01 · Explore
Defining Features of Perfect Competition
Perfect competition describes a specific market environment where individual buyers and sellers have no power to influence market prices.
A perfectly competitive market is characterized by a large number of buyers and sellers, where each individual is very small relative to the total market size. This ensures that no single participant can dictate the price. Furthermore, all firms produce a homogenous product, meaning the goods are identical and interchangeable from the buyer's perspective.
Two other critical features are free entry and exit for firms and perfect information. Free entry ensures that the number of firms can adjust based on profitability, while perfect information means all participants are fully aware of prices and product quality. These conditions lead to 'price-taking' behaviour, where firms must accept the prevailing market price determined by the industry.
If a price-taking firm attempts to charge even slightly more than the market price, it will lose all its customers to competitors. Conversely, there is no incentive to charge less, as the firm can sell any quantity it desires at the existing market price. Thus, the demand curve facing an individual firm is perfectly elastic, represented as a horizontal line.
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Why is a firm under perfect competition called a 'price-taker'?
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02 · Explore
Total, Average, and Marginal Revenue
Revenue is the money a firm earns by selling its output. In perfect competition, the relationship between price and revenue is unique.
Total Revenue (TR) is calculated by multiplying the market price (p) by the quantity sold (q). Since the price is constant for a price-taker, the TR curve is an upward-sloping straight line starting from the origin. The slope of this line is equal to the market price.
Average Revenue (AR) is the revenue earned per unit of output, defined as TR/q. For a competitive firm, AR = (p × q) / q = p. Marginal Revenue (MR) is the change in total revenue resulting from selling one additional unit. Since every extra unit is sold at the same market price 'p', the MR is also equal to 'p'.
In a perfectly competitive market, the relationship p = AR = MR holds true. This means the price line, which is horizontal, represents both the average and marginal revenue for the firm.
| Quantity (q) | Price (p) | Total Revenue (TR) | Marginal Revenue (MR) |
|---|---|---|---|
| 0 | 10 | 0 | - |
| 1 | 10 | 10 | 10 |
| 2 | 10 | 20 | 10 |
| 3 | 10 | 30 | 10 |
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If a firm sells 10 units at a market price of Rs 25, what are its AR and MR?
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03 · Explore
Conditions for Profit Maximisation
A firm is assumed to be a 'ruthless profit maximiser,' choosing an output level where the gap between total revenue and total cost is greatest.
Profit (π) is defined as the difference between Total Revenue (TR) and Total Cost (TC). To find the output level (q₀) that maximises profit, three conditions must be met. First, the market price (p) must equal the Marginal Cost (MC). If MR > MC, the firm can increase profit by producing more; if MR < MC, it should produce less.
The second condition is that the Marginal Cost must be non-decreasing at the chosen output level. This means the MC curve should be upward-sloping or flat at q₀. If MC is falling, the firm could still increase profits by expanding production further.
The third condition relates to the firm's ability to cover its costs. In the short run, the price must be greater than or equal to the Average Variable Cost (p ≥ AVC). In the long run, since all costs are variable, the price must be greater than or equal to the Average Cost (p ≥ AC).
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Why won't a firm produce at a point where MC is falling?
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04 · Explore
The Short Run Supply Curve
A firm's supply curve shows how much it is willing to produce at different price levels.
In the short run, a firm faces both fixed and variable costs. The firm will only produce if the price it receives covers at least its variable costs. If the price falls below the minimum Average Variable Cost (AVC), the firm will produce zero output to minimize losses. This point is known as the 'shut down point'.
For any price equal to or above the minimum AVC, the firm will produce the output where p = SMC (Short-run Marginal Cost). Therefore, the short-run supply curve is the rising part of the SMC curve starting from the minimum point of the AVC curve.
At prices below the minimum AVC, the supply is zero. This creates a supply curve that follows the vertical axis at q=0 until the shut-down price is reached, and then follows the SMC curve.
Deriving Short Run Supply
- 1
Price < Min AVC
The firm cannot cover variable costs; output is zero.
- 2
Price = Min AVC
The shut-down point; the firm is indifferent between producing and closing.
- 3
Price > Min AVC
The firm produces where P = SMC on the rising part of the curve.
The sequence shows how a firm determines its supply based on the relationship between market price and variable costs.
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What is the shut-down point in the short run?
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05 · Explore
The Long Run Supply Curve
In the long run, all costs are variable, and firms must cover their total average costs to stay in business.
The long-run supply curve is derived similarly to the short-run curve, but it uses Long-run Marginal Cost (LRMC) and Long-run Average Cost (LRAC). A firm will only stay in the market if the price is at least equal to the minimum LRAC. If the price is lower, the firm earns less than 'normal profit' and will exit the industry.
The long-run supply curve is the rising part of the LRMC curve from and above the minimum of the LRAC curve. For all prices strictly below the minimum LRAC, the firm's supply is zero.
Normal profit is the minimum level of profit required to keep a firm in its current business and is considered a part of total costs (an opportunity cost). Profits earned above this level are called super-normal profits.
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What is the 'Break-even Point'?
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06 · Explore
Determinants of the Supply Curve
Supply is not static; it shifts based on changes in technology, input prices, and government policy.
Technological progress allows a firm to produce the same output using fewer inputs. This reduces the marginal cost of production, shifting the MC curve (and thus the supply curve) to the right. At any given price, the firm is now willing to supply more units.
Conversely, an increase in input prices, such as higher wages or raw material costs, increases the cost of production. This shifts the MC curve to the left, meaning the firm will supply fewer units at any given price.
Government intervention through a unit tax also affects supply. A unit tax of 't' per unit increases the firm's marginal and average costs by exactly 't'. This shifts the supply curve to the left (upward), as the firm now requires a higher price to supply the same quantity.
Impact of a Unit Tax
MC_new = MC_old + t
If a firm's marginal cost was Rs 50 and the government imposes a unit tax of Rs 5, the new marginal cost becomes Rs 55. To maintain the P=MC condition, the firm will now produce less at the original market price, shifting the supply curve leftward.
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How does an increase in the price of an input affect the supply curve?
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07 · Explore
Market Supply Curve
The market supply curve represents the total quantity all firms in an industry are willing to sell at various prices.
The market supply curve is obtained by the horizontal summation of the supply curves of all individual firms in the market. For any given price, we add together the quantities supplied by each firm to find the total market supply.
Consider a market with two firms, Firm A and Firm B. If at a price of Rs 10, Firm A supplies 5 units and Firm B supplies 8 units, the market supply at Rs 10 is 13 units. This process is repeated for all possible prices to plot the market supply curve.
The market supply curve also shifts if the number of firms in the industry changes. An increase in the number of firms shifts the market supply curve to the right, while a decrease shifts it to the left.
Calculating Market Supply
Sm(p) = p - 10 for 10 <= p < 15; Sm(p) = 2p - 25 for p >= 15
If Firm 1's supply is (p - 10) for p >= 10 and Firm 2's supply is (p - 15) for p >= 15, then for prices between 10 and 15, only Firm 1 supplies. At p = 20: Firm 1 supplies 20-10=10 units; Firm 2 supplies 20-15=5 units. Total Market Supply = 10 + 5 = 15 units, which matches the aggregate formula 2(20) - 25 = 15.
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Question
If there are 100 identical firms each supplying 20 units at a price of Rs 50, what is the market supply?
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08 · Explore
Price Elasticity of Supply
Elasticity measures how sensitive the quantity supplied is to a change in the market price.
The price elasticity of supply (eS) is defined as the percentage change in quantity supplied divided by the percentage change in price. It is a unit-free measure. If eS > 1, supply is elastic; if eS < 1, supply is inelastic; and if eS = 1, it is unitary elastic.
The formula is eS = (ΔQ/Q) / (ΔP/P), which simplifies to (ΔQ/ΔP) × (P/Q). Geometrically, for a straight-line supply curve, if the line intercepts the price axis (Y-axis), eS > 1. If it intercepts the quantity axis (X-axis), eS < 1. If it passes through the origin, eS = 1 at all points.
A vertical supply curve has an elasticity of zero (perfectly inelastic), meaning quantity supplied does not change regardless of price. A horizontal supply curve has infinite elasticity (perfectly elastic).
Calculating Elasticity
eS = (Percentage change in quantity) / (Percentage change in price)
Price rises from Rs 10 to Rs 30 (ΔP=20, %ΔP=200). Quantity rises from 200 to 1000 units (ΔQ=800, %ΔQ=400). Following the source's percentage method: eS = 400 / 200 = 2. Since 2 > 1, the supply is elastic.
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Question
What is the elasticity of a straight-line supply curve passing through the origin?
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