A production possibility curve turns scarcity, choice and opportunity cost into a diagram. It shows the maximum combinations of two types of output that an economy can produce with its available resources and technology. It is a model: it simplifies a whole economy to make the trade-off visible.

A production possibility curve shows the maximum possible combinations of two goods or services that can be produced when all available resources are fully and efficiently used, given current technology. One axis names one output and the other axis names a different output. The curve represents a limit: it is not a demand curve and it does not show price.

A PPC holds certain conditions constant so that one trade-off can be studied. It assumes a fixed quantity and quality of land, labour, capital and enterprise, a given level of technology, and only two categories of output. It also shows what is possible if resources are fully and efficiently used. These assumptions make the model useful, but real economies continually change.

For an exam diagram, draw clear axes starting from the same origin. Label one output on the vertical axis and the other on the horizontal axis. Draw a smooth curve sloping downwards from left to right, then label it PPC. Add points or arrows only if the question asks you to show a movement or shift.

A point on the PPC is attainable and productive efficient: the economy is producing the maximum possible output from the resources and technology assumed. A point below the PPC is attainable but inefficient or involves unused resources. A point beyond the PPC is unattainable at present because it would require more or better resources or technology.

Being below the PPC means the economy can increase both types of output without giving up either one, because resources are not fully or efficiently used. Causes can include unemployment, workers whose skills are not matched to jobs, idle factories, poor organisation, damage after a disaster or a recession. A move from below the curve to the curve is an improvement in resource use, not necessarily an increase in the quantity of resources.

A movement along a PPC reallocates existing resources between the two outputs. If more capital goods are produced, fewer consumer goods must be produced, assuming all resources were already used efficiently. The amount of the other output sacrificed is the opportunity cost of the extra output gained.

The PPC slopes downwards because the same finite resources have alternative uses. To make more of one output, some resources must be moved away from the other output. The curve is often drawn bowed out from the origin because resources are not equally suited to all tasks: a worker, machine or piece of land may be better at one type of production than another. Moving increasingly unsuitable resources can make the opportunity cost rise.

An outward shift of the whole PPC means the economy can produce more of both outputs than before. Productive potential can rise when it gains more factors of production, improves their quality or develops better technology. Examples include discovery of resources, investment in machines and infrastructure, education and training, improved healthcare, immigration of skilled workers and innovation.

An inward shift means the economy can produce less of both outputs than before. It may follow loss or damage to resources, depletion of natural resources, severe illness, emigration of workers, destruction of capital after conflict or disaster, or a fall in the quality of land and labour. It is different from moving to a point below the curve: an inward shift changes the maximum itself.

Economic growth is an increase in an economy's productive potential and, over time, its output. On a PPC, growth is shown by an outward shift. Spending some resources on capital goods, education or infrastructure can reduce current consumer output but may allow more output in the future. This is one reason why a country’s choice of output mix matters.

Before drawing, identify whether the question describes a reallocation, unused resources, more productive resources or a fall in productive potential. Then choose the appropriate visual response: a movement along the curve, a movement from below to the curve, an outward shift or an inward shift. The explanation must match the diagram exactly.