## A2 Economics: Micro – Long-Run Average Cost – Envelope Curve

Another post geared towards the A2 exam next week. Long-run and short-run average costs curves are part of economies of scale and market structures essays.

In the short run at least one factor of production is fixed but In the long run the firm can alter all of its inputs, using greater quantities of any of the factors of production. It is now operating on a larger scale. So all of the factors of production are variable in the long run. In the very long run, technological change can alter the way the entire production process is organised, including the nature of the products themselves. In a society with rapid technological progress this will shrink the time period between the short run and the long run.

The long-run average cost (LAC) curve shows the least costly combination of producing any particular quantity. The graph below shows short-run average costs (SATC) and the LAC. The LAC forms a tangent with the SATC and it is therefore the lowest possible average cost for each level of output where the factors of production are all variable – it is formed from a series of SATC curves. The diagram shows:

From the diagram A is the least-cost way to make output Q1 in the short run. B is the least-cost way to make an output Q2. It must be more costly to make Q2 using the wrong combination of factors of production, for example the quantity corresponding to point E. For the combination of factors of production at A, SATC1 shows the cost of producing each output, including Q2. Hence SATC1 must lie above LAC at every point except A, the output level for which the combination of factors of production is best

The LAC is a flatter U-shape than the SATC curves and can be explained by economies of scale and diseconomies of scale. However it is really important to note that the firm does not necessarily produce at the minimum point on each of its SATC curves. Thus the LAC curve shows the minimum average cost way to produce a given output when all factors can be varied, not the minimum average cost at which a given plant can produce.
Note:

The Long-Run Average Cost is sometimes abbreviated to LRAC
The Short-Run Average Cost is sometimes abbreviated to SRAC

This LAC is also know as the envelope curve (looks similar to the back of an old style envelope) – see image.

Source: Economics by Begg 7th Edition