MCQ Answers
1. C — In series, current is the same at every point (single path).
2. A — P = V × I = 240 × 8 = 1,920 W.
3. B — Adding parallel branches reduces total resistance (more paths).
4. C — Filament resistance increases with temperature, making it non-ohmic.
5. A — Voltmeters measure potential difference and must be in parallel.
SAQ 1 — Series vs Parallel (3 marks)
Marking Criteria: 1 mark — two valid differences in voltage/current behaviour. 1 mark — series example with explanation. 1 mark — parallel example with explanation.
Model answer: In a series circuit, the current is the same at every point because there is only one path, but the voltage is shared across components. For example, old Christmas tree lights were wired in series — when one bulb burned out, the entire string went dark because the single path was broken.
In a parallel circuit, the voltage is the same across every branch because all branches connect across the same two points, but the current splits between branches. For example, the powerpoints in an Australian home are wired in parallel — you can turn off the kitchen light while your phone continues charging because each device has its own independent path to the 240 V mains supply.
SAQ 2 — Ohm's Law and Power (4 marks)
Marking Criteria: 1 mark — calculates original resistance correctly. 1 mark — predicts new current with working. 1 mark — calculates both powers correctly. 1 mark — explains inverse proportionality.
Model answer: First, calculate the original resistance using Ohm's Law:
R = V / I = 12 V / 0.6 A = 20 Ω
When the resistance is doubled to 40 Ω, the new current is:
I = V / R = 12 V / 40 Ω = 0.3 A
The current has halved because resistance doubled while voltage stayed constant. This shows the inverse proportionality between current and resistance in Ohm's Law.
Power calculations:
Original: P = V × I = 12 × 0.6 = 7.2 W
New: P = V × I = 12 × 0.3 = 3.6 W
The power has also halved, which makes sense because less current is flowing at the same voltage.
SAQ 3 — NEM Parallel Architecture (5 marks)
Marking Criteria: 1 mark — explains parallel architecture of NEM. 1 mark — describes voltage consistency in parallel. 1 mark — describes independence (one station off = others continue). 1 mark — explains series consequences (voltage addition, blackout risk). 1 mark — uses specific terminology (grid stability, AEMO, transmission).
Model answer: The National Electricity Market (NEM) uses parallel architecture because Australia's power stations must all feed into the same grid voltage (approximately 240 V at household level, stepped up to 132–500 kV for transmission). In a parallel system, every generator connects across the same grid "rails," meaning each station contributes current while maintaining the same voltage. This is essential because appliances, factories, and homes are all designed for a specific voltage.
A critical advantage of parallel connection is independence. When the Callide coal power station in Queensland went offline for maintenance in 2021, the other 200+ generators across the NEM continued supplying power. No household lost electricity because parallel branches operate independently — one path failing does not break the others.
If all power stations were connected in series, the consequences would be catastrophic. First, the voltages would add: connecting even two 20 kV generators in series would produce 40 kV, far exceeding safe transmission levels and destroying transformers. Second, any single station failure would cause a total blackout across the entire network, because series circuits have only one path. There would be no redundancy, no capacity for maintenance, and no way to integrate variable renewable sources like wind and solar.
The NEM's parallel design is therefore fundamental to grid stability, allowing AEMO to dispatch power from the cheapest available sources while maintaining constant voltage for 10 million+ Australian homes and businesses.