Ohm's Law
Ohm's Law states that the current through a conductor is directly proportional to the potential difference across it, provided the temperature and other physical conditions remain unchanged. This relationship is expressed by the equation V = IR, where V is voltage, I is current, and R is resistance.
Full topic guide: the detailed syllabus page with worked examples and common mistakes lives at studyvector.co.uk/gcse/physics/electricity/ohms-law.
Topic preview: Ohm's Law
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Coverage and provenance
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Topic explanation
Ohm's Law states that the current through a conductor is directly proportional to the potential difference across it, provided the temperature and other physical conditions remain unchanged. This relationship is expressed by the equation V = IR, where V is voltage, I is current, and R is resistance.
Ohm's Law is easiest to revise when it is treated as a precise exam behaviour, not a loose note-taking category. In GCSE Physics, the goal is to recognise how the topic appears in a question, identify the command word, and decide what evidence, method, or vocabulary earns marks. StudyVector keeps this page tied to AQA · Edexcel · OCR language where coverage is available, then routes practice towards the same topic so revision moves from explanation into retrieval.
A strong revision session starts with a short recall check. Write down the rule, definition, process, or method linked to Ohm's Law before looking at any notes. Then answer one exam-style prompt and compare your answer with the mark-scheme logic: did you make a clear point, support it with the right step, and avoid drifting into a nearby topic? This matters because many lost marks come from almost-correct answers that do not match the expected structure.
Use this guide as the first layer: understand the topic, look at the worked examples, complete the mini quiz, then move into full practice. The full StudyVector practice loop is designed to capture whether mistakes are caused by knowledge, method, language, or timing. That distinction is important. If the error is factual, you need reteaching. If the error is method-based, you need a worked retry. If the error is wording, you need command-word calibration. That is how Ohm's Law becomes a controlled revision target rather than another page in a folder.
Lost marks → repair task
Why marks are usually lost here
These are the error patterns StudyVector looks for after an attempt. The goal is not a generic explanation; it is one repair move and one follow-up question.
Unit, formula, or method slip
Examiner move: Select the correct method and keep units, substitutions, signs, and rounding visible.
Repair drill: Redo the calculation or method line slowly, naming the formula before substituting values.
Missing chain of reasoning
Examiner move: Show the link between point, method, evidence, and conclusion instead of jumping to the final line.
Repair drill: Write the missing because/therefore step, then retry one isomorphic question.
Weak evidence or data reference
Examiner move: Use a precise value, quote, example, diagram feature, or syllabus term to support the claim.
Repair drill: Add one concrete reference to the answer and remove any generic sentence that does not earn a mark.
Mini quiz
Use these checks before full practice. They test topic recognition, exam technique, and whether you can connect the explanation to a marked response.
1. What should you check first when a Ohm's Law question appears in GCSE Physics?
- A.The command word and the exact topic focus
- B.The longest paragraph in your notes
- C.A memorised answer from a different topic
2. Which revision action gives the strongest evidence that Ohm's Law is improving?
- A.Rereading the explanation twice
- B.Answering a timed exam-style question and reviewing lost marks
- C.Highlighting every key phrase in the topic notes
Sample questions
Topic-specific public question previews are still being reviewed. We keep them off public pages until the topic match is safe.
Exam tips
- Read the command word carefully — "explain" needs reasons; "state" expects a short fact.
- For Ohm's Law, show structured working even when you are practising multiple choice — it builds accuracy under time pressure.
- Mark yourself against the mark scheme style: one clear point per mark, in logical order.
- Come back to this topic after a day or two; short spaced reviews beat one long cram.
Worked examples
Example 1
Modelled exam response
A resistor has a resistance of 12Ω and the potential difference across it is 6V. What is the current flowing through it? Solution: Using Ohm's Law, I = V/R. I = 6V / 12Ω = 0.5A.
Example 2
Identify the task before answering
Question type: a Ohm's Law prompt asks for a clear response in GCSE Physics. Step 1: underline the command word. Step 2: name the exact part of Ohm's Law being tested. Step 3: decide whether the mark scheme wants a definition, method, explanation, comparison, or calculation. Why it works: most weak answers fail before the content starts because they answer the topic generally rather than the exact exam task.
Example 3
Turn feedback into a repair task
Suppose your answer shows partial understanding but loses marks for precision. First, rewrite the missing mark as a short target: "I need to state the mechanism, unit, reason, or evidence explicitly." Then answer one similar question without notes. Finally, compare the second attempt with the first and check whether the same mark was recovered. Why it works: Ohm's Law improves faster when feedback creates a specific retry, not another passive reading session.
Next revision routes from this subject
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Common mistakes
- Applying Ohm's Law to non-ohmic conductors. Ohm's Law only applies to components with a constant resistance, like a resistor at a constant temperature. It does not apply to filament lamps or diodes.
- Rearranging the formula incorrectly. A common mistake is to write I = VR or R = VI.
- Forgetting the condition that physical conditions (like temperature) must be constant. The resistance of many components changes with temperature.
Exam board notes
A key law in all GCSE Physics specifications (AQA, Edexcel, OCR). Understanding which components are ohmic and non-ohmic is crucial.
FAQs
What is an ohmic conductor?
An ohmic conductor is a component that obeys Ohm's Law. Its resistance is constant, so the graph of voltage against current is a straight line through the origin.
What is the relationship between current and voltage in Ohm's Law?
Current is directly proportional to voltage. This means if you double the voltage, you double the current, as long as the resistance stays the same.
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