In simple terms
A friendly intro before the formal notes — no formulas yet.
Why You Can't Have It All
Economics starts with a simple truth: we can't have everything we want because our resources are limited. This forces us to make choices, and every choice has a hidden cost — the best thing we gave up.
Imagine you have £10 at a food market. You want both a gourmet burger (£10) and a fancy smoothie (£10), but can only afford one. Choosing the burger means giving up the smoothie. That forgone smoothie is the opportunity cost of your burger — the value of what you didn't choose.
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Scarcity forces choice — not all wants can be satisfied.
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Opportunity cost is the value of the next best alternative forgone.
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What to produce? How? For whom? — the basic economic questions.
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The PPC puts it together: points on the curve show scarcity and opportunity cost; an outward shift shows growth.
Explore the concept
Use the live diagram, PhET or GeoGebra sim, and synced steps — play it, drag controls, or tap a step.
Step-synced diagram — highlights what to look for in the simulation above.
Scarcity forces choice
Scarcity forces choice — not all wants can be satisfied.
1 more simulation for this topic — run them in the Simulations section below
Simulations
Every simulation here runs the real model — try the steps on a card, then check what you see against the notes.
1 simulation
- GeoGebraIB 1.1
PPC with constant opportunity cost
A straight-line PPC for Item X and Item Y with three labelled points: Efficiency on the line, Recession (inefficiency) inside, Not Possible (yet) beyond.
Try this
- Say why each of the three labelled points sits where it does.
- Follow the dotted guides from the Efficiency point to the axes to read one possible output mix.
- Compare the straight line with a bowed-out PPC: here each extra unit of Item X always costs the same amount of Item Y.
Look for A straight-line PPC means constant opportunity cost; a bowed-out curve means opportunity cost rises as resources are moved from one good to the other.
Craig Burt · GeoGebra · GeoGebra Terms of Service
Full topic notes
Formal explanation with the rigour you need for the exam.
The fundamental economic problem: scarcity
Scarcity is the starting point for all economic analysis. It is the conflict between human wants, which are effectively infinite, and the resources available to satisfy them, which are finite. Note that scarcity is not the same as poverty: it affects everyone, from the poorest individual to the wealthiest nation, because no one can have an infinite amount of everything.
The limited resources are the factors of production, grouped into four categories: Land (all natural resources), Labour (human effort in production), Capital (man-made aids to production such as machinery and factories), and Entrepreneurship (organising the other three factors and bearing the risk of production).
Scarcity exists because wants are unlimited but resources are finite.
Scarcity is universal — it affects all societies and individuals, not only the poor.
The scarce resources are the four factors of production: Land, Labour, Capital and Entrepreneurship.
From scarcity to choice and opportunity cost
Because of scarcity we cannot satisfy all our wants, so we must choose. When you buy a textbook you may be choosing not to buy a video game; when a government funds a hospital it may be choosing not to upgrade a motorway. Every choice involves a trade-off.
This leads to one of the most important concepts in economics: opportunity cost — the value of the next best alternative forgone. It is not only about money; it can be time, enjoyment or any benefit given up. The phrase 'next best' is essential: only the single most valuable alternative sacrificed counts, not the sum of everything passed up.
The three basic economic questions
Scarcity forces every society, whatever its political structure, to answer three fundamental questions about how it uses resources. How a society answers them defines its economic system (market, planned, or mixed).
What to produce? Which goods and services, and in what quantities — more consumer goods or more capital goods? More healthcare or more defence?
How to produce? Which methods and combinations of resources — labour-intensive or capital-intensive? What is most efficient?
For whom to produce? How output is distributed — by income, by need, or by some other criterion?
Modelling it all: the production possibilities curve
The production possibilities curve (PPC) shows the maximum combinations of two goods an economy can produce when resources are used fully and efficiently and technology is fixed. It is the single most useful diagram for making scarcity visible, and examiners reward students who can both draw it and read meaning from every part of it.
On the curve — production is efficient; the only way to get more of one good is to give up some of the other. That trade-off IS the opportunity cost.
Inside the curve — resources are unemployed or misused, so the economy produces less than it could.
Beyond the curve — currently unattainable with existing resources and technology.
The curve is usually bowed outwards because resources are not equally productive in both uses — reallocating ever-less-suitable resources raises opportunity cost (the law of increasing opportunity cost).
An outward shift of the whole curve represents economic growth — more or better resources, or improved technology.
Common mistakes examiners penalise
Confusing scarcity with poverty — scarcity affects every economy, rich or poor. Poverty is about low income; scarcity is about limited resources relative to unlimited wants.
Adding up all forgone alternatives — opportunity cost is only the SINGLE next best alternative, never the sum of everything given up.
Saying opportunity cost = the money spent — it is the value of the next best real alternative, which can differ from the cash outlay.
Confusing a movement ALONG the PPC with a SHIFT of the whole curve — moving along shows opportunity cost; the curve shifting outwards shows economic growth. Mixing these up costs marks.
Treating an inside point like a point on the curve — from inside the PPC, gaining more of one good can have zero opportunity cost, because idle resources are being brought into use.
Key concepts in this lesson
The 2022 course is built around nine key concepts. This lesson establishes three: scarcity (why economics exists), choice (its immediate consequence), and efficiency (introduced through points on versus inside the PPC). Keep these in view — an internal-assessment criterion specifically rewards linking a key concept to real-world material, and these three recur throughout the course. This lesson is identical at SL and HL; HL extension content begins in Unit 2.
Where this leads
Scarcity and opportunity cost are not just an opening topic — they are the logic behind demand, supply, market failure and every policy debate to come. When a later chapter asks whether a government should subsidise renewable energy, the real question is the same one you met here: is this the best use of scarce resources, given what must be given up?
Worked examples
See the formulas applied — reveal one step at a time, like the exam.
A student has 4 hours of free time on a Saturday afternoon. They can either study for their economics exam, which they believe will improve their grade from a 5 to a 6, or work a shift at a local café earning £12 per hour. What is the opportunity cost of choosing to study for the 4 hours?
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Identify the alternatives: (a) study or (b) work.
A government has £500 million for a new national project and has narrowed the options to two: a new high-speed rail link or 50 new schools. It chooses the rail link. What is the opportunity cost of this decision?
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Alternatives: (a) rail link or (b) 50 new schools.
A small economy produces either wheat or machines. The table shows five efficient combinations (all points on its PPC):
| Combination | Wheat (tonnes) | Machines (units) |
|---|---|---|
| A | 100 | 0 |
| B | 90 | 10 |
| C | 70 | 20 |
| D | 40 | 30 |
| E | 0 | 40 |
(a) State the opportunity cost of moving from combination B to combination C. (b) Calculate the opportunity cost of the FIRST 10 machines (A→B) and of the LAST 10 machines (D→E). What do your answers reveal about the shape of the PPC? (c) The economy currently produces 60 tonnes of wheat and 15 machines. Is this point on, inside or beyond the PPC? Justify your answer.
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(a) From B (90 wheat, 10 machines) to C (70 wheat, 20 machines): gain 10 machines, give up 20 tonnes of wheat. The opportunity cost of those 10 extra machines is 20 tonnes of wheat.
Paper 1, part (a): Explain, using a production possibilities curve (PPC) diagram, the concepts of scarcity, choice and opportunity cost. [10 marks]
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Model answer: Scarcity is the central economic problem: resources (land, labour, capital and entrepreneurship) are finite while wants are unlimited, so not all wants can be satisfied. A production possibilities curve (PPC) shows the maximum combinations of two goods — say consumer goods and capital goods — an economy can produce when all resources are used fully and efficiently with fixed technology.
How it all connects
The big idea sits in the middle — tap a linked idea to explore the link.
Tap a linked idea to see how it connects back to the main topic — that connection is what examiners reward.
Glossary
Key terms for this topic — skim now; the Check step will test them.
- scarcity
Scarcity (why economics exists), choice (its immediate consequence), and efficiency (introduced through points on versus inside the PPC).
- Choice
The act of selecting among alternatives, which is a necessary consequence of scarcity.
- Opportunity Cost
The value of the next best alternative that must be forgone when making a decision. Only the SINGLE best alternative given up counts — not the sum of all forgone options.
- Factors of Production
The scarce resources used to produce goods and services: Land (natural resources), Labour (human effort), Capital (man-made aids to production), and Entrepreneurship (organising the others and bearing risk).
- Free Good vs Economic Good
A free good is not scarce and has zero opportunity cost (e.g. air to breathe). An economic good is scarce, so obtaining it always has an opportunity cost — this covers almost everything in the course.
- The three basic economic questions
What to produce? How to produce it? For whom to produce? Every economy must answer these, and how it does so defines its economic system.
- Production possibilities curve (PPC)
A model showing the maximum combinations of two goods an economy can produce when all resources are used fully and efficiently, given fixed technology.
- On / inside / beyond the PPC
ON = productively efficient (full employment of resources). INSIDE = attainable but inefficient (unemployed/misused resources). BEYOND = currently unattainable without growth.
- Outward shift of the PPC
Economic growth: an increase in the quantity or quality of resources, or an improvement in technology, raising potential output.
- Ceteris Paribus
Latin for 'all other things being equal'. A key modelling assumption used to isolate the effect of one variable at a time.
Name it
Read the meaning, then pick which of this lesson’s terms it describes. Miss one and you see what your choice really means.
The scarce resources used to produce goods and services: Land (natural resources), Labour (human effort), Capital (man-made aids to production), and Entrepreneurship (organising the others and bearing risk).
Quick check
Write your answer first, then compare it with the model one — the gap is what you would have lost.
Teach it back
If you can explain it simply, you own it — gaps here are marks you’d lose.
Teach it back
Explain this topic as if teaching a friend. We name the gaps an examiner would still dock.
Revision flashcards
Guess first, then flip — retrieval beats re-reading.
Key takeaways
Review these before you close the topic — retrieval beats re-reading.
Scarcity exists because wants are unlimited but resources are finite.
Scarcity is universal — it affects all societies and individuals, not only the poor.
The scarce resources are the four factors of production: Land, Labour, Capital and Entrepreneurship.
Practice — then mark it
The whole point: a real Cambridge question, marked mark-by-mark.
Get a Paper 1 (a) answer marked: use a PPC to explain scarcity, choice and opportunity cost
Get a Paper 1 (a) answer marked: use a PPC to explain scarcity, choice and opportunity cost
Extra simulations & links
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Frequently asked
Checkpoint
One marked question is worth ten re-reads — close the loop before you move on.
Reading it isn’t knowing it — prove it.
Before you move on: do Get a Paper 1 (a) answer marked: use a PPC to explain scarcity, choice and opportunity cost on paper, snap a photo, and get examiner-style feedback on exactly where you win and lose marks.
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