The Theory of the Firm under Perfect Competition
Class 12 · Economics
4 ideas in Class 12 Economics, explained in plain words, with games and quizzes to practise.
Perfect Competition and Revenue
Part of: Taking the Price
Perfect competition needs many small buyers and sellers, identical goods, free entry and exit, and full information. The result is price taking: above the market price nothing sells, at or below it any amount sells. With candles at 12 rupees, TR runs 0, 12, 24, 36, 48, 60; AR and MR both equal 12 at every output.
Why it matters. Farm and stock markets behave nearly this way. Learners who can spot the four features know when a seller truly cannot set prices and how revenue grows box by box.
Formulas
- TR = price x quantity
- AR = TR / q = price
- MR = change in TR / change in q = price
- Worked candles: price 12; TR at 3 = 36; TR at 5 = 60
Key words
- Perfect competition
- : Market with many sellers of one identical good.
- Homogeneous product
- : Identical product across all firms.
- Free entry and exit
- : Firms can enter and leave freely.
- Perfect information
- : Everyone knows prices and quality fully.
- Price taking
- : Accepting the market price as given.
- Total revenue
- : Price times quantity sold.
- Average revenue
- : Revenue per unit, equal to price.
- Marginal revenue
- : Extra revenue from one more unit, equal to price.
Try it in two minutes
- Ask the child what happens if one vegetable seller doubles price.
- Ask why buyers can switch sellers freely.
- Explain that revenue is simply price times boxes sold.
Try at home. Pick a roadside market and test it against the four features.
Three Conditions for Maximum Profit
Part of: Chasing Maximum Profit
Profit peaks where MR equals MC: while MR tops MC each extra unit adds profit, after that each subtracts. For price takers MR is price, so p equals MC on a non-falling MC stretch. The firm also needs price above AVC in the short run and above AC in the long run; with price 12, output 6 and cost 60, profit is 72 minus 60, which is 12.
Why it matters. Every production target is this calculation. Learners who can test the three conditions know exactly when to expand, hold, or shut down.
Formulas
- Profit = TR - TC
- Maximum where MR = MC
- Competitive peak where price = MC
- Stay open short run only if price >= AVC; long run only if price >= AC
Key words
- Profit
- : Revenue minus total cost.
- Marginal revenue
- : Extra revenue from one more unit.
- Marginal cost
- : Extra cost of one more unit.
- Condition one
- : Price must equal marginal cost.
- Condition two
- : MC must be rising at the peak.
- Condition three
- : Price must cover AVC short run, AC long run.
- Profit rectangle
- : Areas of revenue and cost rectangles.
- Normal profit
- : Normal earnings counted inside costs.
Try it in two minutes
- Ask the child when making one more unit pays.
- Ask why a falling-cost crossing cannot be the peak.
- Explain that covering variable cost keeps doors open.
Try at home. With price 12 and a cost list, find the output where extras match.
The Firm's Supply Curve
Part of: From Firm to Market
Short run supply is the rising SMC from min AVC upward, zero below; long run supply is rising LRMC from min LRAC upward, zero below. The shutdown point is min AVC short run and min LRAC long run; break-even is min AC where only normal profit is earned. Better methods shift supply right, dearer inputs or a unit tax shift it left.
Why it matters. Every price-output quote a firm gives comes off this line. Learners who can draw it and shift it predict how tools, wages and taxes move what firms sell.
Formulas
- Short run supply = SMC above min AVC
- Long run supply = LRMC above min LRAC
- Unit tax of t lifts MC and AC by t at each output
- Shutdown short run at min AVC; long run at min AC
Key words
- Short run supply curve
- : Rising SMC above min AVC, else zero.
- Long run supply curve
- : Rising LRMC above min LRAC, else zero.
- Shutdown point
- : Min AVC point; produce nothing below.
- Break-even point
- : Min AC point; only normal profit there.
- Technological progress
- : Output choice shifting after better methods.
- Input price rise
- : Output choice shifting after dearer inputs.
- Unit tax
- : Per-unit levy lifting all cost lines.
- Normal profit
- : Minimum keep-going earning inside costs.
Try it in two minutes
- Ask the child when selling starts as price rises.
- Ask what a new machine does to the line.
- Explain that a per-unit tax lifts every cost step.
Try at home. Sketch SMC and AVC and darken the supply part.
Market Supply and Elasticity of Supply
Part of: From Firm to Market
Market supply horizontally sums firm supplies: with S1 = p minus 12 above 12 and S2 = p minus 18 above 18, market is p minus 12 between 12 and 18, then 2p minus 30 above 18; at 20 that is 8 plus 2, which is 10. Elasticity divides percentage quantity change by percentage price change: balls from 400 at 20 to 1600 at 40 give 300 over 100, which is 3. Lines through the origin are unit elastic; price-side cuts exceed one; quantity-side cuts trail below one.
Why it matters. Every market forecast adds supplies and gauges reactions. Learners who can sum lines and score reactions predict how prices move quantities across whole markets.
Formulas
- Market supply = sum of firm supplies at each price
- S1: p - 12 above 12; S2: p - 18 above 18; market 2p - 30 above 18
- Elasticity = (change in Q / Q) / (change in P / P)
- Worked balls: price 20 to 40, 400 to 1600: elasticity 3
Key words
- Market supply
- : Sum of all firms' supplies at each price.
- Horizontal summation
- : Sideways addition of firm curves.
- Price elasticity of supply
- : Percentage supply change over percentage price change.
- Perfectly inelastic supply
- : Supply ignoring price: vertical line.
- Unit elastic supply
- : Supply through the origin: elasticity one.
- Elastic supply curve
- : Curve cut from price side: elasticity above one.
- Inelastic supply curve
- : Curve cut from quantity side: elasticity below one.
- Entry effect
- : More firms shifting market supply right.
Try it in two minutes
- Ask the child to add both firms' sales at one price.
- Ask how strongly sales react to price.
- Explain that the origin line reacts one for one.
Try at home. Add two invented supply lines and find the kink price.
What your child will practise
- Market Supply and Elasticity of Supply: Jungle Quick Fire (Quick Fire)
- Perfect Competition and Revenue: Candy Quick Fire (Quick Fire)
- Perfect Competition and Revenue: Space Puzzle (Clue Puzzle)
- The Firm's Supply Curve: Desert Quick Fire (Quick Fire)
- Three Conditions for Maximum Profit: Jungle Puzzle (Clue Puzzle)
- Quiz: Market Supply and Elasticity of Supply (8 questions)
- Quiz: Perfect Competition and Revenue (8 questions)
- Quiz: The Firm's Supply Curve (8 questions)
- Quiz: Three Conditions for Maximum Profit (8 questions)