The Theory of the Firm under Perfect Competition Class 12 Notes Explained

Introduction to The Theory of the Firm under Perfect Competition

The Theory of the Firm under Perfect Competition class 12 notes begin with understanding the market structure known as perfect competition. In this market:

• There are many buyers and sellers
• Products are homogeneous (identical)
• Firms are price takers, meaning they cannot influence the market price
• There is free entry and exit of firms
• Perfect knowledge is available to all participants

This setup helps explain how firms decide the quantity to produce and the price to accept. The theory analyses how firms maximise profits and how market forces drive the equilibrium price and quantity.

Cost Concepts and Revenue in Perfect Competition

Understanding the costs and revenues is key to mastering this chapter. The main cost concepts include:

• Total Cost (TC): Sum of fixed and variable costs
• Fixed Cost (FC): Costs that do not change with output
• Variable Cost (VC): Costs that vary with output
• Average Cost (AC): $AC = \frac{TC}{Q}$
• Marginal Cost (MC): Cost of producing one additional unit, $MC = \frac{\Delta TC}{\Delta Q}$

Revenue concepts:

• Total Revenue (TR): Price multiplied by quantity, $TR = P \times Q$
• Average Revenue (AR): Revenue per unit, $AR = \frac{TR}{Q}$
• Marginal Revenue (MR): Revenue from selling one more unit, $MR = \frac{\Delta TR}{\Delta Q}$

In perfect competition, price $P$ equals AR and MR because firms are price takers.

Short-Run Equilibrium of the Firm under Perfect Competition

In the short run, firms can earn supernormal profits, normal profits, or incur losses. The equilibrium condition for profit maximisation is:

$$ MC = MR = P $$

Key points:

• If $P > AC$, the firm earns supernormal profits.
• If $P = AC$, the firm earns normal profits (break-even).
• If $P < AC$ but $P > AVC$, the firm incurs losses but continues to operate.
• If $P < AVC$, the firm shuts down temporarily.

Worked Example:

If a firm’s MC at 100 units is ₹50 and the market price is ₹50, the firm should produce 100 units to maximise profit because $MC = MR = P$.

Long-Run Equilibrium and Market Adjustment

In the long run, firms can enter or exit the market freely. The long-run equilibrium occurs when firms earn normal profits, meaning:

$$ P = MC = AC $$

This condition ensures:

• No incentive for firms to enter or leave the industry
• Firms produce at minimum average cost, ensuring productive efficiency

If firms earn supernormal profits, new firms enter, increasing supply and reducing price. If firms incur losses, some exit, reducing supply and increasing price until normal profits are restored.

Comparison of Short-Run and Long-Run Equilibrium

Understanding the differences between short-run and long-run equilibrium is essential:

This comparison helps students understand market dynamics over time.

Important Diagrams and Formulas to Remember

Diagrams are crucial for visualising concepts:

• Cost Curves: MC, AC, AVC
• Revenue Curves: AR and MR (horizontal at market price)
• Equilibrium Point: Intersection of MC and MR

Key formulas:

• $AC = \frac{TC}{Q}$
• $MC = \frac{\Delta TC}{\Delta Q}$
• $TR = P \times Q$
• $MR = \frac{\Delta TR}{\Delta Q}$

Worked Example:

If a firm’s total cost at 50 units is ₹2000 and at 51 units is ₹2040, then:

$$ MC = TC_{51} - TC_{50} = 2040 - 2000 = ₹40 $$

If market price is ₹40, producing 51 units is profit-maximising.