The Feynman technique: explain, check, then apply

Choose this question: Why is the current the same before and after a lamp in a simple series circuit? Imagine one battery, one lamp and connecting wires forming a single closed loop. Consider steady operation, not the instant of switching on.

Here is an intentionally flawed first explanation: “The battery sends current to the lamp. The lamp uses some current to make light, so less current returns to the battery.”

This is an original teaching example, not a student quotation or an examiner-marked answer. Before reading on, underline the part you think is wrong and write what it predicts an ammeter would show after the lamp. It predicts a smaller reading. That prediction makes the mistake testable.

The problem is “uses some current”, not the length or difficulty of the words. This explanation treats current as a fuel which gets consumed. It confuses the flow of electric charge with the transfer of energy. Replacing “current” with “electricity” would make the sentence less precise, not more correct.

Current is the rate of flow of charge, measured in amperes (A). In steady operation, charge is not continually piling up in the lamp or disappearing inside it. The rate entering must match the rate leaving. That is why the ammeter readings are equal around this single loop.

Ask two different questions: “How much charge passes each second?” and “Where is energy transferred?” Keeping them separate is the correction you need.

AQA’s GCSE Physics electricity specification defines current as a rate of charge flow and states that current is the same through components in series. The OpenStax explanation of series circuits helps separate current from energy transfer.

A corrected explanation is: “In this steady series circuit, the same amount of charge passes each point each second, so the current is the same before and after the lamp. The lamp does not consume charge. Energy is transferred from the battery’s chemical store to the lamp and its surroundings; the lamp emits light and heats its surroundings.”

Close the source and reconstruct that explanation. Keep charge, current, energy transfer and series circuit: they do different jobs. If you say only “the same electricity goes round”, ask yourself which quantity you mean. Avoid imagining electrons as delivery trucks which return empty of energy.

The curriculum reference here is AQA GCSE Physics 8463 in England. OpenStax is a US physics textbook, used here for the underlying science rather than UK assessment requirements. Use your own course specification for assessment requirements.

Now leave the lamp example behind. On paper, connect a 6 V ideal supply and two fixed resistors, 10 Ω and 20 Ω, in one series loop. Assume constant resistances and negligible wire and ammeter resistance.

Try before checking: What current would an ammeter read before the first resistor, between the resistors and after the second? If the 20 Ω resistor is replaced by a 50 Ω resistor, which readings change? Explain why the second resistor does not “use up” more current.

You need two rules: series resistances add, and I = V ÷ R, where I is current in A, V is the supply potential difference in volts, and R is the total resistance in ohms (Ω). These rules are included in the AQA electricity specification. Write both the numbers and the explanation before continuing.

Initially, total resistance is 10 + 20 = 30 Ω, so I = 6 ÷ 30 = 0.20 A. All three positions read 0.20 A.

After replacement, total resistance is 10 + 50 = 60 Ω, so I = 6 ÷ 60 = 0.10 A. All three positions now read 0.10 A. The greater total resistance reduces the rate of charge flow throughout the loop at the same supply potential difference. It does not remove current as charge passes through the second resistor.

What your answer tells you: Different readings at different positions mean the current-consumption idea remains. Equal readings of 0.20 A after the replacement mean you kept the series-current rule but missed the effect of total resistance. Correct numbers without a reason are a cue to explain the mechanism again. These calculations are an illustrative exercise, not a past-paper question.

Choose one relationship you need to understand, rather than trying to explain an entire subject. Keep the first attempt: it gives you something specific to repair.

Self-explanation means generating connections and reasons, rather than only repeating information. A 2018 meta-analysis by Bisra and colleagues found positive average learning effects from prompting self-explanation across the studies it examined. That is evidence about a related learning process, not proof that a particular branded Feynman routine is best for GCSE revision.

Treat the sequence here as practical guidance, not a guaranteed route to mastery or higher grades. Explaining confidently can still mean explaining an error confidently. One successful application is useful evidence about that question, not proof that you know the whole topic.

Use explanation when you need to uncover a causal misunderstanding. Use retrieval practice when you need to check what you remember, and practise the actual assessed task when you need to write an essay, solve a calculation or work under exam conditions. For the broader routine, read active recall and spaced repetition or how to revise effectively.