The production possibility frontier (every paper, Question Three)

A PPF shows the trade-off between two types of goods. A point INSIDE the curve is inefficient; the curve itself SHIFTING shows a change in the economy's potential capacity.

Reading the graph

A MOVEMENT ALONG the curve (e.g. from point A to point B) shows re-allocating existing resources — more of one good, less of the other. The amount given up is the opportunity cost.
The curve SHIFTING outward shows growth — more of BOTH goods becomes possible, from more/better resources.
The curve shifting outward MORE in one direction than another shows biased growth — capacity has grown more for one type of good.
A future PPF built from more capital/infrastructure spending (moving toward capital goods) shifts out FURTHER than one built from more consumer spending, because capital goods raise future productive capacity directly.

Exam-style The government raises taxes to fund infrastructure spending (point A → point B) Explain the opportunity cost, and why the resulting future PPF differs from one built by staying at point A. Moving from A to B (more infrastructure/capital goods) means giving up some consumer goods NOW — that lost consumer-goods output is the opportunity cost, labelled as the vertical/horizontal gap between A and B. Because point B invests in capital/infrastructure goods, the ECONOMY'S FUTURE productive capacity rises more than if resources had stayed at point A producing consumer goods. So the future PPF built from point B (X*) sits further outward than the future PPF built from point A (Y*) — capital spending compounds into more capacity later, consumer spending does not. ✓ Investing in capital/infrastructure goods now costs consumer goods now, but buys a BIGGER future PPF — the core trade-off this model tests.

PPF feature	What it shows
Point inside the curve	Inefficient — resources not fully/well used
Movement along the curve	Reallocating existing resources (opportunity cost)
Curve shifting outward	Growth — more of BOTH goods possible

Practice for this standard covers the whole topic — flashcards and quiz.