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ohm's law & resistor networks

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4 detailed 50-minute lessons with teaching scripts, worked examples, parent guides, and assessment criteria.

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Lesson Overview

Total Lessons: 4
Tier: Foundation and Higher
Duration: 50 minutes per lesson (200 minutes total)
Exam Boards: AQA, Edexcel, OCR, Eduqas, CCEA

Learning Objectives

Prerequisites

Materials & Equipment

Lesson 1: Introduction: ohm's law & resistor networks

Duration: 50 minutes

Starter Activity (5 minutes)

Quick Recall

Write down everything you already know about ohm's law & resistor networks. Then check against the key terms: key terms from ohm's law & resistor networks. Use a mini-whiteboard or paper.

Main Content (35 minutes)

Parent/Teacher Guide:
Before lesson: Read the script below. Pre-teach key vocab: key terms from ohm's law & resistor networks.
If stuck: Re-read the revision notes (link above), then break the content into smaller steps.
Extension: See the Stretch & Challenge ideas in Lesson 4.
Teaching Script (35 mins):
Mins 0-5 - Hook: "Today: ohm's law & resistor networks. By the end you will be able to answer exam questions on it unaided. It connects to the rest of Electronics because the ideas here recur across the spec."
Mins 5-20 - Direct Instruction: Work through the core ideas below one at a time; after each, ask your student to explain it back in their own words.
Mins 20-30 - Guided Practice: Model the worked example together, then let your student attempt the first practice question with guidance.
Mins 30-35 - Independent Practice: 2-3 practice questions from Lesson 3 below, with immediate feedback.
First Look

Start with the revision notes summary, then attempt: explain the key ideas of ohm's law & resistor networks

Plenary (5 minutes)

Check Out

Your student states one thing they learned and one question they still have about ohm's law & resistor networks.

Lesson 2: Core Concepts: ohm's law & resistor networks

Duration: 50 minutes

Starter Activity (5 minutes)

Review Previous Lesson

Quick recap: write 3 key points from Lesson 1 on ohm's law & resistor networks. Check them against the notes below.

Main Content (35 minutes)

Key Fact: In series, total resistance R_total = R1 + R2 + R3; the same current flows through each resistor.
Key Fact: In parallel, 1/R_total = 1/R1 + 1/R2 + 1/R3; the same voltage is across each resistor.
Key Fact: For two resistors in parallel: R_total = (R1 × R2)/(R1 + R2).
Key Fact: A potential divider uses two series resistors to produce a fraction of the supply voltage: V_out = V_in × R2/(R1 + R2).
Key Fact: In series circuits, voltage splits proportionally to resistance: the larger resistor gets the larger voltage share.
Key Fact: In parallel circuits, each branch carries current inversely proportional to its resistance.

Practice (10 minutes)

Q: explain the key ideas of ohm's law & resistor networks

Answer:

Plenary (5 minutes)

Explain Back

Your student teaches the key points back to you without looking. Fill any gaps immediately.

Lesson 3: Application: ohm's law & resistor networks

Duration: 50 minutes

Starter Activity (5 minutes)

Quick Recall

Recall the key terms: key terms from ohm's law & resistor networks. Define each in one sentence.

Main Content (35 minutes)

Parent/Teacher Guide: Let your student attempt each question alone first, then compare with the model answer. Award method marks for correct working even if the final answer is wrong.

Work through the practice questions on the revision notes page for this topic.

Plenary (5 minutes)

Error Review

Review any questions answered incorrectly. Identify whether the error was knowledge, method, or reading the question.

Lesson 4: Exam Practice: ohm's law & resistor networks

Duration: 50 minutes

Starter Activity (5 minutes)

Command Words

Review what these command words require: state (one point), describe (say what happens), explain (say why), compare (both sides), evaluate (judgement).

Main Content (35 minutes)

Extended Answer

Extended question: Full-Mark Response Explain how to calculate the total resistance of a mixed series-parallel resistor network, and describe how a potential divider works. <div class="

To calculate total resistance of a mixed network, first identify which resistors are in parallel and combine them using 1/R_total = 1/R1 + 1/R2 + …, then add any series resistances to get the overall equivalent resistance. A potential divider consists of two resistors (R1 and R2) in series across a supply voltage. The output voltage taken across R2 is V_out = V_in × R2/(R1 + R2). The voltage divides in proportion to the resistances: the larger R2 is relative to R1, the greater the output voltage. If a load is connected across R2, it forms a parallel combination with R2, reducing the effective lower resistance and therefore reducing V_out. This loading effect must be considered in practical circuits.

Exam Tips: Always draw the circuit and label it before attempting calculations. | For mixed networks, simplify parallel sections first, then add series resistances. | State the formula for a potential divider before substituting values. | Show that the sum of voltages across series resistors equals the supply voltage as a check. | Remember that a loaded potential divider will have a lower output than the unloaded calculation predicts.
Common Errors: ✗ Adding resistances directly for a parallel combination. ✓ Use 1/R_total = 1/R1 + 1/R2 for parallel; add directly only for series. ✗ Using R_total = R1 + R2 when resistors are in parallel. ✓ For two parallel resistors, use R_total = (R1 × R2)/(R1 + R2). ✗ Forgetting to account for loading when a potential divider drives another circuit. ✓ Recalculate the lower branch as R2 in parallel with the load resistance. ✗ Assuming current splits equally in parallel branches. ✓ Current splits inversely proportional to branch resistance.
Stretch & Challenge (Grade 8-9):
  • Synoptic links: explain how ohm&#x27;s law &amp; resistor networks connects to another Electronics topic you have studied
  • Real-world: research one real-world use or example of ohm&#x27;s law &amp; resistor networks
  • Critical: "What are the limitations of the models used in ohm&#x27;s law &amp; resistor networks?"

Plenary (5 minutes)

Assessment Criteria
  • Got it: Confident explanation + correct worked examples
  • Getting there: Main points OK, needs support with detail
  • Not yet: Confused on key concepts - re-run Lesson 2

Homework & Consolidation

Recommended Resources

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