Class 11 Micro Economics Notes · CBSE

Movement along and Shift in Supply Curve

Movement along and Shift in Supply Curve — understanding expansion, contraction, and rightward and leftward shifts of the supply curve. CBSE Class 11 Microeconomics notes with graphs and comparisons.

Last updated: 16 Sep 2026

Notes

Movement along the Supply Curve (Change in Quantity Supplied)

Change in Quantity Supplied

When the quantity supplied of a commodity changes due to a change in its own price, keeping other factors constant, it is known as a 'change in quantity supplied'. It is graphically expressed as a movement along the same supply curve.

Change in Quantity Supplied — Flowchart

Change in Price

Movement along the Supply Curve

Either

Upward Movement

Expansion in Supply
(due to increase in Price)

Downward Movement

Contraction in Supply
(due to decrease in Price)

Fig 9.4 — Movement along Supply Curve

In Fig 9.4, OQ quantity is supplied at the price of OP.

Upward Movement: when the price rises to OP₁, the quantity supplied also rises to OQ₁ (known as expansion in supply), leading to an upward movement from A to B along the same supply curve SS.

Downward Movement: a fall in price from OP to OP₂ leads to a decrease in quantity supplied from OQ to OQ₂ (known as contraction in supply), resulting in a downward movement from A to C along the same supply curve SS.

Expansion in Supply

Expansion in supply refers to a rise in the quantity supplied due to an increase in the price of the commodity, other factors remaining constant.

It leads to an upward movement along the same supply curve.

It is also known as 'Extension in Supply' or 'Increase in Quantity Supplied'.

Price (in ₹)	Quantity (in units)
20	100
25	150

Fig 9.5 — Expansion in Supply

Quantity supplied rises from 100 units to 150 units, with an increase in price from ₹20 to ₹25, resulting in an upward movement from A to B along the same supply curve SS.

Contraction in Supply

Contraction in supply refers to a fall in the quantity supplied due to a decrease in the price of the commodity, other factors remaining constant.

It leads to a downward movement along the same supply curve.

It is also known as 'Decrease in Quantity Supplied'.

Price (in ₹)	Quantity (in units)
20	100
15	70

Fig 9.6 — Contraction in Supply

Quantity supplied falls from 100 units to 70 units, with a decrease in price from ₹20 to ₹15, resulting in a downward movement from A to B along the same supply curve SS.

Shift in Supply Curve (Change in Supply)

The supply curve illustrates the relationship between price and quantity supplied, assuming all other factors remain constant. However, these other factors are subject to change over time — alterations in these 'other factors' cause the supply curve to shift.

Example: an increase in tax on a commodity will raise its cost of production. With a fall in the profit margin, producers may decrease its supply, even if its market price remains unchanged. Such a decrease in supply, when the price has not changed, cannot be represented by the original supply curve — this results in a shift in the supply curve.

Change in Supply

When the supply of a commodity changes due to a change in any factor other than the commodity's own price, it is known as a 'change in supply'. Graphically, this is expressed as a shift in the supply curve.

Change in Supply — Flowchart

Change in Factors other than Price

Shift in Supply Curve

Either

Rightward Shift

Increase in Supply
(Favorable change)

Leftward Shift

Decrease in Supply
(Unfavorable change)

Change in the price of other goods.

Change in the price of factors of production.

Change in the state of technology.

Change in taxation policy.

Change in objectives of the firm.

Change in the number of firms.

Future expectation of change in price.

Fig 9.7 — Shift in Supply Curve

In Fig 9.7, supply is OQ at the price of OP.

Rightward Shift: when supply rises from OQ to OQ₁ (known as increase in supply) at the same price of OP, it leads to a rightward shift in the supply curve from SS to S₁S₁.

Leftward Shift: a fall in supply from OQ to OQ₂ (known as decrease in supply) at the same price of OP leads to a leftward shift in the supply curve from SS to S₂S₂.

Increase and Decrease in Supply

Increase in Supply

Increase in supply refers to a rise in the supply of a commodity caused due to any factor other than the own price of the commodity. In this case, supply rises at the same price or supply remains the same even at a lower price. It leads to a rightward shift in the supply curve.

Price (in ₹)	Supply (in units)
20	100
20	150

Fig 9.8 — Increase in Supply

Supply rises from 100 units to 150 units at the same price of ₹20, resulting in a rightward shift of the supply curve from SS to S₁S₁.

Decrease in Supply

Decrease in supply refers to a fall in the supply of a commodity caused due to any factor other than the own price of the commodity. In this case, supply falls at the same price or supply remains the same even at a higher price. It leads to a leftward shift in the supply curve.

Price (in ₹)	Supply (in units)
20	100
20	70

Fig 9.9 — Decrease in Supply

Supply falls from 100 units to 70 units at the same price of ₹20, resulting in a leftward shift of the supply curve from SS to S₁S₁.

Movement vs Shift — The Comparisons

Movement along Supply Curve vs Shift in Supply Curve
Aspect	Movement along Supply Curve	Shift in Supply Curve
Meaning	When the quantity supplied changes due to a change in price, keeping other factors constant, it leads to a movement along the supply curve.	When the supply changes due to a change in any factor other than the own price of the commodity, it leads to a shift in the supply curve.
Effect on supply curve	Movement along the same supply curve — either upward (Expansion) or downward (Contraction).	Shift in the supply curve — either rightward (Increase) or leftward (Decrease).
Reason	An increase or decrease in the price of the given commodity.	A change in other factors, like a change in the price of inputs, change in taxes, change in technology, etc.

Change in Quantity Supplied vs Change in Supply
Aspect	Change in Quantity Supplied	Change in Supply
Meaning	When the quantity supplied changes due to a change in price, keeping other factors constant.	When the supply changes due to a change in any factor other than the own price of the commodity.
Effect on supply curve	Movement along the same supply curve — either upward (Expansion) or downward (Contraction).	Shift in the supply curve — either rightward (Increase) or leftward (Decrease).
Reason	An increase or decrease in the price of the given commodity.	A change in other factors, like a change in the price of inputs, change in taxes, change in technology, etc.

Expansion in Supply vs Increase in Supply
Aspect	Expansion in Supply	Increase in Supply
Meaning	When the quantity supplied rises due to an increase in the price, keeping other factors constant.	A rise in the supply of a commodity caused due to any factor other than the own price of the commodity.
Tabular presentation	Price ₹10 → Supply 100 units; Price ₹12 → Supply 150 units.	Price ₹20 → Supply 100 units; Price ₹20 → Supply 150 units (Table 9.6).
Effect on supply curve	Upward movement along the same supply curve.	Rightward shift in the supply curve.
Reason	An increase in the price of the given commodity.	Other factors — decrease in the price of inputs, decrease in taxes, technological upgradation, etc.

Contraction in Supply vs Decrease in Supply
Aspect	Contraction in Supply	Decrease in Supply
Meaning	When the quantity supplied falls due to a decrease in the price, keeping other factors constant.	A fall in the supply of a commodity caused due to any factor other than the own price of the commodity.
Tabular presentation	Price ₹12 → Supply 150 units; Price ₹10 → Supply 100 units.	Price ₹20 → Supply 100 units; Price ₹20 → Supply 70 units (Table 9.7).
Effect on supply curve	Downward movement along the same supply curve.	Leftward shift in the supply curve.
Reason	A decrease in the price of the given commodity.	Other factors — increase in the price of inputs, increase in taxes, technological degradation, etc.

Test Yourself — 6 Scenarios

Price ₹10 → Supply 100 units; Price ₹10 → Supply 140 units.

Price ₹15 → Supply 16 units; Price ₹15 → Supply 12 units.

Price ₹2 → Supply 20 units; Price ₹1 → Supply 15 units.

Price ₹7 → Supply 90 units; Price ₹7 → Supply 60 units.

Price ₹5 → Supply 80 units; Price ₹4 → Supply 65 units.

Price ₹5 → Supply 100 units; Price ₹7 → Supply 120 units.

Effect on Supply Curve due to Changes in Other Factors

The supply curve of a commodity shifts due to a change in any of the factors which were assumed constant under the law of supply.

Select a factor change:

Shift Direction

← Leftward (Decrease)

Production of other goods becomes more profitable. Supply falls from OQ to OQ₁ at the same price OP.

Rightward Shift — Increase in Supply

Decrease in the price of other goods
Decrease in the price of factors of production (inputs)
Advanced and improved technology
Favorable taxation policy (decrease in taxes)
Goal of sales maximization
Increase in the number of firms
Expectation of a fall in prices in the future
Improvement in means of transport and communication

Leftward Shift — Decrease in Supply

Increase in the price of other goods
Increase in the price of factors of production (inputs)
Complex and outdated technology
Unfavorable taxation policy (increase in taxes)
Goal of profit maximization
Decrease in the number of firms
Expectation of a rise in prices in the future
Poor means of transport and communication

Key Takeaways

A change in own price moves the firm along the supply curve: price up → expansion, price down → contraction. ⭐
A change in any other factor shifts the whole curve: favourable changes shift it rightward (increase in supply), unfavourable changes shift it leftward (decrease in supply). ⭐
Movement happens on the same curve; shift happens at the same price — the two must never be confused. ⭐
Input prices fall, technology improves, taxes fall or subsidies rise → rightward shift; the opposites → leftward shift. ⭐
Expansion and contraction are quantity-supplied changes; increase and decrease are supply changes.