Physical Science Enhancement - Physics 3 - Circuits and resistivity
Introduction
Electric circuits power almost every modern device, from phones to refrigerators. In this unit you will learn how current, voltage, and resistance behave in series and parallel circuits, apply Ohm’s law, and investigate resistivity and potential dividers. You will finish by designing and testing a sensing circuit using real components.
Content
PS3.1 — Introduction to current, voltage and circuit symbols
In Unit 2 you studied how energy is stored and transferred in mechanical systems. In this unit we shift focus to electrical circuits, the foundation of modern technology. Today you will learn what current and voltage mean, how they are measured, and how to represent circuits using standard symbols.
Objectives
- Define electric current as the flow of charge.
- Define voltage as the energy transferred per unit charge.
- Identify and use common circuit symbols to draw simple diagrams.
- Measure current with an ammeter and voltage with a voltmeter.
Key Ideas & Example
Current (I): flow of electric charge, measured in amperes (A).
Voltage (V): potential difference, energy transferred per coulomb of charge, measured in volts (V).
Resistance (R): how much a component opposes current, measured in ohms (Ω).
Example: A lamp connected to a 6 V battery has a current of 0.3 A. The resistance is R = V/I = 6 ÷ 0.3 = 20 Ω.
Activity — Building and measuring a simple circuit
Apparatus and materials
- Cell (1.5 V or 6 V battery pack).
- Lamp or resistor.
- Switch, connecting wires.
- Ammeter, voltmeter (or multimeters).
- Worksheet with circuit symbols and practice diagrams.
Procedure (30-minute working window)
- Review circuit symbols as a class (cell, battery, lamp, switch, resistor, ammeter, voltmeter).
- In pairs, draw a diagram for a simple series circuit (cell + lamp + switch).
- Build the circuit using wires and components.
- Measure current with the ammeter in series and voltage across the lamp with the voltmeter in parallel.
- Record readings, sketch the final circuit with correct symbols and labelled measurements.
Safety
- Use low-voltage cells only (max 6 V).
- Do not short-circuit the battery pack.
- Switch off circuits when not in use to avoid heating components.
Discussion prompts
- How are current and voltage different?
- Why is it important to use standard symbols in circuit diagrams?
- What do your ammeter and voltmeter readings tell you about energy transfer in the circuit?
Summary
- Current is the flow of charge; voltage is the energy transferred per charge.
- Ammeter is connected in series; voltmeter in parallel.
- Circuit symbols provide a universal language to describe circuits.
Check your understanding
1) What does an ammeter measure, and how is it connected?
2) What does a voltmeter measure, and how is it connected?
3) Why are standard circuit symbols useful?
Teacher guidance
- Timing (40 min): 5 settle/intro → 10 symbols + diagram practice → 30 build and measure circuit → 5 clear/wrap-up.
- Setup: Prepare trays with all required components. Have worksheet with circuit symbols ready.
- Focus: Students must connect meters correctly and match diagrams to real circuits.
- Differentiation: Strong groups can calculate resistance (R = V/I). Struggling groups focus only on using meters correctly.
- Exit ticket: “In one sentence, explain the difference between current and voltage.”
- Next lesson: Introduce Ohm’s law (V = IR) and use it in both experiments and calculations.
PS3.2 — Ohm’s Law
Last lesson you built simple series circuits and measured current and voltage. Today you will investigate the relationship between voltage, current, and resistance, and learn how to apply Ohm’s Law in both experiments and calculations.
Objectives
- State Ohm’s Law: V = IR.
- Measure current and voltage in a circuit and show they are proportional.
- Plot and interpret an I–V graph for a resistor.
- Use Ohm’s Law to calculate resistance, current, or voltage.
Key Ideas & Example
Ohm’s Law: For a resistor at constant temperature, voltage across it is proportional to current through it.
Formula: V = IR, where V = potential difference (V), I = current (A), R = resistance (Ω).
Example: A lamp has a current of 0.40 A when connected to 8.0 V. Resistance = V/I = 8.0 ÷ 0.40 = 20 Ω.
Activity — Investigating Ohm’s Law
Apparatus and materials
- Battery pack (6 V) or low-voltage power supply.
- Resistor (or lamp) + variable resistor.
- Ammeter, voltmeter (or multimeters).
- Connecting wires, switch.
- Graph paper or spreadsheet.
Procedure (30-minute working window)
- Set up circuit with resistor, variable resistor, ammeter in series, and voltmeter in parallel.
- Vary resistance to change current. Record 5–6 pairs of current (I) and voltage (V).
- Plot V against I on graph paper. Draw best-fit line through the origin.
- Calculate gradient to find resistance R (since R = V/I).
- Extension: Repeat with a lamp. Observe non-linear graph (resistance increases as filament heats).
Safety
- Use low voltages only (max 6 V).
- Do not leave lamp connected for long periods to avoid overheating.
- Switch off when not recording measurements.
Discussion prompts
- What does the straight-line graph for a resistor show?
- Why is the I–V graph for a lamp curved rather than straight?
- How can you use V = IR to calculate missing quantities?
Summary
- Ohm’s Law states that V is proportional to I for a resistor at constant temperature.
- Resistance can be calculated from the gradient of a V–I graph.
- Real components like lamps may deviate from Ohm’s Law due to heating effects.
Check your understanding
1) A 12 V supply produces a 3.0 A current. What is the resistance?
2) If a resistor is 50 Ω and the current is 0.20 A, what is the voltage across it?
3) Why does a lamp’s resistance increase as it gets hotter?
Teacher guidance
- Timing (40 min): 5 settle/recap → 10 demo/setup → 30 student data collection + graph → 5 clear/wrap-up.
- Setup: Check variable resistors and meters before class. Prepare spare resistors in case of overheating.
- Focus: Students must connect meters correctly and plot clean V–I graphs. Reinforce that resistance = gradient.
- Differentiation: Strong groups calculate resistance at multiple points for non-linear lamp. Struggling groups just do resistor straight line.
- Exit ticket: “What is Ohm’s Law in words?”
- Next lesson: Apply V = IR to analyse current and voltage in series circuits.
PS3.3 — Series circuits
Last lesson you investigated Ohm’s Law and plotted I–V graphs for resistors and lamps. Today you will extend this by analysing series circuits: how current and voltage behave, and how resistance adds up when components are connected one after another.
Objectives
- Describe current and voltage in series circuits.
- Use the formula Rtotal = R1 + R2 + R3.
- Measure and record current and voltage in series circuits with 2–3 resistors.
- Explain how potential difference is shared across components.
Key Ideas & Example
Current in series: Same through all components.
Voltage in series: Shared between components; sum of voltages = supply voltage.
Resistance in series: Rtotal = R1 + R2 + R3.
Example: A 6 V supply is connected to two equal resistors in series. Current = 0.20 A. Each resistor gets 3 V, so R = V/I = 3 ÷ 0.20 = 15 Ω. Total resistance = 30 Ω.
Activity — Measuring series circuits
Apparatus and materials
- Battery pack or low-voltage power supply (6 V max).
- Resistors (two or three known values).
- Ammeter, voltmeter (or multimeters).
- Connecting wires, switch.
- Worksheet with blank tables for current and voltage measurements.
Procedure (30-minute working window)
- Build a series circuit with one resistor. Measure current and voltage.
- Add a second resistor in series. Record current (should stay the same) and voltages across each resistor (should add up to supply voltage).
- Add a third resistor if time allows. Repeat measurements.
- Calculate Rtotal using formula and compare with measured values (V/I).
- Summarise: How is voltage shared in series circuits? How does total resistance change?
Safety
- Keep supply ≤6 V to avoid overheating resistors.
- Check connections are secure before switching on.
Discussion prompts
- How does adding more resistors in series affect total resistance?
- What happens to current when resistance increases?
- Why is voltage shared between resistors in series?
Summary
- Current is the same everywhere in a series circuit.
- Voltage is shared across components; total equals supply voltage.
- Total resistance is the sum of all resistances in series.
Check your understanding
1) Two 10 Ω resistors are connected in series to a 12 V battery. What is Rtotal?
2) What current flows in the circuit?
3) What voltage is across each resistor?
Teacher guidance
- Timing (40 min): 5 settle/recap → 10 orient with rules + demo → 30 student measurements → 5 clear/wrap-up.
- Setup: Prepare sets of resistors labelled with values. Provide worksheets with circuit diagrams and tables.
- Focus: Stress the difference between current (same everywhere) and voltage (shared).
- Differentiation: Advanced groups predict values before measuring. Struggling groups just record and describe trends.
- Exit ticket: “In a series circuit, how does total resistance change when another resistor is added?”
- Next lesson: Investigate parallel circuits and compare with series behaviour.
PS3.4 — Parallel circuits
Last lesson you investigated series circuits, measuring how current and voltage behave when resistors are connected in line. Today you will build and analyse parallel circuits, where components are connected across branches. You’ll see how current splits and how voltage behaves in parallel.
Objectives
- Describe current and voltage in parallel circuits.
- Use the formula 1/Rtotal = 1/R1 + 1/R2 + ….
- Measure current in each branch and voltage across each component.
- Compare results with series circuits.
Key Ideas & Example
Current in parallel: Splits between branches; total current = sum of branch currents.
Voltage in parallel: Same across all branches.
Resistance in parallel: 1/Rtotal = 1/R1 + 1/R2.
Example: Two 20 Ω resistors in parallel. 1/Rtotal = 1/20 + 1/20 = 2/20 → Rtotal = 10 Ω. A 10 V supply produces I = 10 ÷ 10 = 1.0 A total, split equally 0.50 A in each branch.
Activity — Measuring parallel circuits
Apparatus and materials
- Battery pack or low-voltage power supply (6 V max).
- Two or three resistors of equal value.
- Ammeter, voltmeter (or multimeters).
- Connecting wires, switch.
- Worksheet with blank tables for branch currents and voltages.
Procedure (30-minute working window)
- Build a parallel circuit with two resistors in separate branches.
- Measure current through each branch and total current from supply.
- Measure voltage across each resistor — should be the same as supply voltage.
- Add a third resistor in parallel if time allows. Repeat measurements.
- Calculate total resistance using formula. Compare with measured R = V/I.
Safety
- Keep supply ≤6 V to avoid overheating.
- Check wires are firmly connected; avoid short circuits.
Discussion prompts
- How does adding more branches in parallel affect total resistance?
- Why is voltage the same across each parallel branch?
- What happens to total current when more branches are added?
Summary
- Current splits between parallel branches; total current = sum of branch currents.
- Voltage across each branch is equal to the supply voltage.
- Total resistance in parallel is less than the resistance of any single branch.
Check your understanding
1) Two 10 Ω resistors are connected in parallel to a 12 V supply. What is Rtotal?
2) What current flows in the circuit?
3) How does this compare with two resistors in series?
Teacher guidance
- Timing (40 min): 5 settle/recap → 10 orient with parallel rules → 30 student measurements → 5 clear/wrap-up.
- Setup: Prepare resistors of equal value for easy comparison. Provide worksheets with tables and diagrams.
- Focus: Students must see that current splits but voltage stays constant. Emphasise contrast with series circuits.
- Differentiation: Advanced groups calculate efficiency or predict current splits before measuring. Struggling groups only record and describe.
- Exit ticket: “What happens to total resistance when more resistors are added in parallel?”
- Next lesson: Compare series and parallel circuits directly with prediction tasks and review game.
PS3.5 — Comparing series and parallel circuits
Last lesson you investigated parallel circuits and saw how current splits and voltage stays the same across branches. Today you will directly compare series and parallel circuits, predict how they behave, and consolidate the key differences through calculation and review tasks.
Objectives
- Predict and explain current and voltage behaviour in series vs. parallel circuits.
- Use the correct formulae for total resistance in series and parallel.
- Apply V = IR to solve problems for different circuit arrangements.
- Consolidate understanding through review questions or a quiz game.
Key Ideas & Example
Series: Current same everywhere; voltage shared; Rtotal = R1 + R2 …
Parallel: Current splits; voltage same across each branch; 1/Rtotal = 1/R1 + 1/R2 …
Example: Two 10 Ω resistors and a 20 Ω resistor.
- Series: Rtotal = 10 + 10 + 20 = 40 Ω.
- Parallel (two 10 Ω together): 1/R = 1/10 + 1/10 = 1/5 → R = 5 Ω. With 20 Ω in parallel: 1/R = 1/5 + 1/20 = 0.25 → R = 4 Ω.
Activity — Predictions, calculations, and quiz
Apparatus and materials
- Worksheet with mixed circuit diagrams (series, parallel, combination).
- Optional: resistors, meters, wires for a quick confirmatory build.
- Whiteboards or quiz game (Kahoot or team competition).
Procedure (30-minute working window)
- In pairs, predict current and voltage behaviour for circuits on worksheet.
- Calculate total resistance and currents/voltages using V = IR.
- Check predictions against calculations or quick demo circuits.
- End with short quiz/review game to consolidate series vs. parallel rules.
Safety
- Low-voltage circuits only (≤6 V).
- Switch off when not in use.
Discussion prompts
- Which arrangement (series or parallel) gives higher total resistance?
- Why is parallel wiring used in houses instead of series?
- How can you tell from a graph or calculation whether energy is shared or equal across components?
Summary
- Series circuits: current constant, voltage shared, resistance adds.
- Parallel circuits: current splits, voltage constant, resistance decreases.
- V = IR applies to both types when correct total resistance is used.
Check your understanding
1) Two 6 Ω resistors in series are connected to 12 V. What is Rtotal and the current?
2) Two 6 Ω resistors in parallel are connected to 12 V. What is Rtotal and the current?
3) Why would a string of Christmas tree lights wired in series be impractical?
Teacher guidance
- Timing (40 min): 5 settle/recap → 10 prediction & worksheet tasks → 15 calculations → 10 quiz/review → 5 wrap-up.
- Setup: Prepare worksheets with series/parallel diagrams. Have simple demo circuits ready if needed.
- Focus: Reinforce contrast between series and parallel; ensure all students can apply formulas correctly.
- Differentiation: Strong groups can handle mixed circuits; struggling groups focus only on pure series or pure parallel.
- Exit ticket: “State one key difference between series and parallel circuits.”
- Next lesson: Introduce resistivity and how material, length, and cross-section affect resistance.
PS3.6 — Resistivity
Last lesson you compared series and parallel circuits and consolidated the rules for current, voltage, and resistance. Today you will investigate what determines the resistance of a wire, introducing the concept of resistivity and testing how resistance depends on length and cross-sectional area.
Objectives
- State and use the formula R = ρL/A.
- Describe how resistance depends on length and thickness of a conductor.
- Measure and record resistance for wires of different lengths and cross-sections.
- Interpret results to estimate resistivity.
Key Ideas & Example
Resistivity (ρ): A material constant (Ω·m) that shows how strongly a material resists current flow.
Formula: R = ρL/A, where L = length of conductor, A = cross-sectional area.
Example: A copper wire (ρ ≈ 1.7 × 10-8 Ω·m), length 2.0 m, cross-sectional area 1.0 × 10-6 m². R = (1.7 × 10-8 × 2.0) ÷ (1.0 × 10-6) = 0.034 Ω.
Activity — Investigating resistivity with wires
Apparatus and materials
- Constantan or nichrome wire mounted on metre ruler.
- Battery pack or low-voltage supply (≤6 V).
- Ammeter, voltmeter (or multimeter).
- Crocodile clips, connecting wires.
- Micrometer screw gauge or caliper to measure wire diameter.
- Worksheet for recording data.
Procedure (30-minute working window)
- Measure wire diameter and calculate cross-sectional area A = πr².
- Connect circuit to measure resistance for different wire lengths (e.g., 20 cm, 40 cm, 60 cm, 80 cm).
- For each length, record V and I, calculate R = V/I.
- Plot R against L. Gradient = ρ/A, so resistivity can be estimated.
- Optional: Compare wires of different thicknesses; check how cross-sectional area affects resistance.
Safety
- Do not leave current flowing for long periods — wire may heat.
- Use low voltages only to avoid burns or damaging wire.
Discussion prompts
- Why does resistance increase with wire length?
- Why does resistance decrease when the wire is thicker?
- How can your experiment be used to estimate the resistivity of a material?
Summary
- Resistance depends on length (longer = more resistance) and cross-sectional area (thicker = less resistance).
- Resistivity is a material property: R = ρL/A.
- Graphs of R vs L allow experimental determination of ρ.
Check your understanding
1) Write the equation linking resistance, resistivity, length, and cross-sectional area.
2) Why does doubling the length of a wire double its resistance?
3) A 1.0 m wire of area 2.0 × 10-6 m² has resistance 1.5 Ω. Calculate the resistivity.
Teacher guidance
- Timing (40 min): 5 settle/recap → 10 orient + setup → 30 student measurements + graph → 5 clear.
- Setup: Mount wires on metre rulers in advance; have multimeters calibrated.
- Focus: Students must connect meters correctly and record accurate measurements of V and I.
- Differentiation: Strong groups calculate resistivity from gradient; struggling groups only describe trends.
- Exit ticket: “Which two factors affect the resistance of a wire?”
- Next lesson: Introduce potential dividers and how they split voltage in circuits.
PS3.7 — Introduction to potential dividers
Last lesson you investigated resistivity and saw how length and cross-sectional area affect resistance. Today you will learn how resistors can be combined in series to form a potential divider, which splits voltage between components. This principle is the basis of many sensing circuits.
Objectives
- Explain how potential dividers split voltage in series circuits.
- Use the formula Vout = Vin × (R2 / (R1 + R2)).
- Calculate output voltages for different resistor pairs.
- Build and test simple potential divider circuits.
Key Ideas & Example
Potential divider: Two resistors in series share the supply voltage.
Formula: Vout = Vin × (R2 / (R1 + R2)), where Vout is the voltage across R2.
Example: R1 = 4 kΩ, R2 = 6 kΩ, Vin = 12 V. Vout = 12 × (6 ÷ (4 + 6)) = 7.2 V.
Activity — Building and analysing potential dividers
Apparatus and materials
- Battery pack or DC supply (6–12 V).
- Pairs of resistors with known values.
- Voltmeter or multimeter.
- Wires, breadboard or crocodile clips.
- Worksheet with calculation tasks.
Procedure (30-minute working window)
- Build a series circuit with two resistors (R1 and R2).
- Measure total supply voltage (Vin) and output voltage across R2 (Vout).
- Calculate Vout using formula and compare with measured value.
- Repeat with different resistor pairs (swap R1 and R2 to see effect).
- Record results in table, noting % difference between measured and calculated values.
Safety
- Keep supply voltage ≤12 V.
- Ensure resistors are not overloaded — check they do not overheat.
Discussion prompts
- What determines the output voltage in a potential divider?
- How does swapping R1 and R2 affect Vout?
- Why are potential dividers important in sensing circuits?
Summary
- A potential divider splits supply voltage between resistors in series.
- Vout depends on resistor ratio: Vout = Vin × (R2 / (R1 + R2)).
- Measured values should match calculations if resistors are accurate.
Check your understanding
1) A 12 V supply is connected across R1 = 8 kΩ and R2 = 4 kΩ in series. What is Vout across R2?
2) If R1 = R2, what fraction of the supply voltage does each resistor get?
3) Why can potential dividers be used as voltage sensors?
Teacher guidance
- Timing (40 min): 5 settle/recap → 10 orient with explanation → 30 build/test/calculations → 5 clear.
- Setup: Provide labelled resistor pairs, voltmeters, and worksheets with calculation tasks.
- Focus: Students must understand resistor ratio determines output voltage, not just resistor size individually.
- Differentiation: Strong groups derive formula for Vout. Struggling groups focus on measuring and comparing with predictions.
- Exit ticket: “If R2 increases, what happens to Vout?”
- Next lesson: Apply potential dividers to sensing circuits using LDRs and thermistors.
PS3.8 — Sensing circuits (LDRs and thermistors)
Last lesson you learned how potential dividers split voltage depending on resistor ratios. Today you will apply this to sensing circuits, using components like LDRs (light-dependent resistors) and thermistors, which change resistance with light and temperature. These allow circuits to act as automatic sensors.
Objectives
- Describe how LDRs and thermistors change resistance with light or temperature.
- Build potential divider circuits using sensors as one resistor.
- Measure how Vout changes with light intensity or temperature.
- Explain applications of sensing circuits in real life.
Key Ideas & Example
LDR: Resistance decreases as light intensity increases.
Thermistor (NTC type): Resistance decreases as temperature increases.
Application: In a potential divider, the sensor replaces R1 or R2. As its resistance changes, Vout varies, creating a signal for light/heat levels.
Example: A 5 V supply with LDR and 10 kΩ resistor in series. In bright light, LDR = 2 kΩ → Vout = 5 × (10 ÷ (2 + 10)) = 4.2 V. In dark, LDR = 20 kΩ → Vout = 5 × (10 ÷ (20 + 10)) = 1.7 V.
Activity — Building sensing circuits
Apparatus and materials
- Battery pack or DC supply (5 V).
- LDRs, thermistors, fixed resistors.
- Voltmeter or multimeter.
- Heat source (e.g., lamp, warm hand, beaker of warm water).
- Light source (torch, covering materials).
- Breadboards and wires.
Procedure (30-minute working window)
- Build a potential divider with an LDR and fixed resistor.
- Measure Vout across the fixed resistor in bright light and in shadow. Record values.
- Repeat using a thermistor. Measure Vout at room temperature and after gentle warming.
- Record results in a table. Sketch how Vout changes with light or temperature.
- Extension: Connect to LED/transistor circuit to see automatic switching in action.
Safety
- Use low-voltage supply only (≤5 V).
- Handle heat sources carefully — do not overheat thermistor.
- Switch off when circuits are not in use.
Discussion prompts
- Why does an LDR’s resistance decrease as light increases?
- How can a thermistor-based circuit act as a thermostat?
- What are the advantages of using potential divider circuits for sensors?
Summary
- LDRs respond to light, thermistors respond to temperature.
- In potential dividers, these components change Vout as their resistance varies.
- Sensing circuits form the basis of many automatic devices (e.g., street lights, thermostats).
Check your understanding
1) What happens to an LDR’s resistance as light intensity increases?
2) In a thermistor circuit, what happens to resistance as temperature increases?
3) Give one real-life application of each sensor.
Teacher guidance
- Timing (40 min): 5 settle/recap → 10 orient + setup → 30 build/test with LDR and thermistor → 5 clear.
- Setup: Provide labelled sensors and fixed resistors. Prepare lamps or torches and simple heat sources.
- Focus: Students must see that Vout depends on sensor resistance. Link this to control circuits (inputs for switching).
- Differentiation: Strong groups design LED driver circuits. Struggling groups focus on measuring and describing Vout changes.
- Exit ticket: “In one sentence, explain how an LDR circuit can switch a light on automatically at night.”
- Next lesson: Apply all knowledge in a mini-project: design and present a sensor circuit.
PS3.9 — Mini-project: design a sensor circuit
Last lesson you experimented with LDRs and thermistors in potential divider circuits. Today you will apply your knowledge in a mini-project: designing, building, and testing a sensor circuit that responds to light or temperature. This project pulls together ideas of resistance, potential dividers, and sensing applications.
Objectives
- Design and build a working sensor circuit using an LDR or thermistor.
- Explain how the circuit functions using resistance and potential divider concepts.
- Test circuit performance and collect data on Vout behaviour.
- Prepare a short presentation or poster explaining design and application.
Key Ideas & Example
Design stage: Choose input sensor (LDR for light, thermistor for temperature). Use a fixed resistor to form a potential divider. Connect an LED, buzzer, or meter as an output indicator.
Example application: Street-light circuit: LDR + resistor form divider. In dark, LDR resistance is high → Vout rises → LED switches on via transistor.
Activity — Building a sensor circuit project
Apparatus and materials
- LDRs or thermistors.
- Fixed resistors, transistors, LEDs/buzzers.
- Battery pack (≤6 V) or low-voltage supply.
- Breadboards and connecting wires.
- Worksheet or lab booklet for circuit diagram and notes.
Procedure (30-minute working window)
- In groups, choose to design a light sensor or temperature sensor circuit.
- Sketch the circuit diagram with correct symbols.
- Build circuit on breadboard. Adjust resistor values for reliable switching.
- Test by varying light level (torch/shadow) or temperature (warm hand/water). Record Vout readings.
- Document design choices: why this resistor arrangement, how the output works.
Safety
- Low-voltage circuits only (≤6 V).
- Do not overheat thermistors with strong heat sources.
- LEDs/buzzers should be connected with correct polarity and limiting resistors.
Discussion prompts
- Why does your circuit respond differently under different light/temperature conditions?
- What factors determined your choice of fixed resistor value?
- How could your circuit be improved to be more reliable in real life?
Summary
- A potential divider with an LDR or thermistor can act as a simple sensing circuit.
- Testing shows how Vout varies with light or temperature.
- Documenting design choices is key to explaining the physics behind the circuit.
Check your understanding
1) What happens to Vout in a light-sensing circuit when it gets darker?
2) Why is a fixed resistor always used with an LDR/thermistor in a potential divider?
3) Suggest one real-world use of your sensor circuit design.
Teacher guidance
- Timing (40 min): 5 settle/intro → 10 design stage → 20 build/test → 5 documentation/wrap-up.
- Setup: Provide trays with sensors, resistors, LEDs, breadboards, and spare wires. Have example diagram ready on board.
- Focus: Encourage clear link between physics (resistance change → Vout change) and circuit function.
- Differentiation: Advanced groups add transistor stage to drive outputs; struggling groups focus on measuring Vout change.
- Exit ticket: “What is the role of the sensor in your potential divider circuit?”
- Next lesson: Review and assessment of the whole unit.
PS3.10 — Review and assessment
Last lesson you designed and tested a sensor circuit using an LDR or thermistor. Today you will consolidate everything from this unit: reviewing the behaviour of series and parallel circuits, Ohm’s Law, resistivity, and potential dividers, and completing a short quiz to check your understanding.
Objectives
- Review current, voltage, and resistance in series and parallel circuits.
- Recall and apply Ohm’s Law, resistivity, and potential divider equations.
- Demonstrate understanding in a written quiz and reflection activity.
- Summarise applications of circuits in real-world devices.
Key Ideas
V = IR Ohm’s Law.
R = ρL/A Resistivity equation.
Vout = Vin × (R2 / (R1 + R2)) Potential divider.
Series: Current same, voltage shared, R adds.
Parallel: Voltage same, current splits, R decreases.
Activity — Quiz and reflection
Apparatus and materials
- Quiz sheet (10–12 mixed questions: calculations + concepts).
- Formula sheet for reference.
- Reflection worksheet (“What I understand well, what I need to revise”).
- Optional: interactive quiz platform (e.g., Kahoot).
Procedure (30-minute working window)
- Begin with 5 quick-fire recap questions on whiteboards (class warm-up).
- Complete written quiz individually (~15 minutes).
- Self-mark or peer-mark with class discussion of solutions.
- Students fill in reflection worksheet: one secure idea + one target for improvement.
Safety
- No safety issues — classroom written activity.
Discussion prompts
- Which circuit type (series or parallel) is used in homes? Why?
- What is the purpose of potential divider circuits in sensors?
- How can resistivity investigations be applied in technology?
Summary
- You can now describe current, voltage, and resistance in series and parallel circuits.
- You can apply V = IR, R = ρL/A, and the potential divider equation.
- You have seen how circuits are used in sensing and practical applications.
Check your understanding
1) State the equation for Ohm’s Law and define each symbol.
2) How does doubling wire length affect resistance?
3) Explain briefly how an LDR potential divider can act as a night sensor.
Teacher guidance
- Timing (40 min): 5 settle → 10 warm-up review → 15 written quiz → 10 feedback/discussion → 5 reflection/closure.
- Setup: Prepare printed quizzes and reflection sheets. Have formula sheet visible on board.
- Focus: Ensure students can recall equations and apply them to both calculations and applications.
- Differentiation: Advanced learners solve multi-step resistor problems. Struggling learners focus on qualitative differences between series and parallel.
- Exit ticket: “One formula I can use confidently, and one I need more practice with.”
- Closure: Connect back to real-world circuits: sensors, electronics, and household wiring.
Now test yourself
Click on the button below to access the self-tests for MYP9 and MYP10.
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