One curve, and it carries five ideas: It shows the most an economy can make of two goods, using everything it has.
Scarcity, choice, opportunity cost, efficiency and growth — all in one picture. That is why it comes first, and why examiners keep coming back to it.
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Where a point sits tells you everything
- On the curve — everything is used well. Efficient.
- Inside — something is idle. Unemployment or waste.
- Outside — impossible today. Not forever, just not now.
Label the axes with goods, never money: Tonnes of wheat. Units of capital. Never price.
An unlabelled axis loses the mark before the examiner reads a word.
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Why the curve slopes down: Resources are scarce. More of one good always means less of the other.
That trade-off is opportunity cost — drawn.
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Bowed out — the normal shape
- Opportunity cost increases.
- Resources are not equally good at both jobs.
- Each extra unit costs more than the last.
Straight line — the special case
- Opportunity cost is constant.
- Resources are equally good at both.
- Used in Unit 4 for comparative advantage.
Why bowed out is the realistic one: A combine harvester is brilliant at wheat and useless at laptops.
Shift towards laptops and you start moving your worst-suited resources — so each laptop costs more wheat than the last.
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A point inside the curve
Resources sitting idle — unemployed workers, empty factories.
The economy could have more of both goods.
Moving from inside onto the curve
Actual growth — using what you already have, better.
The curve does not move.
The whole curve shifting out
Growth in capacity — more resources, or better technology.
The limit itself has moved.
The curve shifting in
Capacity lost — war, disaster, skilled workers leaving.
One end stretching, the other not
Technology improved in one industry only — so the curve pivots.
The distinction that earns marks: Moving toward the curve = using what you have.
The curve moving = you have more to use.
Recovering from recession is the first. Investing in education is the second.
Every question tagged here has been a PPC question: Sketch a PPC showing better human capital. Sketch a trade-off between two sectors. Use a PPC to explain a trade deal.
The marks are on the diagram. Draw it first.
What the diagram must have
- Both axes named with the two goods — never price.
- The curve labelled PPC.
- Only the change asked for, and both before and after.
The trap — drawing a shift when it is only a move: Unemployment falls does not shift the curve. The economy moves from inside the curve towards it.
Only more resources or better technology move the curve itself.
Using a production possibilities curve diagram, explain the impact of increased investment in human capital on a country's production possibilities.
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