Key Points

A perfectly competitive market is characterized by a large number of buyers and sellers, homogenous products, free entry and exit for firms, and perfect information among all participants.

The defining characteristic of perfect competition is price-taking behavior. Individual firms and buyers must accept the market price and cannot influence it because they are too small relative to the market.

For a price-taking firm, the market price (p) is equal to its Average Revenue (AR) and its Marginal Revenue (MR). Therefore, the relationship is p = AR = MR.

The demand curve facing an individual firm in a perfectly competitive market is a horizontal line at the market price. This indicates that the demand is perfectly elastic.

The primary assumption is that a firm aims to maximize its profit. Profit is calculated as the difference between Total Revenue (TR) and Total Cost (TC).

A firm's profit is maximized at the level of output where Marginal Revenue (MR) equals Marginal Cost (MC). In perfect competition, this condition becomes Price (p) equals Marginal Cost (MC).

At the profit-maximizing output level, the Marginal Cost (MC) must be non-decreasing. The MC curve cannot be downward sloping at the point where it intersects with the price line.

In the short run, a firm will only produce a positive level of output if the market price (p) is greater than or equal to the minimum Average Variable Cost (AVC).

In the long run, a firm will only produce a positive level of output if the market price (p) is greater than or equal to the minimum Long-Run Average Cost (LRAC).

A firm's short-run supply curve is the rising portion of its Short-Run Marginal Cost (SMC) curve from and above the minimum point of the Average Variable Cost (AVC) curve.

A firm's long-run supply curve is the rising portion of its Long-Run Marginal Cost (LRMC) curve from and above the minimum point of the Long-Run Average Cost (LRAC) curve.

The shutdown point is the minimum of the AVC curve, below which the firm stops producing in the short run. The break-even point is the minimum of the AC curve, where the firm earns only normal profit.

A firm's supply curve can shift due to technological progress or changes in input prices. Technological progress shifts the supply curve rightward, while an increase in input prices shifts it leftward.

The market supply curve is the horizontal summation of the individual supply curves of all firms in the market. An increase in the number of firms shifts the market supply curve to the right.

Price elasticity of supply measures the responsiveness of quantity supplied to a change in price. It is calculated as the percentage change in quantity supplied divided by the percentage change in price.