Question

Either graphically or descriptively, describe how an individual firm in a perfectly competitive market with other identical firms responds to an inward shift (decrease) in the demand curve for their product and the short run and long run implications this has for the market price and quantity. Additionally, illustrate either graphically or descriptively how the elasticity of supply for both firms and the market typically changes from the short-run to the long-run.

Answer 1

SHORT RUN

In order to maximize profits in a perfectly competitive market, firms set marginal revenue equal to marginal cost (MR=MC). MR is the slope of the revenue curve, which is also equal to the demand curve (D) and price (P). In the short-term, it is possible for economic profits to be positive, zero, or negative. When price is greater than average total cost, the firm is making a profit. When price is less than average total cost, the firm is making a loss in the market.

LONG RUN

Over the long-run, if firms in a perfectly competitive market are earning positive economic profits, more firms will enter the market, which will shift the supply curve to the right. As the supply curve shifts to the right, the equilibrium price will go down. As the price goes down, economic profits will decrease until they become zero.

When price is less than average total cost, firms are making a loss. Over the long-run, if firms in a perfectly competitive market are earning negative economic profits, more firms will leave the market, which will shift the supply curve left. As the supply curve shifts left, the price will go up. As the price goes up, economic profits will increase until they become zero.

In sum, in the long-run, companies that are engaged in a perfectly competitive market earn zero economic profits. The long-run equilibrium point for a perfectly competitive market occurs where the demand curve (price) intersects the marginal cost (MC) curve and the minimum point of the average cost (AC) curve.