Market

— Economics · AS Level · Price Controls, Changes in Market & Subsidy —

★ Exam Tip: The max-price 12-marker (diagram + black market + subsidy fix) has come in past papers 3–4 times — sir called it the toughest part of AS micro. Also: an 8-marker = 3 knowledge + 3 analysis + 2 evaluation. Every diagram = same 4 steps: shift the curve → new price → new quantity → new equilibrium.

Order of these notes: ① Toolkit you must know by heart ② Maximum price ③ Max price → black market (12 marks) ④ Minimum price ⑤ Changes in market (4 cases) ⑥ Incidence of subsidy ⑦ Cheat-sheet

1. Toolkit — know these by heart

① Factors affecting DEMAND (6) — they SHIFT the demand curve

Factor	Detail	Demand ↑ when…
Income	shows purchasing power; normal & inferior goods	income ↑
Direct tax	income tax = on salary; corporation tax = on company profit	direct tax ↓
Prices of related goods	substitute and complement	substitute dearer / complement cheaper
Advertisement	informative (gives info, e.g. govt on health & education) · persuasive	positive advertising
Population	more people ⇒ more demand	population ↑
Consumer taste & pattern	changes in fashion / preference	taste moves in favour

Sir: income, direct tax, related goods & advertisement are the 4 main ones; population & taste just need to be known. Learn names by heart — next classes need them.

② Factors affecting SUPPLY (4) — they SHIFT the supply curve

Factor	Effect on supply
Cost of production	cost ↓ ⇒ supply ↑ · cost ↑ ⇒ supply ↓
Technological advancement	⇒ supply ↑
Subsidy	⇒ supply ↑ (if subsidy is removed ⇒ supply ↓)
Indirect tax	(tax on goods & services) ⇒ supply ↓ (if removed ⇒ supply ↑)

③ Price vs other factors

Movement vs shiftChange in PRICE ⇒ movement along the curve (extension / contraction of QD or QS)
Change in any OTHER factor ⇒ the curve shifts
Anything increases ⇒ rightward shift · anything decreases ⇒ leftward shift

④ Laws, CS, PS, TR

Law of demand: price ↑ ⇒ I buy less; price ↓ ⇒ I buy more → negative relationship ⇒ demand curve slopes down.

Law of supply: as a producer I supply more at a higher price (more revenue/profit), less at a lower price → positive relationship ⇒ supply curve slopes up.

Consumer surplus (CS)difference between willingness to pay and actual price = area below demand curve, above price level
Producer surplus (PS)difference between minimum price and actual price = area above supply curve, below price level
Total revenueTR = price × quantity (a box)

⑤ The standard diagram (set-up used in every case)

Draw 2 axes: Price up the side, Quantity (traded) along the bottom (Q).
Demand downward, supply upward — join both to the axes (because we must mark CS & PS).
Where demand touches the axis = willingness (A). Where supply touches = minimum price (B).
Where D = S → equilibrium E → read off P and Q.

CS = PAE · PS = PBE · TR = box OPEQ (price × quantity)

2. Price Controls & Maximum Price

Price control: a price limit imposed by the government. Two kinds: maximum price (helps consumers) and minimum price (helps producers).

Maximum price: a price control imposed by the government for the benefit of the consumer.

Why? There is inflation (prices high, mehangai) in the country.
Objective: reduce inflation / make goods affordable for consumers — usually on basic necessities.
Where? Always BELOW equilibrium to be effective.

Common mistake: “maximum” does NOT mean “more”! If a pencil costs Rs 10 and govt says it must sell at Rs 8, then Rs 8 is the maximum price — it cannot be sold above that. It is a limit (a price ceiling).

Above equilibrium ⇒ INEFFECTIVE: people already find prices too high; a limit above E would make things dearer still ⇒ it fails and the market reaches back to equilibrium.

What happens (chain)

Law of demand & supply decide it: as a consumer I buy more at a lower price, as a producer I supply less at a lower price.

CS ↑ = MP·A·A′ (green) · PS ↓ = MP·B·B′ (blue) · shortage = QD − QS (red). E→A′ on D and E→B′ on S = movements

Points: A, B = willingness & min. price on the axis. A′, B′ = where the max-price line meets D and S (sir calls them “double A / double B”).

Why draw the line all the way across? In the disequilibrium diagrams we stopped the line at the curves; here price control is a limit, so we drag the straight line and label it “maximum price – effective”.

	Old (at E)	New (max price)	Change & reason
CS	P A E	MP A A′	↑ — actual price fell (willingness same)
PS	P B E	MP B B′	↓ — actual price fell (min. price same)
Revenue	O P E Q	O MP B′ QS	producer only sells QS at MP ⇒ smaller box
Shortage	—	QD − QS	the red triangle A′ E B′

Note: sir once said “PS increases” here by slip; the next class he said PS decreases — correct (triangle MP·B·B′ is smaller than PBE).

Advantages & disadvantages

✓ Advantages (4)

Lower price — goods cheaper
Total expenditure falls
CS increases
Standard of living ↑ — can afford more basic necessities

✗ Disadvantages

Black market — some stock at the low price & resell later at higher price
Shortage ⇒ must import ⇒ bad effect on BOT (balance of trade) & BOP (balance of payments)
Producer profit ↓ ⇒ demotivated ⇒ supply ↓

Example – total expenditurebefore: Rs 10 × 100 units = Rs 1000after max price: Rs 8 × 100 units = Rs 800

(Sir said “4 advantages and 3 disadvantages” in one class and “4 disadvantages” in the next — he counts BOT and BOP separately. Learn all.)

Maximum price drawn ABOVE equilibrium (just for MCQs)

line ABOVE E ⇒ price would only rise ⇒ no one buys ⇒ back to equilibrium

Consumer already can’t afford the old price; at the higher price QD → 0, so QS → 0 too ⇒ market automatically comes back to equilibrium.

Max price above E ⇒ ineffective ⇒ it reaches back to equilibrium

3. Max Price → Black Market & the Subsidy Fix

★ 12-mark question: appeared 3–4 times in past papers. It is the same max-price diagram plus 2–3 extra things — but sir said it is the toughest thing in all AS micro. Redraw it until it is automatic.

Start from the effective max-price diagram. At MP, producers supply only QS (point B′). Who gets those QS units?

First come, first served — the person who joins the queue early buys the QS units at the maximum price.
A late buyer pays more for the same quantity. Why? Some people stock goods cheap, create shortage, and resell later at a higher price.
That higher price = black-market price P*.

Example:

during COVID masks, oxygen cylinders and vaccines were hoarded cheaply, made scarce, then resold at much higher prices.

P* = price on the demand curve at QS (point C). Anyone late pays P* for the SAME quantity QS

Area	Rectangle	Meaning
Old revenue	O P E Q	at equilibrium
Revenue at max price	O MP B′ QS	legal: MP × QS
Revenue at black-market price	O P* C QS	P* × QS
Illegal revenue	MP P* C B′	govt allowed only MP, they sold at P*

The problem: govt imposed max price to fix inflation, and in doing so created another problem — the black market. Only govt can solve it. Two ways:

Leave it to the price mechanism — demand & supply forces bring the market back to equilibrium automatically.
Give a subsidy — but on QD, not QS.

Why QD and not QS? The max-price benefit must reach the consumer. Producers already earn from the black market; subsidy on QS would cut their price further and they would repeat the same trick. So aim the subsidy at the quantity demanded.

Subsidy on QD: S shifts right to S₁ through A′ ⇒ new equilibrium E₁ at price MP and quantity QD – no shortage, no black market

Subsidy ⇒ supply ↑ ⇒ S shifts right to S₁ so it passes through the QD point (A′). New minimum price = D (axis).
Old demand meets new supply at A′ ⇒ new equilibrium: price = MP, quantity = QD. Shortage gone, quantity ↑, consumer benefits.
New PS = triangle MP · D · A′ (D here is the new min-price point on the axis, not the demand curve).

✓ Storyline to write (12 marks)

Define max price; why (inflation); below E
Diagram: price ↓, QD ↑ (E→A′), QS ↓ (E→B′), shortage
CS ↑ (PAE → MP A A′), PS ↓ (PBE → MP B B′), revenue O MP B′ QS
First come first served → black market price P*, illegal revenue MP P* C B′
Govt solutions: price mechanism OR subsidy on QD ⇒ S₁, new E₁

Sir sent the written explanation paragraphs as a PDF on the class WhatsApp group (not part of these transcripts).

4. Minimum Price

Minimum price: a price control imposed by the government for the benefit of the producer.

Why? Instability in the farming market — pest/locust attacks, heavy rain, storms, strong wind ⇒ farmer loses ⇒ demotivated all year ⇒ supplies less.
Objective: raise price so the farmer is motivated to supply more (law of supply) & protect farmers’ income.
Where? Always ABOVE equilibrium to be effective.

Buffer stock = the leftover stock (the surplus).

Example (sir’s farmer):

farmer produces Rs 1 lakh worth: cost Rs 80,000, profit Rs 20,000. He sells only Rs 90,000 ⇒ Rs 10,000 of goods are left = buffer stock. Half his profit is stuck ⇒ he is demotivated again.
⇒ So the government promises to buy the leftover buffer stock at the minimum price it set, so the farmer stays motivated.

CS ↓ = MP·A·A′ · PS ↑ = MP·B·B′ · shaded red = surplus (QS − QD) = buffer stock

	Old	New	Change
CS	P A E	MP A A′	↓ (actual price ↑)
PS	P B E	MP B B′	↑ (actual price ↑, QS ↑)

Minimum price BELOW equilibrium ⇒ ineffective

line BELOW E ⇒ producer already unhappy, supplies even less ⇒ back to equilibrium

Remember (sir’s note): if minimum price is imposed below the equilibrium, it will reach back to equilibrium, i.e. it will be ineffective. The producer is already demotivated at E; a lower price would demotivate him even more, he won’t supply, so the market returns to E.

Max vs Min price

	Maximum price	Minimum price
For whom	consumer	producer (farmer)
Reason	inflation	instability in farming
Effective if	below E	above E
Result	QD > QS: shortage	QS > QD: surplus (buffer stock)
CS / PS	CS ↑, PS ↓	CS ↓, PS ↑
Side problem	black market, imports	govt must buy buffer stock

Homework 8-marker (sir’s own question, not a past paper)

8 marksanalyse using a demand & supply diagram

Explain the imposition of minimum price being effective and ineffective.

Knowledge (3): define equilibrium, minimum price (demand & supply definitions are a bonus)Analysis (3): diagrams of effective & ineffective minimum price + explanation with impact on CS and PSEvaluation (2): conclusion — price control is solved by the price mechanism, and the price mechanism is solved by price control

5. Changes in Market

Only four things can happen in a market: demand ↑ · demand ↓ · supply ↑ · supply ↓.

Who starts, who responds: demand is done by the consumer → the story starts with the consumer and the producer finishes it. Supply starts with the producer → the consumer responds.

4 steps to make the diagram① shift the curve ② new price ③ new quantity ④ new equilibrium
Check: arrows show the right shift? P and Q moved the right way? E → E₁?

Combined diagram: only the demand shift = a “shift” diagram. Only price vs QS = a “movement” diagram. We combine both in one.

Remember: shift in one curve ⇒ movement along the other.

Case 1 — Increase in demand

D → D₁ (right). P↑ Q↑. Movement along S (producer responds)

Reason: any of the 6 (income ↑, direct tax ↓, substitute dearer, complement cheaper, positive advertisement, population ↑, taste). Sir uses income ↑.

demand ↑ ⇒ shortage ⇒ price ↑ ⇒ signal to producer ⇒ at higher price he supplies more: QS extends ⇒ E → E₁.

CS: PAE → P₁CE₁ ↑ (willingness AND price both ↑). PS: PBE → P₁BE₁ ↑ (price ↑). TR: OPEQ → OP₁E₁Q₁.

Model explanation (write like this):

An increase in demand from D to D₁ due to increase in income, which will create shortage of product, causing equilibrium price to increase from P to P₁, which will provide signal to producer, so he will extend equilibrium quantity from Q to Q₁. This is how new equilibrium point is achieved from E to E₁. Also movement along supply curve shows responsiveness of producer due to changes in demand. The consumer surplus area has increased from PAE to P₁CE₁ as both the willingness and actual price have increased. The producer surplus area has also increased from PBE to P₁BE₁ as actual price has increased.

Case 2 — Decrease in demand

D → D₁ (left). P↓ Q↓. Movement along S (producer contracts)

Reason: e.g. direct tax ↑.

demand ↓ ⇒ surplus ⇒ price falls automatically ⇒ signal to producer ⇒ at lower price he supplies less: QS contracts (lower price = lower revenue).

CS: PAE → new triangle on P₁ with the new willingness C — ↓. PS: PBE → P₁BE₁ ↓. TR: OPEQ → OP₁E₁Q₁ ↓ (smaller box).

Sir wrote P₁BE₁ for both CS and PS by slip: CS uses the new willingness point C, PS uses B. Explanation = homework: copy case 1’s sentences with the opposite words.

Case 3 — Decrease in supply

S → S₁ (left). P↑ Q↓. Movement along D (consumer responds)

Reason: govt imposes indirect tax (tax on goods & services) ⇒ producer’s cost & burden ↑ ⇒ demotivated ⇒ supplies less. (Shortage ⇒ price ↑, like petrol.)

supply ↓ ⇒ shortage ⇒ price ↑ ⇒ signal to consumer ⇒ he buys less: QD contracts.

CS: PAE → P₁AE₁ ↓ (willingness same, price ↑). PS: PBE → P₁CE₁ (min. price B→C AND price both change; triangle looks smaller ⇒ ↓). TR: OPEQ → OP₁E₁Q₁.

Trick: if you can’t tell whether PS rose or fell, write “changed” — sir’s safe word.

Model explanation:

A decrease in supply from S to S₁ due to imposition of indirect tax, which will create shortage of product, causing equilibrium price to increase from P to P₁, which will provide signal to consumer, so he will contract equilibrium quantity from Q to Q₁. This is how new equilibrium point is achieved from E to E₁. Also movement along demand curve shows responsiveness of consumers due to changes in supply. The consumer surplus area has decreased from PAE to P₁AE₁ and the producer surplus area has decreased from PBE to P₁CE₁ as both the minimum price and actual price have changed.

Case 4 — Increase in supply

S → S₁ (right). P↓ Q↑. Movement along D (consumer responds)

Reasons: cost of production ↓, technology ↑, subsidy, indirect tax removed. Sir uses subsidy.

supply ↑ ⇒ surplus ⇒ price ↓ ⇒ signal to consumer ⇒ he buys more: QD extends.

S₁ drawn from slightly above the origin so the new minimum price C shows on the axis.

CS: PAE → P₁AE₁ ↑. PS: PBE → P₁CE₁ ↑. TR: OPEQ → OP₁E₁Q₁. Explanation = homework (use case 3’s template with opposite words).

Case	Shift	Gap	P	Q	Responds	Along	CS	PS
↑ Demand	D right	shortage	↑	↑	producer extends	S	↑	↑
↓ Demand	D left	surplus	↓	↓	producer contracts	S	↓	↓
↓ Supply	S left	shortage	↑	↓	consumer contracts	D	↓	changed
↑ Supply	S right	surplus	↓	↑	consumer extends	D	↑	↑

6. Incidence of Subsidy

Subsidy is a grant or cash payment given by the government to the producer. It is a factor affecting supply (not demand).

Indirect tax is a burden — the producer passes it to the consumer through higher prices. Subsidy is a benefit — the producer passes it on through lower prices. Who gets how much is decided by PED.

Earlier: vertical gap between 2 supply curves = per-unit TAX. Now = per-unit SUBSIDY, shared between consumer & producer.

Note to writeThe vertical distance between two supply curves is the per-unit subsidy, which will be shared between consumers and producers — it depends on PED.

PED link: elastic → price falls a little ⇒ QD rises a lot ⇒ TR ↑. Inelastic → price falls a lot ⇒ QD rises a little ⇒ TR ↓.

How to read the diagram

vertical gap between S and S₁ = per-unit subsidy; measured at the NEW quantity Q₁

Per-unit subsidy = vertical gap between S and S₁ — always taken from the NEW quantity Q₁ (at the old quantity there was no subsidy; supply ↑ ⇒ price ↓ ⇒ quantity ↑).
Gap at Q₁ = E₁ to D. The whole box (E₁D × Q₁) = total subsidy.
Consumer benefit = price area from P to P₁ (price fall).
Producer benefit = the area above P (rest of the box).
CS: PAE → P₁AE₁ ↑ · PS: PBE → P₁CE₁ ↑ · TR: OPEQ → OP₁E₁Q₁.

Case 1 — Elastic demand

Many substitutes; product is a luxury (want, not need) ⇒ flatter demand curve. P falls a little, Q rises a lot, TR ↑. Producer benefit > consumer benefit.

ELASTIC (flat demand): P falls a little ⇒ producer benefit > consumer benefit

Case 2 — Inelastic demand

Few substitutes; necessity (need) ⇒ steep demand curve. P falls a lot, Q rises a little, TR ↓. Consumer benefit > producer benefit.

INELASTIC (steep demand): P falls a lot ⇒ consumer benefit > producer benefit

Case 3 — Perfectly elastic demand (PED = ∞)

Thousands of substitutes making the same product at the same price ⇒ horizontal demand. Price cannot change; only way to raise revenue is to sell more units (ΔQ = ΔTR). CS = 0 (willingness = actual price). Price does not fall ⇒ only producer benefit (producer did not pass the subsidy on).

PERFECTLY ELASTIC (horizontal demand): price cannot fall ⇒ only producer benefit

Case 4 — Perfectly inelastic demand (PED = 0)

No substitutes; the firm is a price maker and can only raise revenue by raising price (no switching). Vertical demand. CS = infinite because willingness cannot be determined. Quantity unchanged, so the gap is E to E₁; price falls by the whole subsidy ⇒ only consumer benefit.

PERFECTLY INELASTIC (vertical demand): Q stays, P falls by the whole subsidy ⇒ only consumer benefit

Demand	Curve	Price falls	Q rises	Who benefits
Elastic	flat	little	a lot	producer > consumer
Inelastic	steep	a lot	little	consumer > producer
Perfectly elastic	horizontal	no change	most	only producer
Perfectly inelastic	vertical	by whole subsidy	none	only consumer

7. Full Chapter Cheat-Sheet

✓ Areas (standard diagram)

CS = PAE · PS = PBE · TR = OPEQ (A = willingness, B = min price)
Max price (below E): CS ↑ MP·A·A′ · PS ↓ MP·B·B′ · shortage QD − QS · revenue O MP B′ QS
Black market: P* at C (on D at QS) · revenue O P* C QS · illegal MP P* C B′ · fix: subsidy on QD ⇒ S₁ through A′, PS = MP·D·A′
Min price (above E): CS ↓ MP·A·A′ · PS ↑ MP·B·B′ · surplus QS − QD = buffer stock (govt buys)
Wrong side of E (max above / min below) ⇒ ineffective ⇒ back to equilibrium

✓ Changes in market & subsidy

Demand: 6 factors · Supply: 4 factors · price ⇒ movement, other factors ⇒ shift · ↑ right, ↓ left
4 steps: shift → new P → new Q → new E · consumer starts ⇒ producer responds (and vice versa)
Subsidy: S shifts right · per-unit subsidy = vertical gap at NEW Q · consumer benefit = P to P₁ · producer benefit = above P
Elastic ⇒ producer gets more · Inelastic ⇒ consumer gets more · PE ⇒ all producer · PI ⇒ all consumer
8-marker = 3 knowledge + 3 analysis + 2 evaluation