nst current $I$ on the horizontal axis.\n\nExplain how this graph can show that the wire obeys Ohm's law.","markscheme":"- **(i)** States that the graph is a straight line passing through the origin (0,0) M1\n- **(i)** Explains that this shows the potential difference is directly proportional to the current (constant resistance) A1","marks":2,"order":0,"markingRubric":null,"explanation":{"methods":[{"id":"read_v_i_graph","label":"Read the V-I graph","steps":[{"type":"graph","order":1,"title":"Recognise the required line","viewport":{"top":11,"left":-0.2,"right":5.2,"bottom":-0.5},"axisLabels":{"x":"Current, I / A","y":"Potential difference, V / V"},"description":"A wire obeys Ohm's law when the $V$-$I$ graph is a straight line through the origin. This earns M1.","expressions":[{"id":"expr-0","latex":"y=2x\\left\\{0\\le x\\le5\\right\\}"},{"id":"expr-1","color":"red","latex":"(0,0)","pointStyle":"point"}]},{"type":"text","order":3,"title":"Explain the relationship","content":"A straight line through the origin shows that potential difference is directly proportional to current.\n\nFor any non-zero current, the ratio $\\frac{V}{I}$ is constant. This ratio is the resistance, so the wire has constant resistance and obeys Ohm's law. **This earns A1.**","highlights":[{"text":"Explain how this graph can show that the wire obeys Ohm's law.","location":"specification"}]}]}],"generatedAt":"2026-07-21T18:08:39.831Z","modelVersion":"gpt-5.6-terra+diagrams-1","explanationVersion":"v3"},"options":[]},{"id":"379582e7-1cfe-4c4c-9fac-6db9f2f15bac","label":"b","content":"At the highest current reading of $2.5\\text{ A}$, the plotted potential difference lies slightly above the expected straight line of best-fit. Suggest a physical reason for this observation.","markscheme":"- **(ii)** Identifies that high currents cause a significant heating effect, increasing the temperature of the wire M1\n- **(ii)** Explains that this temperature rise increases the resistance of the wire, requiring a higher potential difference for the same current A1","marks":2,"order":1,"markingRubric":null,"explanation":{"methods":[{"id":"heating_effect","label":"Heating effect explanation","steps":[{"type":"text","order":2,"title":"Identify the heating effect","content":"At the highest current, the heating effect is significant, so the wire’s temperature increases. **This earns M1.**","highlights":[{"text":"At the highest current reading of $2.5\\text{ A}$","location":"specification"}]},{"type":"text","order":3,"title":"Link resistance to voltage","content":"For a metal alloy wire, a higher temperature means a higher resistance. Therefore, at the same current of $2.5\\text{ A}$, a larger potential difference is needed. The plotted point is therefore above the original straight-line trend. This explanation earns **A1**.","highlights":[{"text":"the plotted potential difference lies slightly above the expected straight line of best-fit","location":"specification"}]}]}],"generatedAt":"2026-07-21T18:12:38.100Z","modelVersion":"gpt-5.6-terra+diagrams-1","explanationVersion":"v3"},"options":[]},{"id":"c2a715b6-d78c-4496-949d-8f0bdee082c3","label":"c","content":"State two ways the technician can check if their experimental results are reproducible.","markscheme":"- Suggests having a different investigator/technician perform the experiment B1\n- Suggests repeating the experiment using different apparatus, instruments, or in a different environment B1","marks":2,"order":2,"markingRubric":null,"explanation":{"methods":[{"id":"checking_reproducibility","label":"Checking reproducibility","steps":[{"type":"text","order":0,"title":"Define reproducibility","content":"Reproducibility means obtaining similar results when the experiment is carried out independently, for example by a different person or using different equipment or in a different environment."},{"type":"text","order":1,"title":"Change the investigator","content":"Ask a **different technician** to perform the experiment independ

Simple circuits

Question 21

Simple circuits Questions

Simple circuits

Question 21

Simple circuits Questions