Market Forms and Price Determination
Market structure determines how price and output are set. The exam tests the features of the four forms and the equilibrium condition of the firm, often with a numerical or diagram-based question.
Core rules
- Perfect competition: many buyers and sellers, homogeneous product, free entry and exit, perfect knowledge; the firm is a price taker, so AR = MR = P (horizontal line).
- Monopoly: single seller, no close substitute, barriers to entry, price maker; may practise price discrimination.
- Monopolistic competition: many firms, differentiated products, selling costs, downward-sloping demand.
- Oligopoly: few large firms, interdependence, price rigidity (kinked demand curve).
- Equilibrium of the firm: MR = MC, and MC must be rising. In the short run a firm shuts down if price falls below minimum AVC; break-even is where price equals minimum AC.
Worked example
A perfectly competitive firm sells at ₹20 per unit. Its MC schedule is: 1st unit ₹12, 2nd ₹16, 3rd ₹20, 4th ₹26. At 3 units MR = MC = ₹20 and MC is rising afterwards, so equilibrium output is 3 units. If AVC at 3 units were ₹22 - above price - the firm would shut down despite MR = MC, because variable cost is not covered.
Traps that cost marks
- Writing that a monopoly can charge any price it likes; demand still constrains it.
- Using MR = MC alone without checking that MC is rising, which marks a profit minimum rather than a maximum.
- Confusing break-even (P = AC, normal profit) with shut-down (P = minimum AVC).
- Describing monopolistic competition as a homogeneous product market - differentiation is its defining feature.