CBSE Class 12 Microeconomics Revision Notes Chapter 4 The Theory of the Firm Under Perfect Competition

Perfect competition is a market structure where many firms sell homogeneous products and each firm accepts the market price. In Class 12 Microeconomics, this chapter explains price-taking behaviour, revenue, profit maximisation, firm supply, market supply and elasticity of supply.

The Theory of the Firm Under Perfect Competition studies how a firm decides the quantity it should produce. The chapter assumes that a firm wants to maximise profit. Since a firm under perfect competition cannot change the market price, it chooses the output level where its profit is the highest.

Use these CBSE Class 12 Microeconomics Revision Notes Chapter 4 for the 2026–27 academic year to revise perfect competition, price line, revenue, profit maximisation, shutdown point, break-even point, supply curve and price elasticity of supply. These notes keep formulas, conditions and curve logic together for quick revision.

Key Takeaways

• Perfect competition: A market with many buyers, many sellers, homogeneous products, free entry and perfect information.
• Price taker: A firm accepts the price fixed by the industry and only decides output.
• Revenue result: Under perfect competition, MR = AR = Price.
• Profit maximisation: A firm produces where Price = MC, MC is rising, and price covers the relevant average cost.

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Access Class 12 Microeconomics Chapter 4 The Theory of the Firm Under Perfect Competition Notes in 30 Minutes

Revise this chapter as a firm’s decision chain.

Market structure → Price-taking → Revenue → Profit maximisation → Supply curve → Market supply → Elasticity

The Theory of the Firm Under Perfect Competition Class 12 Notes: Chapter Overview

This chapter studies the behaviour of a firm under perfect competition. It asks one central question:

How much output should a firm produce?

The answer depends on profit. A firm compares revenue and cost. It produces the quantity where profit is maximum.

Formula:

Profit = Total Revenue - Total Cost

or

π = TR - TC

The chapter uses three important assumptions.

Perfect Competition in Class 12 Microeconomics Chapter 4 Notes

Perfect competition is a market structure in which a large number of buyers and sellers trade a homogeneous product.

No single buyer or seller can influence the market price. The price is decided by the industry through demand and supply.

Meaning of Perfect Competition

Perfect competition refers to a market where:

• There are many buyers and sellers.
• All firms sell identical products.
• Firms can freely enter or leave the market.
• Buyers and sellers have complete market information.

A firm under perfect competition is a price taker. It accepts the price determined by the market.

Features of Perfect Competition

Large Number of Buyers and Sellers

There are so many buyers and sellers that one firm’s output is very small compared to the total market output.

So, one firm cannot change market supply enough to influence price.

Homogeneous Product

A homogeneous product means the product of one firm is identical to the product of another firm.

For buyers, there is no difference between the goods sold by different firms. This keeps the price same for all firms.

Free Entry and Exit

New firms can enter the market when profits are high. Existing firms can leave when losses continue.

This feature is important in the long run because it helps remove abnormal profits and losses.

Perfect Information

Perfect information means buyers and sellers know the market price and product quality.

A seller cannot charge a higher price because buyers already know the market price.

Why a Firm Is a Price Taker

A firm under perfect competition is a price taker because it cannot fix its own price.

If it charges a price higher than the market price, buyers shift to other firms. Since all firms sell identical products, the firm loses all customers.

If it charges a price lower than the market price, it earns less revenue unnecessarily. It can already sell any quantity at the market price.

So, the firm accepts the market price and decides only the quantity to produce.

Price Line, Demand Curve, AR and MR Under Perfect Competition

The price line is the same as the demand curve faced by a firm under perfect competition.

Since the firm can sell any quantity at the market price, its demand curve is perfectly elastic.

Price Line

The price line is a horizontal straight line at the market price.

It shows that price remains constant for the firm at every output level.

Revenue Under Perfect Competition

Revenue is the money earned by a firm from selling its output.

There are three main revenue concepts:

• Total Revenue
• Average Revenue
• Marginal Revenue

Total Revenue

Total Revenue is the total money received from selling a given quantity of output.

Formula:

TR = Price × Quantity

or

TR = p × q

Example:
If price is ₹10 and the firm sells 5 units:

TR = 10 × 5 = ₹50

Total Revenue Curve

Under perfect competition, price remains constant.

So, TR increases at a constant rate as output increases. The TR curve is an upward-sloping straight line from the origin.

Average Revenue

Average Revenue is revenue per unit of output.

Formula:

AR = TR / q

Since TR = p × q:

AR = p × q / q

AR = p

So, under perfect competition:

AR = Price

Marginal Revenue

Marginal Revenue is the additional revenue earned by selling one more unit of output.

Formula:

MR = Change in TR / Change in Quantity

Since every extra unit is sold at the same market price:

MR = Price

Why MR = AR = Price

Under perfect competition, the firm sells every unit at the same market price.

So:

MR = AR = p

Profit Maximisation by a Firm

A firm aims to produce the level of output where profit is maximum.

Formula:

Profit = TR - TC

or

π = TR - TC

A firm compares marginal revenue and marginal cost to decide output.

Condition 1: Price = MC

A perfectly competitive firm maximises profit where:

Price = Marginal Cost

Since MR = Price:

MR = MC

or

P = MC

Why P = MC Is Needed

If MR > MC, the firm can increase profit by producing more.

If MR < MC, the firm can increase profit by producing less.

So, profit is maximum where MR = MC.

Under perfect competition:

P = MC

Condition 2: MC Must Be Non-Decreasing

The firm does not choose output where MC is falling.

For maximum profit, MC should be rising or non-decreasing at the equilibrium output.

This means the MC curve should cut the MR curve from below.

Condition 3: Price Must Cover Relevant Average Cost

The third condition depends on the time period.

In the short run, the firm may continue even if it cannot cover total cost, as long as it covers variable cost.

In the long run, the firm must cover total cost to remain in the industry.

Short-Run Profit Maximisation

In the short run, fixed costs already exist. The firm decides whether it should produce or shut down temporarily.

A firm produces in the short run if:

P = SMC

SMC is rising

P ≥ AVC

If price is less than AVC, the firm shuts down.

Short-Run Decision Table

Long-Run Profit Maximisation

In the long run, all costs are variable. A firm continues only when price covers long-run average cost.

A firm produces in the long run if:

P = LRMC

LRMC is rising

P ≥ LRAC

If price is less than LRAC, the firm exits the industry.

Long-Run Decision Table

Normal Profit, Break-Even Point and Shutdown Point

These three concepts are often confused. They refer to different firm situations.

Normal Profit

Normal profit is the minimum profit needed to keep a firm in business.

In economics, normal profit is treated as part of cost.

A firm earns normal profit when:

AR = AC

or

TR = TC

Break-Even Point

The break-even point is the point where a firm covers all its costs and earns normal profit.

Formula:

TR = TC

or

AR = AC

At this point, the firm has no abnormal profit and no loss.

Shutdown Point

The shutdown point is the point where price equals minimum average variable cost in the short run.

Formula:

Price = Minimum AVC

or

AR = AVC

Below this point, the firm cannot cover variable cost and stops production in the short run.

Break-Even Point vs Shutdown Point

Supply Curve of a Firm Under Perfect Competition

Supply is the quantity of a commodity a firm is willing to sell at different prices, given technology and factor prices.

A supply schedule shows price and quantity supplied in table form.

A supply curve shows the same relationship graphically.

Meaning of Firm Supply

A firm’s supply is the quantity it chooses to produce and sell at a given price.

Under perfect competition, the firm chooses output where price equals marginal cost, subject to shutdown conditions.

Short-Run Supply Curve of a Firm

The short-run supply curve of a firm is the rising part of the short-run marginal cost curve from and above the minimum AVC.

This means:

• If price is below minimum AVC, supply is zero.
• If price is equal to or above minimum AVC, supply is found where P = SMC.

Short-Run Supply Rule

So, the short-run supply curve includes:

Rising SMC above minimum AVC + zero output below minimum AVC

Long-Run Supply Curve of a Firm

The long-run supply curve of a firm is the rising part of the long-run marginal cost curve from and above the minimum LRAC.

This means:

• If price is below minimum LRAC, the firm exits.
• If price is equal to or above minimum LRAC, the firm produces where P = LRMC.

Long-Run Supply Rule

So, the long-run supply curve includes:

Rising LRMC above minimum LRAC + zero output below minimum LRAC

Short-Run and Long-Run Supply Curve Difference Table

Determinants of a Firm’s Supply Curve

A firm’s supply curve can shift when factors affecting marginal cost change.

Technology

Improved technology reduces cost of production.

When cost falls, the firm can supply more at the same price. The supply curve shifts right.

Input Prices

If input prices rise, cost of production rises.

This reduces supply and shifts the supply curve left.

Unit Tax

A unit tax increases cost per unit.

This raises marginal cost and reduces supply.

Price Expectations

If firms expect prices to rise in the future, they may reduce current supply and hold stock for later sale.

Determinants of Supply Table

Market Supply Curve

Market supply is the total quantity supplied by all firms in the market at a given price.

It is obtained by adding the supply of all individual firms at each price.

Individual Supply and Market Supply

If there are three firms in a market:

Market Supply = Firm A Supply + Firm B Supply + Firm C Supply

The market supply curve is the horizontal summation of individual supply curves.

Shift in Market Supply

Market supply changes when:

• Number of firms changes
• Technology changes
• Input prices change
• Taxes or subsidies change
• Expectations about future prices change

Price Elasticity of Supply

Price elasticity of supply measures how responsive quantity supplied is to a change in price.

Formula:

Price Elasticity of Supply = Percentage Change in Quantity Supplied / Percentage Change in Price

or

es = %ΔQs / %ΔP

Since price and quantity supplied usually move in the same direction, price elasticity of supply is generally positive.

Types of Price Elasticity of Supply

Extreme Cases of Supply Elasticity

Elasticity of Supply Quick Check

Quick Revision Tables for The Theory of the Firm Under Perfect Competition

Perfect Competition Feature Table

Revenue Formula Table

Profit Maximisation Table

Supply Curve Table

Decision Rule Table

Important Terms in Chapter 4

Common Mistakes in Microeconomics Chapter 4 Class 12 Notes

Useful Links for Class 12 Microeconomics