) → A

Example 10.20 A through 15 Ω. p.d.?

Substitute: \(V = 0.20 \times 15\)
Answer: \(V = 3.0\) V

Example 26.0 V, 250 mA. Resistance?

Convert: \(250\ \text{mA} = 0.25\ \text{A}\)
Answer: \(R = 6.0 \div 0.25 = 24\) Ω

Mission 4: Resistance

04 Ohm’s law

Ohmic conductors

\(I\) directly proportional to \(V\)
Only at constant temperature
Straight line through the origin
Resistance stays constant

Double the p.d. → double the current

Mission 4: Resistance

04 Inside the metal

Why metals resist

Electrons collide with metal ions
Collisions oppose the current
Energy transferred → wire heats up
Hotter → ions vibrate more → more collisions
So \(R\) increases with temperature

Mission 4: Resistance

04 The standard circuit

Measure \(R\)

Ammeter in series
Voltmeter across the component
Variable resistor → change I
Record \(V\) and \(I\) for several pairs
\(R = V \div I\), then a mean or a graph

Mission 4: Resistance

RP Resistance: Part A

Length of a wire

IV: length / cm
DV: resistance / Ω
Control: material, diameter, temperature

10 → 100 cm, in steps
Read \(V\) and \(I\)
\(R = V \div I\)
Switch off between readings

Required practical: Resistance

RP Results and evaluation

\(R \propto\) length

Straight line through origin → \(R \propto L\)
Longer wire → more collisions
Wire heats → \(R\) rises → keep current small
Measure to the same contact point of the clip

“Human error.”

“The wire heated up, so \(R\) increased.”

Required practical: Resistance

03–04 Checkpoint

Quick check

15.0 C through a 12 V lamp. Energy?

\(E = 5.0 \times 12 = 60\) J

269 000 J, 300 C. p.d.?

\(V = 69\,000 \div 300 = 230\) V

3How is a voltmeter connected?

In parallel, across the component

46.0 V, 0.30 A. Resistance?

\(R = 6.0 \div 0.30 = 20\) Ω

5Wire length doubles. Resistance?

Doubles: \(R \propto L\)

6Why switch off between readings?

Stops the wire heating, so \(R\) stays constant

PRESS → TO REVEAL EACH ANSWER

05 Mission 5: Crack any network

Series & parallel

series rulesparallel rules\(R_{\text{total}} = R_1 + R_2\)

AQA spec: Physics 4.2.2Combined Science 6.2.2

KEY RULE

Parallel: same p.d., currents add

Mission 5: Series & parallel

05 One path

Series rules

Same current through every part
Supply p.d. shared between parts
Bigger \(R\) → bigger share of p.d.

\(R_{\text{total}} = R_1 + R_2\)total resistance in series

Mission 5: Series & parallel

05 More than one path

Parallel rules

Same p.d. across each branch
Branch currents add up to the total
Smaller \(R\) → bigger branch current
\(R_{\text{total}}\) less than the smallest resistor

Each branch gets the full supply p.d.

Mission 5: Series & parallel

RP Resistance: Part B

Another path, less \(R\)

Series: add a resistor → \(R_{\text{total}}\) up
Parallel: add a branch → more paths
More current at the same p.d.
So \(R_{\text{total}} = V \div I\) goes down

Two 10 Ω resistors
Series	20 Ω
Parallel	5 Ω

Mission 5: Series & parallel

05 Worked example

Find the lamp’s \(R\)

9.0 V supply, 10 Ω reads 6.0 VResistance of the lamp?

Current: \(I = 6.0 \div 10 = 0.60\) A
Lamp p.d.: \(9.0 - 6.0 = 3.0\) V
Same I: 0.60 A in series
Answer: \(R = 3.0 \div 0.60 = 5.0\) Ω

Mission 5: Series & parallel

05 Checkpoint

Quick check

15 Ω and 15 Ω in series. \(R_{\text{total}}\)?

\(5 + 15 = 20\) Ω

2Series: 12 V supply, one part has 5 V?

The other has 7 V

3Branches: 0.4 A and 0.6 A. Supply current?

\(0.4 + 0.6 = 1.0\) A

4p.d. across each parallel branch?

The full supply p.d.

5Add a resistor in parallel. \(R_{\text{total}}\)?

Decreases

66.0 V, 0.20 A, \(R_1 = 12\) Ω. \(R_2\) in series?

\(30 - 12 = 18\) Ω

PRESS → TO REVEAL EACH ANSWER

06 Mission 6: A component’s fingerprint

\(I\)–\(V\) characteristics

resistor, lamp, diodethermistors and LDRsRP: \(I\)–\(V\)

AQA spec: Physics 4.2.1.4Combined Science 6.2.1.4

KEY RULE

Curved graph, changing \(R\)

Mission 6: \(I\)–\(V\) characteristics

06 Reading the graph

Current against p.d.

p.d. on \(x\), current on \(y\)
Negative values: supply reversed
Straight through origin → ohmic
Curve → \(R\) changes

Fixed resistor: same shape both ways

Mission 6: \(I\)–\(V\) characteristics

06 Non-ohmic

Lamp & diode

Filament lamp

More current → filament hotter
Hotter → \(R\) increases
Graph gets less steep

Diode (and LED)

Current in one direction only
Very high \(R\) in reverse
Forward: a diode conducts above ~0.6 V (an LED needs more)

Mission 6: \(I\)–\(V\) characteristics

The lamp’s curve comes from electrons colliding with ions (Mission 4)

At low current the filament is cool, its resistance is low and the line is steep. As it heats up, each extra volt gives less extra current, so the line bends over.

A diode is a one-way valve for charge

It is used to turn ac into dc, and to protect circuits from a battery connected the wrong way round.

A cold filament has a much lower resistance than a hot one, so the current is largest at switch-on. That is when old filament lamps usually failed.

The 0.6 V is a typical value for a silicon diode; you do not need to learn it. The AQA specification says: “The current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction.” (Physics 4.2.1.4, Combined Science 6.2.1.4)

06 Components that sense

Thermistor & LDR

Thermistor

Temperature ↑ → \(R\) ↓
Thermostats, fire alarms

Light-dependent resistor

Light intensity ↑ → \(R\) ↓
Streetlights, night lights

Mission 6: \(I\)–\(V\) characteristics

06 On the bench

What they look like

Clear glass filament lamp with a visible coiled wire inside — **Filament lamp**Hotter → **\(R\) ↑**

Black cylindrical diode with a silver polarity band and two wire leads — **Diode**Current **one way** only

Red light-emitting diode with a rounded plastic case and two wire leads — **LED**A diode that **emits light**

Small black bead thermistor with two wire leads — **Thermistor**Temperature ↑ → **\(R\) ↓**

Light-dependent resistor with an upward-facing serpentine sensing surface and two leads beneath the disc — **LDR**Light intensity ↑ → **\(R\) ↓**

Sliding variable resistor with a wire-wound tube and an adjustable contact — **Variable resistor**Sets **\(R\)** by hand

Mission 6: \(I\)–\(V\) characteristics

06 Sensor circuit

Brighter → more current

Light gets brighter
LDR resistance decreases
Total resistance decreases
\(I = V \div R\) → current increases

6.0 V supplyBright: \(6.0 \div 600 = 0.010\) A
Dark: \(6.0 \div 1500 = 0.0040\) A

Mission 6: \(I\)–\(V\) characteristics

RP \(I\)–\(V\) characteristics

Test each component

Build the circuit
Change the p.d. with the variable resistor
Record \(V\) and \(I\) for several values
Reverse the supply, then repeat
Plot \(I\) against \(V\)
Repeat: resistor, lamp, diode

Required practical: \(I\)–\(V\)

RP Get the negative half

Reverse & read

Required practical: \(I\)–\(V\)

06 Checkpoint

Quick check

1Straight line through the origin?

An ohmic conductor, e.g. a fixed resistor at constant temperature

2Why does the lamp graph curve?

Filament heats, so \(R\) increases

3Diode in reverse?

Very high \(R\), so almost no current

4Thermistor gets hotter. \(R\)?

Decreases

5Sensor for a streetlight?

LDR

6Why reverse the supply?

To get the negative readings

PRESS → TO REVEAL EACH ANSWER

07 Mission 7: Count the joules

Power & the National Grid

\(P = V\,I\), \(P = I^2\,R\)\(E = P\,t\)step-up, step-down

AQA spec: Physics 4.2.4Combined Science 6.2.4

KEY RULE

Power = energy per second

\(P = V\,I\)

1 W \(=\) 1 J per second
1 kW \(=\) 1000 W

Mission 7: Power & the Grid

07 Know and apply

Two power equations

\(P = V\,I\)\(\text{power} = \text{p.d.} \times \text{current}\)\(P\) in W, \(V\) in V, \(I\) in A

Example230 V, 4.0 A → \(P = 230 \times 4.0 =\) 920 W

\(P = I^2\,R\)\(\text{power} = \text{current}^2 \times \text{resistance}\)\(P\) in W, \(I\) in A, \(R\) in Ω

Example2.0 A, 15 Ω → \(P = 2.0^2 \times 15 =\) 60 W

Square the current first: double \(I\) → \(4 \times\) the power

Mission 7: Power & the Grid

07 Know and apply

Energy transferred

\(E = P\,t\)\(\text{energy} = \text{power} \times \text{time}\)\(E\) in J, \(P\) in W, \(t\) in s

Kettle → thermal store of water
Fan motor → kinetic energy
Charger → chemical store of battery

Example2.0 kW kettle for 3.0 minutes

Convert: \(P = 2000\) W, \(t = 180\) s
Equation: \(E = P\,t\)
Substitute: \(E = 2000 \times 180\)
Answer: \(E = 360\,000\) J

Mission 7: Power & the Grid

07 Power station to home

The National Grid

Cables + transformers
Step-up: p.d. up for transmission
High p.d. → small current
Small current → less heating in cables
Step-down: p.d. down for homes

WhyAn efficient way to transfer energy

Mission 7: Power & the Grid

07 Spot it outside

The Grid, for real

Three tall steel pylons carrying cables into a fenced substation — **Pylons** carry the cables at a **high p.d.**, far above the ground. These stand at a National Grid substation in Monk Fryston. Photo: Gerald England, CC BY-SA 2.0

A grey metal transformer with curved cooling pipes inside a wooden fence — **Transformers** change the p.d.: stepped up for the cables, stepped down for homes. This one is at a local substation. Photo: Bob Harvey, CC BY-SA 2.0

Mission 7: Power & the Grid

07 Power in = power out

Transformer equation

\(V_{\mathrm{p}}\,I_{\mathrm{p}} = V_{\mathrm{s}}\,I_{\mathrm{s}}\)power in = power out\(\mathrm{p}\) = primary (input), \(\mathrm{s}\) = secondary (output)Assumes 100% efficient

Example25 kV, 1200 A in, 400 kV out. \(I_{\mathrm{s}}\)?

Rearrange: \(I_{\mathrm{s}} = V_{\mathrm{p}}\,I_{\mathrm{p}} \div V_{\mathrm{s}}\)
Substitute: \(25\,000 \times 1200 \div 400\,000\)
Answer: \(I_{\mathrm{s}} = 75\) A

p.d. stepped up \(\times 16\) → current stepped down \(\times 16\)

Mission 7: Power & the Grid

07 Checkpoint

Quick check

112 V headlamp, 5.0 A. Power?

\(P = 12 \times 5.0 = 60\) W

23.0 A through 20 Ω. Power?

\(P = 3.0^2 \times 20 = 180\) W

39.0 kW shower for 8.0 min. Energy?

\(9000 \times 480 = 4\,320\,000\) J

4Current doubles, same R. Power?

4 times bigger

5Why transmit at high p.d.?

Small current, less heating, more efficient

6Job of a step-down transformer?

Lowers the p.d. to a safer value for homes

PRESS → TO REVEAL EACH ANSWER

08 Mission 8: Stay safe at 230 V

Mains & safety

ac vs dc230 V, 50 Hzlive, neutral, earth

AQA spec: Physics 4.2.3Combined Science 6.2.3

KEY RULE

Switched off ≠ safe

Mission 8: Mains & safety

08 Two kinds of supply

dc vs ac

dc: one direction only (cells, batteries)
ac: keeps reversing direction
UK mains is ac

p.d.about 230 V

Frequency50 Hz

50 Hz = 50 complete cycles every second

Mission 8: Mains & safety

08 Three-core cable

Three wires, three jobs

Wire	Colour	Job
Live	Brown	Carries the alternating p.d.
Neutral	Blue	Completes the circuit, \(\approx 0\) V
Earth	Green + yellow	Safety wire at 0 V; current only in a fault

Mission 8: Mains & safety

08 Find the three wires

Inside a UK plug

An open UK three-pin plug: a green and yellow wire runs to the top pin, a blue wire to the bottom left pin and a brown wire to a fuse on the right — Photo: Alby Reid, public domain

EarthGreen + yellow, to the top pin
NeutralBlue, to the bottom left pin
LiveBrown, to the fuse, then the bottom right pin

The same three wires run through the cable to the appliance.

Mission 8: Mains & safety

08 Staying safe

Why live is dangerous

Body at 0 V, live at 230 V
Touch live → current through you: shock
Still live with the switch off
Live–earth link → huge current, fire risk
Metal case is earthed: fault current → earth

“The earth wire is at 230 V.”

Earth is at 0 V.

Mission 8: Mains & safety

08 Checkpoint

Quick check

1UK mains supply?

ac, about 230 V, 50 Hz

2What colour is the live wire?

Brown

3p.d. between live and earth?

About 230 V

4Which wire carries current only in a fault?

Earth (green and yellow)

5Switch off. Is the live wire safe?

No, it is still at about 230 V

6Does neutral carry current normally?

Yes, it completes the circuit

PRESS → TO REVEAL EACH ANSWER

Learn to use these

Equation toolkit

\(Q = I\,t\)\(\text{charge} = \text{current} \times \text{time}\)\(Q\) in C, \(I\) in A, \(t\) in sOn the sheet

\(E = Q\,V\)\(\text{energy} = \text{charge} \times \text{p.d.}\)\(E\) in J, \(Q\) in C, \(V\) in VOn the sheet

\(V = I\,R\)\(\text{p.d.} = \text{current} \times \text{resistance}\)\(V\) in V, \(I\) in A, \(R\) in ΩOn the sheet

\(R_{\text{total}} = R_1 + R_2\)series resistanceall in Ω, series onlyLearn it

\(P = V\,I\)\(\text{power} = \text{p.d.} \times \text{current}\)\(P\) in W, \(V\) in V, \(I\) in AOn the sheet

\(P = I^2\,R\)\(\text{power} = \text{current}^2 \times \text{resistance}\)\(P\) in W, \(I\) in A, \(R\) in ΩOn the sheet

\(E = P\,t\)\(\text{energy} = \text{power} \times \text{time}\)\(E\) in J, \(P\) in W, \(t\) in sOn the sheet

\(V_{\mathrm{p}}\,I_{\mathrm{p}} = V_{\mathrm{s}}\,I_{\mathrm{s}}\)transformer: power in = power out\(\mathrm{p}\) = primary, \(\mathrm{s}\) = secondaryOn the sheet

Electric circuits

Summary

Key words

CurrentRate of flow of charge (A)

Potential differenceEnergy per coulomb (V)

ResistanceOpposes current; \(R = V \div I\) (Ω)

Ohmic conductor\(I \propto V\) at constant temperature

SeriesOne loop, same current

ParallelBranches, same p.d.

DiodeCurrent one way only

ThermistorHotter → lower resistance

LDRBrighter → lower resistance

PowerEnergy transferred per second (W)

Alternating currentKeeps reversing direction

Earth wireSafety wire at 0 V; fault current only

Electric circuits

09 Mission 9: Charge that stays put

Static electricity

charging by rubbingattract and repelelectric fields, sparks

AQA spec: Physics 4.2.5Not in Combined Science

KEY RULE

Like charges repel, unlike attract

Mission 9: Static electricity

09 Rub two insulators

Charging by rubbing

Friction moves electrons from one material to the other
Gains electrons → negative
Loses electrons → equally positive
Works for insulators: the charge cannot flow away

“Positive charges move onto the cloth.”

Only electrons move.

Mission 9: Static electricity

Why only electrons?

The positive charge in a material is in the nuclei of its atoms, held deep inside. Electrons on the outside of the atoms are the only charged particles loose enough to be rubbed off.

Why “equally”?

Charge is not created by rubbing, only moved. Every electron the rod gains is one the cloth has lost, so the rod’s negative charge and the cloth’s positive charge are the same size.

Which way do they go?

It depends on the pair of materials. Polythene rubbed with a cloth gains electrons and becomes negative; acetate rubbed with a cloth loses electrons and becomes positive.

A metal rod held in the hand cannot be charged this way: electrons flow through it and through you to earth as fast as they are moved.

09 Forces between charges

Attract or repel

Like charges repel
Unlike charges attract
A non-contact force
Closer together → bigger force

Charged balloon on a wall, hair standing on end, dust on a screen

Mission 9: Static electricity

Engraved plate from 1785 showing a tall glass cylinder with a thin vertical tube on top. Inside, a light horizontal rod with a small ball at one end hangs from a fine thread, near a second fixed ball — Charles-Augustin de Coulomb’s torsion balance, from his 1785 report. Engraving: Charles-Augustin de Coulomb, 1785, public domain

Measured at last

Weighing a push you cannot see

Coulomb hung a light rod from a very thin thread, with a charged ball on one end. A second charged ball pushed it away and twisted the thread. The bigger the force, the bigger the twist.

What he foundHalve the distance between the balls and the force becomes four times as big.

Talk about itWhy did Coulomb need such a thin thread?

Mission 9: Static electricity

09 The space around a charge

Electric fields

A charged object has an electric field around it
Another charge in the field feels a force
Field is strongest close to the object
Lines show the force on a positive charge

Mission 9: Static electricity

Reading the diagram

The lines are closest together at the surface of the sphere and spread out further away. Where the lines are close the field is strong; where they spread, it is weaker.

Drawing one

Draw straight lines that start on the surface, at right angles to it, evenly spaced all the way round. Put an arrowhead part-way along each: pointing away from a positive sphere, towards a negative one.

How a field explains a force without contact

The first object does not need to touch the second. Its field fills the space around it, and the second object feels a force from the field where it is.

Drawing arrows on a negative sphere pointing outwards. The arrows show which way a positive charge would be pushed, so they point in.

09 When the charge escapes

Why sparks jump

Charge builds up on an insulated object
The p.d. to earth and the field grow
Strong enough to ionise the air
Air conducts: electrons jump as a spark

Lightning and car-door shocks are sparks. Aircraft are earthed before refuelling

Mission 9: Static electricity

09 Checkpoint

Quick check

1A rod rubbed with a cloth turns negative. What moved?

Electrons, from the cloth to the rod

2What charge does the cloth now have?

Positive, equal in size

3Two negative balloons: attract or repel?

Repel

4Where is the field around a charged sphere strongest?

Closest to the sphere

5Field lines near a negative sphere point…?

Inwards, towards the sphere

6Why does a spark jump?

Field strong enough to ionise the air

PRESS → TO REVEAL EACH ANSWER

Follow the charge.Track the energy.

Nine missions.

Build & measure

Charge on the move

Energy per coulomb

Resistance &\(V = I\,R\)

Series & parallel

\(I\)–\(V\) characteristics

Power & the Grid

Mains & safety

Static Triple only

Build & measure

No complete loop, no current

A complete loop

Circuit symbols

Draw it properly

Ammeter in series

Charge on the move

Current = charge per second

A rate of flow

Charge flow

Two directions

Current is not used up

Quick check

Energy per coulomb

1 V \(=\) 1 J per coulomb

Potential difference

Voltmeter across

Energy in. Energy out.

Resistance & \(V = I\,R\)

More resistance, less current

Resistance equation

Ohmic conductors

Why metals resist

Measure \(R\)

Length of a wire

\(R \propto\) length

Quick check

Series & parallel

Parallel: same p.d., currents add

Series rules

Parallel rules

Another path, less \(R\)

Find the lamp’s \(R\)

Quick check

\(I\)–\(V\) character­istics

Curved graph, changing \(R\)

Current against p.d.

Lamp & diode

Thermistor & LDR

What they look like

Brighter → more current

Test each component

Reverse & read

Quick check

Power & the National Grid

Power = energy per second

Two power equations

Energy transferred

The National Grid

The Grid, for real

Transformer equation

Quick check

Mains & safety

Switched off ≠ safe

dc vs ac

Three wires, three jobs

Inside a UK plug

Why live is dangerous

Follow the charge.
Track the energy.

Resistance &
\(V = I\,R\)

\(I\)–\(V\) characteristics