Monopolistic competition — Edexcel A-Level Economics A
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Monopolistic competition explained
Diagrammatic analysis in monopolistic competition means drawing and interpreting the short-run and long-run equilibrium diagrams for a firm in this market structure.
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In the short run the firm faces a downward-sloping, relatively elastic demand (AR) curve with MR below it; profit is maximised where MC = MR, and the firm may earn supernormal profit if AR exceeds AC at that output. In the long run, free entry and exit erode profit: the demand curve shifts left until it is tangent to the AC curve at the profit-maximising output, so only normal profit remains, with price above marginal cost and output below the minimum efficient scale, giving excess capacity. You must label axes (price, cost, output), curves (AR, MR, MC, AC) and the profit-maximising point, and shade profit or loss areas correctly.
Your focus
- Draw a correctly labelled short-run equilibrium diagram for a firm in monopolistic competition.
- Draw a correctly labelled long-run equilibrium diagram showing the tangency of AR and AC.
- Interpret the diagrams to explain profit outcomes and excess capacity.
Monopolistic competition exam tips
Marking Points
- Identifies that profit is maximised where MC = MR and marks this output correctly on the diagram.
- Draws a downward-sloping AR curve with MR below AR, reflecting price-setting power in monopolistic competition.
- Shows short-run supernormal profit as the rectangle between AR and AC at the profit-maximising output.
- Explains that long-run equilibrium occurs where AR is tangent to AC, giving only normal profit.
- Recognises that in long-run equilibrium price exceeds marginal cost and output is below minimum efficient scale, indicating excess capacity.
- Correctly labels axes, curves and key points, and distinguishes short-run from long-run diagrams.
Examiner Tips
- 💡Practise drawing both short-run and long-run diagrams side by side so you can contrast profit outcomes quickly.
- 💡Always label axes, curves and the MC = MR point; unlabelled diagrams lose marks.
- 💡Use the tangent condition (AR tangent to AC) to justify the long-run normal-profit outcome in written answers.
Common Mistakes
- Drawing a horizontal AR curve as if the firm were perfectly competitive; correction: in monopolistic competition the firm faces a downward-sloping demand curve because of product differentiation.
- Placing MR above AR; correction: MR must lie below AR for a downward-sloping linear demand curve.
- Showing supernormal profit in long-run equilibrium; correction: free entry shifts demand left until AR is tangent to AC, leaving only normal profit.
- Forgetting to label the profit-maximising output where MC = MR; correction: always mark and label this point and the associated price and quantity.