KS3 Science Study Pack: Electricity

Key Knowledge: What Electricity Is

Electricity is a way of transferring energy using moving electric charge. In a simple school circuit, the moving charge travels through metal wires and components such as lamps, buzzers, motors and resistors.

An electric circuit must be a complete loop. If there is a gap anywhere in the loop, charge cannot flow all the way round, so the circuit will not work. A complete circuit also needs an energy source, such as a cell or a battery. The energy source provides a voltage, also called a potential difference, which causes charge to move.

A component that transfers electrical energy into another useful form is often called a load. For example:

• a lamp transfers electrical energy into light and thermal energy
• a motor transfers electrical energy into kinetic energy
• a buzzer transfers electrical energy into sound energy
• a resistor transfers electrical energy mainly into thermal energy

In everyday language, people often call a single cell a battery. In science, a battery is two or more cells connected together. A cell has one positive terminal and one negative terminal. When cells are connected in series, their voltages add together.

Electric Circuits and Components

A circuit diagram is a clear drawing that uses standard symbols instead of pictures of real equipment. Circuit diagrams help scientists and engineers understand how components are connected.

A closed switch completes the circuit, so current can flow. An open switch makes a gap, so current cannot flow.

Basic complete circuit

       closed switch
      +----o--o----[ lamp ]----+
      |                        |
      |                        |
    + |                        |
  [ cell ]                     |
    - |                        |
      +------------------------+

The lamp lights because the circuit is complete.

Open and closed circuits

Open circuit: bulb off

      +----o  o----[ lamp ]----+
      |                        |
    [ cell ]                   |
      |                        |
      +------------------------+

Closed circuit: bulb on

      +----o--o----[ lamp ]----+
      |                        |
    [ cell ]                   |
      |                        |
      +------------------------+

Circuit Symbols

Different schools may draw small details of symbols slightly differently, but the meaning is the same.

Component	Simple symbol	Function	Common use
Cell	`+		-`
Battery	`+		- +
Wire	---------	Conducting path for current	Connecting components
Lamp	-(X)-	Transfers electrical energy to light	Torch, indicator light
Open switch	-o o-	Breaks a circuit	Turning a circuit off
Closed switch	-o--o-	Completes a circuit	Turning a circuit on
Resistor	-[ R ]-	Opposes current	Controlling current
Variable resistor	-[ R ]<-	Resistance can be changed	Dimming a lamp, changing motor speed
Motor	-(M)-	Transfers electrical energy to movement	Fan, toy car
Buzzer	-(BZ)-	Transfers electrical energy to sound	Alarm
Ammeter	-(A)-	Measures current	Current investigation
Voltmeter	-(V)-	Measures voltage	Measuring across a component
Fuse	-[ fuse ]-	Melts if current is too high	Plug safety
Diode	`-	>	-`
LED	`-	>	- >>`

Current

Current is the rate of flow of electric charge. It tells us how much charge passes a point in a circuit each second. Current is measured in amperes, with the unit symbol A.

An ammeter measures current. It must be connected in series, so the current flows through the ammeter as part of the same loop.

Correct ammeter placement

      +----( A )----[ lamp ]----[ switch ]----+
      |                                      |
    [ cell ]                                 |
      |                                      |
      +--------------------------------------+

The ammeter is in series with the lamp.

Current is not used up by components. In a simple series circuit, the current is the same at all points. A lamp transfers energy from the moving charge, but the charge continues around the circuit. The cell then transfers energy to the charge again.

In a parallel circuit, the current splits between branches. The total current from the battery is equal to the currents in the branches added together.

Worked Example: Current Is the Same in a Series Circuit

A student measures current before and after a lamp in a series circuit.

Position of ammeter	Current (A)
Before the lamp	0.30
After the lamp	0.30

The readings are the same. This shows that the lamp has not used up current. The lamp transfers electrical energy into light and thermal energy, but the same current flows through every part of the series circuit.

Voltage

Voltage is also called potential difference. It is the energy transferred by each coulomb of charge between two points in a circuit. At KS3, a useful way to think about voltage is: voltage tells us how much energy is available to transfer to components.

Voltage is measured in volts, with the unit symbol V.

A voltmeter measures voltage. It is connected in parallel across a component or across a supply. This is because it compares the energy per unit charge at two different points.

Ammeter and voltmeter placement

          +------( V )------+
          |                 |
      +---+---[ lamp ]------+---[ switch ]---+
      |                                      |
    [ cell ]----( A )------------------------+

The ammeter is in series.
The voltmeter is in parallel across the lamp.

In a series circuit, the supply voltage is shared between components. If two identical lamps are connected in series to a 6 V battery, each lamp may get about 3 V.

In a parallel circuit, each branch gets the full supply voltage. If two identical lamps are connected in parallel to a 6 V battery, each lamp has 6 V across it.

Voltage does not flow. Current flows. Voltage is a difference between two points.

Resistance

Resistance is how much a component or material opposes current. Resistance is measured in ohms, written as ohm.

A high resistance means it is harder for current to flow. A low resistance means current can flow more easily. A resistor is a component designed to have a particular resistance. A variable resistor can be adjusted to change the current in a circuit.

Resistance can be affected by:

• the material used
• the length of a wire
• the thickness of a wire
• the temperature of a component
• the type of component

For a fixed voltage, increasing resistance decreases current. For a fixed resistance, increasing voltage increases current.

Current, Voltage and Resistance

Quantity	Meaning	Unit	Measuring instrument	How to connect the instrument
Current, I	Rate of flow of electric charge	ampere (A)	Ammeter	In series
Voltage, V	Energy transferred per coulomb of charge between two points	volt (V)	Voltmeter	In parallel
Resistance, R	How much a component opposes current	ohm	Calculated from voltage and current, or measured by some meters	Component is tested in a circuit

Equation

Equation form	Use
V = I x R	Find voltage when current and resistance are known
I = V / R	Find current when voltage and resistance are known
R = V / I	Find resistance when voltage and current are known

In these equations:

• V is voltage in volts (V)
• I is current in amperes (A)
• R is resistance in ohms (ohm)

Worked Example: Finding Current

A 12 ohm resistor is connected to a 6 V battery. Find the current.

Equation:

I = V / R

Substitution:

I = 6 V / 12 ohm

Calculation:

I = 0.5 A

The current is 0.5 A.

Worked Example: Finding Resistance

A resistor has 3 V across it and a current of 0.20 A through it. Find the resistance.

Equation:

R = V / I

Substitution:

R = 3 V / 0.20 A

Calculation:

R = 15 ohm

The resistance is 15 ohm.

Worked Example: Finding Voltage

A current of 0.40 A flows through a 10 ohm resistor. Find the voltage across it.

Equation:

V = I x R

Substitution:

V = 0.40 A x 10 ohm

Calculation:

V = 4 V

The voltage is 4 V.

Worked Example: Cells in Series

Three 1.5 V cells are connected in series.

Total voltage:

1.5 V + 1.5 V + 1.5 V = 4.5 V

The battery supplies 4.5 V.

Conductors and Insulators

A conductor is a material that allows current to flow easily. Metals, such as copper and aluminium, are good conductors. In simple KS3 terms, metals conduct well because they contain charged particles that can move through the metal.

An insulator is a material that does not allow current to flow easily. Plastic, rubber, glass and dry wood are insulators. They have very high resistance, so very little current flows through them in ordinary conditions.

Wires often have a copper core covered by plastic insulation. The copper conducts current around the circuit. The plastic stops current flowing into people or nearby objects.

Type of material	Examples	Property	Uses
Conductor	Copper, aluminium, steel, graphite	Allows current to flow easily	Wires, plugs, contacts
Insulator	Plastic, rubber, glass, dry wood, ceramic	Does not allow current to flow easily	Cable covering, switch cases, plug cases

Conductor and Insulator Testing Circuit

Testing a material sample

      +----[ lamp ]----o     o----+
      |              test gap     |
      |                           |
    [ cell ]----[ switch ]--------+

Place a material across the gap.
If the lamp lights, the material is a conductor.
If the lamp does not light, the material is an insulator.

Series Circuits

A series circuit has one loop. All components are connected one after another along the same path.

Series circuit with two lamps

      +----[ lamp 1 ]----[ lamp 2 ]----[ switch ]----+
      |                                             |
    [ battery ]                                     |
      |                                             |
      +---------------------------------------------+

Important facts about series circuits:

• There is only one path for current.
• The current is the same through each component.
• The supply voltage is shared between components.
• Adding more components increases the total resistance.
• If one component breaks, the whole circuit stops working.
• Identical lamps in series usually have the same brightness.

Worked Example: Adding a Second Bulb in Series

A circuit has one lamp connected to a battery. The lamp is bright. A second identical lamp is added in series.

Prediction:

• The total resistance increases.
• The current decreases.
• The battery voltage is shared between two lamps.
• Both lamps are dimmer than the original single lamp.

The first lamp is not brighter because it is closer to the battery. In a series circuit, identical lamps have the same current and usually the same brightness.

Worked Example: Is the Circuit Open or Closed?

      +----o  o----[ lamp ]----+
      |                        |
    [ cell ]                   |
      |                        |
      +------------------------+

The switch is open, so there is a gap in the circuit. Current cannot flow around the complete loop. The lamp does not light.

Parallel Circuits

A parallel circuit has more than one loop or branch. Current can take different paths through the circuit.

Parallel circuit with two lamps

          +----[ lamp 1 ]----+
          |                  |
      +---+                  +---[ switch ]---+
      |   |                  |                |
    [ battery ]              |                |
      |   +----[ lamp 2 ]----+                |
      |                                      |
      +--------------------------------------+

Important facts about parallel circuits:

• There is more than one path for current.
• Current splits at a junction and rejoins later.
• Each branch gets the full supply voltage.
• The total current from the battery is the branch currents added together.
• If one branch is broken, other branches can still work.
• Homes use parallel circuits because appliances and lights need to work independently.

Current splitting and rejoining

                 branch current 0.20 A
              +--------[ lamp 1 ]--------+
              |                          |
total 0.50 A  |                          | total 0.50 A
----->--------+                          +-------->
              |                          |
              +--------[ lamp 2 ]--------+
                 branch current 0.30 A

0.20 A + 0.30 A = 0.50 A

Worked Example: Adding a Second Bulb in Parallel

A circuit has one lamp connected to a 6 V battery. A second identical lamp is added in parallel.

Prediction:

• Each lamp still has 6 V across it.
• Each lamp can be about as bright as the original single lamp.
• The total current from the battery increases because there are now two branches.
• If one lamp fails, the other lamp can still light.

Parallel circuits are not simply "stronger". Their behaviour is explained by each branch receiving the full supply voltage and the current splitting between branches.

Series and Parallel Compared

Feature	Series circuit	Parallel circuit
Number of loops	One loop	Two or more loops or branches
Current	Same everywhere	Splits between branches
Voltage	Shared between components	Full supply voltage across each branch
Adding identical lamps	Lamps become dimmer	Lamps can stay about as bright as one lamp
One lamp fails	Whole circuit stops	Other branches can still work
Household use	Not suitable for most home lighting	Useful because appliances work independently

Measuring Electricity in Practical Work

Good practical work means collecting evidence carefully and using it to support a conclusion.

When measuring electricity:

• connect the ammeter in series
• connect the voltmeter in parallel across the component being tested
• check that wires are connected firmly
• use the correct meter range if the meter has ranges
• record units in table headings
• repeat readings when useful
• calculate means when repeat readings are close enough
• switch off between readings if components become warm

Accuracy means how close a measurement is to the true value. Precision means how small the scale divisions are, or how closely repeated measurements agree. Repeatability means getting similar results when the same person repeats the same method with the same equipment. Reliability improves when results are repeated and checked.

Full Practical Investigation: How Does Voltage Affect Current Through a Resistor?

Aim

Investigate the relationship between voltage and current for a resistor.

Apparatus

• low-voltage school power supply or cells
• switch
• fixed resistor
• ammeter
• voltmeter
• connecting wires
• optional variable resistor

Circuit Setup

          +------( V )------+
          |                 |
      +---+---[ resistor ]--+---[ switch ]---+
      |                                      |
 [ low-voltage supply ]----( A )-------------+

The ammeter is in series so it measures current through the resistor. The voltmeter is in parallel across the resistor so it measures voltage across the resistor.

Variables

Variable type	Variable in this investigation
Independent variable	Voltage supplied to the resistor
Dependent variable	Current through the resistor
Control variables	Same resistor, same circuit setup, similar temperature where possible, same meters

Method

1. Build the circuit shown in the diagram using low-voltage school equipment.
2. Check that the ammeter is in series and the voltmeter is in parallel across the resistor.
3. Set the supply to a low voltage, such as 1 V.
4. Close the switch and record the voltage and current.
5. Open the switch between readings if the resistor becomes warm.
6. Increase the voltage in equal steps, such as 1 V each time.
7. Record the current for each voltage.
8. Repeat each reading if there is time.
9. Calculate a mean current if the repeated readings are close.
10. Plot a graph with voltage on the x-axis and current on the y-axis.

Safety

• Use low-voltage school equipment only.
• Do not use mains electricity.
• Check that wires are not damaged.
• Switch off if the resistor or wires become warm.
• Tell the teacher if a component smells hot, sparks or looks damaged.

Results Table

Voltage across resistor (V)	Current repeat 1 (A)	Current repeat 2 (A)	Current repeat 3 (A)	Mean current (A)
1.0	0.10	0.10	0.11	0.10
2.0	0.20	0.21	0.20	0.20
3.0	0.31	0.30	0.30	0.30
4.0	0.40	0.41	0.40	0.40
5.0	0.50	0.50	0.51	0.50

Graph Instructions

Plot voltage on the x-axis and current on the y-axis. If the points form a straight line through or near the origin, current is directly proportional to voltage. This means that doubling the voltage doubles the current. The resistor has approximately constant resistance if its temperature does not change much.

Conclusion Prompt

Describe the pattern in the results. Use values from the table. Link the pattern to resistance.

Example conclusion: As voltage increased from 1.0 V to 5.0 V, the mean current increased from 0.10 A to 0.50 A. When the voltage doubled from 2.0 V to 4.0 V, the current also doubled from 0.20 A to 0.40 A. This suggests current is directly proportional to voltage for this resistor, so the resistance stayed approximately constant.

Evaluation Prompt

Comment on:

• whether repeated readings were close together
• whether there were anomalies
• whether loose connections could affect readings
• whether the resistor heated up
• whether the meters were precise enough
• how the method could be improved

Possible improvements include taking more repeats, using digital meters, switching off between readings, checking connections before each reading, and using a variable resistor or power supply to change voltage more smoothly.

Short Practical: Testing Conductors and Insulators

Build a circuit with a cell, switch, lamp or buzzer, and a gap. Place different materials in the gap.

Material tested	Bulb lights?	Conductor or insulator?
Copper coin	Yes	Conductor
Plastic ruler	No	Insulator
Aluminium foil	Yes	Conductor
Rubber band	No	Insulator
Steel paper clip	Yes	Conductor
Dry wooden splint	No	Insulator

Independent variable: material placed in the gap.

Dependent variable: whether the bulb lights.

Control variables: same circuit, same cell, same lamp, same size of gap, clean contact points.

Data and Graph Skills

Data Task 1: Calculating Resistance from Results

A student measured current through a resistor at different voltages.

Voltage (V)	Current (A)	Resistance, R = V / I (ohm)
1.0	0.10	10
2.0	0.20	10
3.0	0.30	10
4.0	0.25	16
5.0	0.50	10

Questions:

1. Describe the pattern for most of the results.
2. Which reading is anomalous?
3. Calculate the resistance at 2.0 V.
4. Suggest one reason for the anomalous reading.
5. Suggest one improvement to make the results more reliable.

The main pattern is that voltage and current increase together, giving a resistance of about 10 ohm. The 4.0 V reading is anomalous because the current should be about 0.40 A for a 10 ohm resistor, not 0.25 A. A loose connection, misread meter or recording error could cause this. Repeating readings would help check reliability.

Data Task 2: Graph Interpretation

A current-voltage graph for a resistor has these plotted points:

Voltage (V)	Current (A)
0	0.00
1	0.05
2	0.10
3	0.15
4	0.20
5	0.25

Questions:

1. Describe the relationship between voltage and current.
2. Estimate the current at 6 V if the pattern continues.
3. Is the resistance approximately constant? Explain.
4. Calculate the resistance at 4 V.

Model interpretation: The current increases by 0.05 A for every 1 V increase. The graph would be a straight line through the origin, so current is directly proportional to voltage. At 6 V, the current would be about 0.30 A. At 4 V, R = 4 V / 0.20 A = 20 ohm, so the resistance is approximately constant.

Data Task 3: Bulb Brightness

Circuit	Current from battery (A)	Voltage across each bulb (V)	Brightness
One bulb	0.40	6.0	Bright
Two identical bulbs in series	0.20	3.0	Dim
Two identical bulbs in parallel	0.80 total	6.0	Both bright

Questions:

1. Why are the two series bulbs dimmer?
2. Why are the two parallel bulbs bright?
3. Which circuit draws the largest total current from the battery?

In series, total resistance is higher and the supply voltage is shared, so each bulb has less voltage across it and the current is lower. In parallel, each bulb has the full 6.0 V across it, so each can be as bright as a single bulb. The parallel circuit draws the largest total current because the branch currents add together.

Data Task 4: Current Splitting in Parallel Circuits

Total current from battery (A)	Branch 1 current (A)	Branch 2 current (A)	Branch 3 current (A)
0.60	0.20	0.40	-
0.90	0.30	0.30	0.30
1.20	0.50	0.40	0.30
0.75	0.25	?	0.20

For the final row:

Branch 2 current = 0.75 A - 0.25 A - 0.20 A = 0.30 A

The total current equals the sum of the branch currents.

Electrical Safety

Mains electricity can be dangerous because it has a much higher voltage than school cell circuits. In the UK, mains electricity is about 230 V. This can cause a large current through the body, which can be fatal. Low-voltage school circuits are much safer, but they still need careful use because components can become warm and damaged wires can cause short circuits.

Safety features are based on scientific ideas about current, resistance, heating and insulation.

Simple plug and cable safety diagram

       plug outer case
     +----------------+
     |                |
     |   [ fuse ]     |  fuse melts if current is too high
     |      |         |
     +------|---------+
            |
      cable outer insulation
     ========================
      copper conductor inside
     ------------------------
      plastic insulation around conductor

Hazard	Possible danger	Safety feature	Scientific explanation
Damaged cable insulation	Exposed conductor could give an electric shock	Plastic or rubber insulation	Insulators have very high resistance and stop current flowing into people
Too many appliances in one extension lead	Wires may overheat	Correctly rated extension lead and fuse	Large current causes heating in wires
Water near mains electricity	Electric shock risk	Keep appliances away from water	Impure water can conduct, and wet skin has lower resistance
Fault inside an appliance	Metal case may become live	Fuse, circuit breaker, earthing where used	A large fault current can break the circuit quickly
Wrong fuse rating	Cable may overheat before fuse melts	Correct fuse rating	Fuse wire heats and melts when current is too high
Broken phone charging cable	Exposed conductors and short circuits	Replace damaged cable	Conductors touching can make a low-resistance path and high current

How a Fuse Works

A fuse contains a thin piece of wire. If the current is too high, the fuse wire heats up and melts. This breaks the circuit, so current stops flowing. A fuse helps protect wiring and appliances from excessive current. It does not remove all electrical risks and does not guarantee that a person cannot get an electric shock.

Worked Example: Why a Fuse Melts

A toaster develops a fault and the current becomes too high. The fuse wire has resistance, so the large current makes it heat up. When it gets hot enough, the fuse wire melts and breaks the circuit. This stops the current and reduces the chance of the cable or appliance overheating.

Safety Case Studies

Overloaded Extension Lead

An extension lead has a kettle, toaster and heater plugged into it. These are high-power appliances, so they transfer energy quickly and need large currents. If too many are used at once, the total current may be too high. The wires can heat up, insulation can melt, and a fire could start. A suitable fuse or circuit breaker should disconnect the circuit if the current is too high, but the safer choice is not to overload the extension lead.

Wet Bathroom or Kitchen Hazard

Water and mains electricity are dangerous together. Tap water is not pure and can conduct electricity. Wet skin has lower resistance than dry skin, so a larger current can pass through the body. Electrical appliances should be kept away from baths, sinks and wet surfaces.

Broken Phone Charging Cable

A broken charging cable may have damaged insulation and exposed conductors. If conductors touch each other, there may be a short circuit with very low resistance and a large current. If a person touches exposed conductors, there may be a shock risk, especially if the charger or socket is unsafe. Damaged cables should be replaced.

Real-World Examples

Torch

A torch has cells, a switch, metal contacts and a lamp or LED. When the switch is closed, the circuit is complete and current flows. The lamp or LED transfers electrical energy into light. If the cells are flat, they cannot provide enough voltage, so the torch is dim or off.

Bike Light

A bike light often uses cells, LEDs and switches. LEDs are useful because they transfer electrical energy into light efficiently. Some bike lights have more than one LED connected so that the light remains bright and visible.

Phone Charger

A phone charger transfers electrical energy from the mains supply to the phone battery. The battery stores energy chemically. Chargers and cables must have safe insulation because they are connected to a high-voltage supply at the plug end.

Household Lighting

Home lighting uses parallel circuits so that each lamp can receive the correct voltage and work independently. If one lamp fails, other lamps can still work. This is much more useful than a series circuit, where one broken lamp would stop the whole loop.

High-Power Appliances

Kettles, toasters and hairdryers transfer electrical energy quickly. They need larger currents than small devices such as LED lights. Their plugs, cables and fuses must be suitable for the current they use.

Common Misconceptions

Misconception	Correct scientific idea
Current gets used up as it moves around a circuit.	Current is the same at all points in a simple series circuit. Energy is transferred, not current.
A cell makes current only at one end.	A cell provides a voltage across the whole circuit, causing charge to flow around a complete loop.
Voltage flows around a circuit.	Voltage is a difference in energy per unit charge between two points. Current flows.
A bulb closer to the battery is brighter in series.	Identical bulbs in series have the same current and usually the same brightness.
Current is faster after a battery and slower after a bulb.	In a working series circuit, the current is the same everywhere.
A bigger battery is always safer or better.	Higher voltage can produce larger current, more heating, damaged components and greater risk.
Parallel circuits are "stronger".	Each branch has the full supply voltage, and current splits between branches.
Ammeters and voltmeters can be connected anywhere.	Ammeters go in series. Voltmeters go in parallel across a component.
Resistance stops electricity completely.	Resistance opposes current. Insulators have very high resistance; resistors allow some current.
All metals conduct equally well.	Metals conduct well, but different metals have different resistances.
Plastic on wires helps electricity flow.	Plastic is an insulator that helps stop current flowing into people or objects.
School circuits and mains electricity are equally dangerous.	School circuits are low voltage. Mains electricity can be fatal.
Fuses stop all electric shocks.	Fuses protect wiring and appliances from excessive current but do not remove all risks.

Worked Example: Drawing a Circuit Diagram from a Description

Description: Draw a circuit with a battery, switch, lamp and ammeter all in series, with a voltmeter across the lamp.

Step 1: Put the battery, ammeter, lamp and switch in one loop.

Step 2: Add the voltmeter in a separate small loop across the lamp only.

          +------( V )------+
          |                 |
      +---+---[ lamp ]------+---[ switch ]---+
      |                                      |
    [ battery ]----( A )---------------------+

Check:

• The ammeter is in series.
• The voltmeter is in parallel across the lamp.
• The switch can open or close the whole circuit.
• The battery provides the voltage.

Exam-Style Questions

Multiple-Choice Questions

1. What is needed for current to flow in a simple circuit? A. A complete conducting loop and an energy source
   B. A lamp and a plastic wire
   C. An open switch and a cell
   D. A voltmeter connected in series only

2. Which statement about current in a series circuit is correct? A. Current is used up by the first lamp
   B. Current is the same at all points
   C. Current is larger after the battery and zero after the lamp
   D. Current only flows through the brightest component

3. What does a voltmeter measure? A. Resistance
   B. Current
   C. Potential difference
   D. Temperature

4. How should an ammeter be connected? A. In parallel across a component
   B. In series with the component
   C. Across the battery only
   D. Outside the circuit

5. Which material is usually a good conductor? A. Rubber
   B. Plastic
   C. Copper
   D. Glass

6. Two identical bulbs are added in series to a battery. What happens compared with one bulb? A. Each bulb becomes brighter
   B. The current increases
   C. The bulbs become dimmer
   D. The battery voltage disappears

7. Why are home lights usually connected in parallel? A. So current is used up by each lamp
   B. So each lamp can work independently
   C. So one failed lamp turns off every lamp
   D. So each lamp gets no voltage

8. What is resistance? A. The rate of flow of charge
   B. Energy transferred per coulomb
   C. How much a component opposes current
   D. The brightness of a lamp

9. A 6 V battery is connected across a 3 ohm resistor. What is the current? A. 0.5 A
   B. 2 A
   C. 9 A
   D. 18 A

10. Why is plastic used around copper wires? A. It is a conductor that increases current
    B. It is an insulator that improves safety
    C. It stores voltage
    D. It makes current get used up

Short-Answer Questions

1. Define current and give its unit.
2. Define voltage and give its unit.
3. Define resistance and give its unit.
4. Explain the difference between an open circuit and a closed circuit.
5. Explain why current is not used up by a lamp.
6. Describe how voltage is shared in a series circuit.
7. Describe what happens to current at a junction in a parallel circuit.
8. Explain why a broken lamp in one branch of a parallel circuit does not stop all branches working.
9. State one conductor and one insulator, and describe a use for each.
10. Explain why water near mains electricity is dangerous.

Calculation Questions

1. A resistor has 10 V across it and a current of 2 A through it. Calculate the resistance.
2. A 20 ohm resistor has a current of 0.30 A through it. Calculate the voltage.
3. A 4 ohm resistor is connected to an 8 V supply. Calculate the current.
4. Four 1.5 V cells are connected in series. Calculate the total voltage.
5. A parallel circuit has branch currents of 0.25 A, 0.35 A and 0.40 A. Calculate the total current from the battery.

Diagram Interpretation Questions

Use this circuit:

          +------( V )------+
          |                 |
      +---+---[ lamp ]------+---o--o---+
      |                                  |
    [ cell ]----( A )-------------------+

1. Is the switch open or closed?
2. Will the lamp light? Explain.
3. Is the ammeter correctly connected?
4. Is the voltmeter correctly connected?
5. What must be changed to make the lamp light?

Use this circuit:

          +----[ lamp 1 ]----+
          |                  |
      +---+                  +---+
      |   |                  |   |
    [ battery ]              |   |
      |   +----[ lamp 2 ]----+   |
      |                          |
      +--------------------------+

1. Is this circuit series or parallel?
2. If lamp 1 fails and its branch is broken, can lamp 2 still light?
3. Does each branch receive the full supply voltage?
4. If lamp 1 current is 0.20 A and lamp 2 current is 0.30 A, what is the total current?

Practical Planning Question

Plan an investigation to answer this question:

How does changing the number of cells affect the current through a resistor?

In your answer, include:

• the independent variable
• the dependent variable
• at least three control variables
• a brief method
• how to make the test fair
• one safety point
• how to improve reliability

Practical Evaluation Question

A student measures current through a resistor three times at the same voltage.

Repeat	Current (A)
1	0.42
2	0.43
3	0.37

1. Which reading may be anomalous?
2. What is one possible cause?
3. Should the student calculate the mean using all three readings? Explain.
4. Suggest two improvements to the method.

Safety Stimulus Question

A student sees an extension lead under a desk. It has a kettle, heater and phone charger plugged in. The cable insulation is cracked near the plug, and the extension lead is next to a wet floor.

1. Identify three hazards.
2. Explain the scientific reason each hazard is dangerous.
3. Name one safety feature that can break a circuit if current is too high.
4. Explain why the safest action is to stop using the extension lead and tell an adult.

Longer 6-8 Mark Question

Compare series and parallel circuits for lighting a home. In your answer, explain:

• number of loops or branches
• current
• voltage
• bulb brightness
• what happens if one lamp fails
• why one circuit type is more suitable for homes

Model Answers

Multiple-Choice Answers

1. A
2. B
3. C
4. B
5. C
6. C
7. B
8. C
9. B
10. B

Short-Answer Model Answers

1. Current is the rate of flow of electric charge. It is measured in amperes (A).
2. Voltage, or potential difference, is the energy transferred by each coulomb of charge between two points. It is measured in volts (V).
3. Resistance is how much a component opposes current. It is measured in ohms (ohm).
4. A closed circuit is complete, so current can flow. An open circuit has a gap, so current cannot flow.
5. A lamp transfers electrical energy into light and thermal energy. It does not use up current. In a series circuit, the same current flows before and after the lamp.
6. In a series circuit, the supply voltage is shared between components. More components means each may get a smaller share of the voltage.
7. At a junction in a parallel circuit, current splits between branches. The branch currents add together when they rejoin.
8. In a parallel circuit, each branch is a separate path. If one branch is broken, current can still flow through another complete branch.
9. Copper is a conductor and is used in wires because current flows through it easily. Plastic is an insulator and is used around wires to reduce shock risk.
10. Tap water can conduct electricity and wet skin has lower resistance, so a dangerous current may pass through the body near mains electricity.

Calculation Model Answers

1. R = V / I = 10 V / 2 A = 5 ohm
2. V = I x R = 0.30 A x 20 ohm = 6 V
3. I = V / R = 8 V / 4 ohm = 2 A
4. 1.5 V + 1.5 V + 1.5 V + 1.5 V = 6.0 V
5. 0.25 A + 0.35 A + 0.40 A = 1.00 A

Diagram Model Answers

For the first diagram:

1. The switch is open.
2. The lamp will not light because the circuit has a gap.
3. The ammeter is correctly connected in series.
4. The voltmeter is correctly connected in parallel across the lamp.
5. Close the switch to complete the circuit.

For the second diagram:

1. It is a parallel circuit because there is more than one branch.
2. Yes. Lamp 2 can still light if its branch is complete.
3. Yes. Each branch receives the full supply voltage.
4. 0.20 A + 0.30 A = 0.50 A

Practical Planning Model Answer

Independent variable: number of cells.

Dependent variable: current through the resistor.

Control variables: same resistor, same ammeter, same wires and circuit arrangement, similar temperature, same switch position during readings.

Method: Build a series circuit with cells, a switch, an ammeter and a resistor. Start with one cell and record the current. Add a second cell in series and record the current again. Continue for a safe number of cells agreed by the teacher. Repeat each reading and calculate a mean if the repeats are close. Keep the same resistor and circuit setup each time.

Fair testing: Change only the number of cells. Keep other variables the same.

Safety: Use low-voltage school cells only and switch off if the resistor becomes warm.

Reliability: Repeat readings, check for anomalies, and make sure all connections are firm.

Practical Evaluation Model Answer

The 0.37 A reading may be anomalous because it is lower than 0.42 A and 0.43 A. A loose connection, meter reading error or changing temperature could have caused it. The student should not simply calculate a mean using all three readings without checking, because the anomalous result would make the mean less representative. The student should repeat the measurement, check connections, use the same meter range, and switch off between readings if the resistor warms up.

Safety Stimulus Model Answer

Hazards include too many high-power appliances in one extension lead, cracked insulation, and water nearby. The kettle and heater may cause a large total current, which can heat wires and possibly cause a fire. Cracked insulation can expose conductors, increasing the risk of electric shock or short circuit. Water can conduct electricity and wet skin has lower resistance, making electric shock more likely. A fuse or circuit breaker can break the circuit if current is too high. The safest action is to stop using the extension lead and tell an adult because mains electricity can be fatal.

Longer 6-8 Mark Model Answer

A series circuit has one loop, so the same current flows through every lamp. The supply voltage is shared between the lamps, so adding more lamps usually makes them dimmer. If one lamp fails or is removed, the circuit is broken and all lamps go out. This would be unsuitable for home lighting.

A parallel circuit has more than one branch. Current from the supply splits between branches and then rejoins. Each branch receives the full supply voltage, so each lamp can work at normal brightness. If one lamp fails, other branches can still be complete, so other lamps can stay on. Homes use parallel circuits because lights and appliances need to work independently and receive the correct voltage.

Key Vocabulary

Term	Meaning
Ammeter	Instrument used to measure current; connected in series
Ampere (A)	Unit of current
Battery	Two or more cells connected together
Cell	Energy source that provides voltage to a circuit
Circuit	Complete loop that allows charge to flow
Closed circuit	Complete circuit with no gap
Conductor	Material that allows current to flow easily
Current	Rate of flow of electric charge
Diode	Component that allows current mainly one way
Fuse	Safety component that melts and breaks a circuit if current is too high
Insulator	Material that does not allow current to flow easily
LED	Light-emitting diode
Load	Component that transfers electrical energy to another form
Open circuit	Circuit with a gap, so current cannot flow
Parallel circuit	Circuit with more than one branch
Potential difference	Another name for voltage
Resistance	How much a component opposes current
Resistor	Component designed to have resistance
Series circuit	Circuit with one loop
Variable resistor	Resistor whose resistance can be changed
Volt (V)	Unit of voltage
Voltage	Energy transferred per coulomb of charge between two points
Voltmeter	Instrument used to measure voltage; connected in parallel

Revision Summary

Facts to Know

• A circuit must be a complete loop for current to flow.
• A cell provides voltage; a battery is two or more cells.
• Current is the rate of flow of electric charge, measured in amperes (A).
• Voltage is energy transferred per coulomb between two points, measured in volts (V).
• Resistance is opposition to current, measured in ohms (ohm).
• V = I x R, I = V / R, and R = V / I.
• An ammeter is connected in series.
• A voltmeter is connected in parallel.
• Current is not used up by components.
• Conductors allow current to flow easily.
• Insulators do not allow current to flow easily.
• Metals conduct because they contain charged particles that can move.
• Plastic insulation around copper wires helps prevent electric shock.

Circuit Behaviour to Know

• Series circuits have one loop.
• In series, current is the same everywhere.
• In series, voltage is shared between components.
• Adding lamps in series increases resistance and makes lamps dimmer.
• If one part of a series circuit breaks, the whole circuit stops.
• Parallel circuits have more than one branch.
• In parallel, current splits between branches.
• In parallel, each branch gets the full supply voltage.
• Adding lamps in parallel increases total current from the battery.
• If one branch breaks in a parallel circuit, other branches can still work.

Working Scientifically Checklist

• Identify the independent variable: the variable changed.
• Identify the dependent variable: the variable measured.
• Identify control variables: variables kept the same.
• Use a fair test by changing only one independent variable.
• Record units in table headings.
• Repeat readings to check repeatability.
• Calculate means when repeated readings are close.
• Look for anomalies.
• Use evidence from data to support conclusions.
• Comment on accuracy, precision, reliability and improvements.

Electrical Safety Checklist

• Mains electricity is much more dangerous than low-voltage school circuits.
• Damaged insulation can expose conductors.
• Water and mains electricity are dangerous together.
• Too much current can heat wires and cause fires.
• Fuses melt and break the circuit if current is too high.
• Circuit breakers can switch off circuits when faults happen.
• Earthing can help make metal-cased appliances safer where it is used.
• Never use damaged cables, overloaded sockets or electrical devices near water.

Final Self-Test

You are ready for this topic if you can:

• draw and recognise common circuit symbols
• explain open and closed circuits
• connect ammeters and voltmeters correctly
• compare current and voltage in series and parallel circuits
• predict bulb brightness when components are added
• calculate current, voltage or resistance using V = I x R
• classify materials as conductors or insulators
• interpret tables and graphs from electricity investigations
• identify variables in a practical method
• evaluate repeatability, reliability, accuracy and precision
• explain electrical safety using current, resistance, heating and insulation