A curve showing the average total cost for different levels of output when at least input of production is fixed typically plant capacity is the short-run average cost curve

The Short-Run Average Cost (SRAC) curve illustrates the average total costs for different levels of output when at least one input of production is fixed, typically plant capacity. Here's a step-by-step explanation:

1. Identify Fixed and Variable Costs: In the short run, some factors of production are fixed. For example, the size of a factory (plant capacity) is a fixed input. On the other hand, some factors like labor or raw materials are variable and can be changed according to the level of output.

2. Calculate Total Cost: The total cost of production is the sum of fixed and variable costs.

3. Calculate Average Total Cost: The average total cost (ATC) is calculated by dividing the total cost by the quantity of output produced.

4. Plot the SRAC Curve: The SRAC curve is then plotted with the level of output on the x-axis and the average total cost on the y-axis. The curve typically slopes downwards at first, due to economies of scale, reaches a minimum point, and then slopes upwards due to diseconomies of scale.

5. Interpret the SRAC Curve: The shape of the SRAC curve reflects the law of diminishing returns. Initially, as production increases, the average total cost decreases due to the spreading of fixed costs over a larger number of units. However, after a certain point, the average total cost starts to increase as the additional cost of producing each additional unit rises. This is due to the inefficiencies created by over-utilizing the fixed inputs.