Movement along the Supply Curve

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When a supply curve is considered, there may be many changes in the curve due to the respective changes in the market prices and other factors effecting the supply of a commodity. One of such changes seen in the supply curve is seen as movement along the supply curve.




Movement along the Supply Curve

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

There can be either a downward movement, i.e. contraction in supply, or an upward movement,i.e. expansion in supply.

Movement along the Supply Curve

In the figure given above, OQ is the quantity supplied at the price OP. Change in price either leads to an upward or a downward movement along the same supply curve –

  1. Upward movement – When price rises to OP1, quantity supplied also rises to OQ1, leading to an upward movement from A to B along the same supply curve SS.
  2. Downward movement – On the other hand, fall in price from OP to OP2, leads to decrease in quantity supplied from OQ to OQ2, resulting in a downward movement from A to C along the same supply curve.

Before we go on to understand other concepts regarding the effects on the supply curve due to various factors, it is important to understand the difference between Change in Quantity Supplied of a commodity and Change in Supply.




Change in Quantity Supplied vs Change in Supply

Whenever supply for the given commodity changes due to change in its own price, then such change in supply is known as ‘Change in Quantity Supplied’. Whereas when  the supply for a commodity changes due to factors other than price, it is known as ‘Change in Supply’.

Expansion in Supply

Expansion in supply refers to a rise in the quantity supplied due to increase in the price of the commodity, other factors remaining constant. It leads to an upward movement along the same supply curve. Extension in supply is also known as ‘Increase in Quantity Supplied’.

Change in Quantity Supplied vs Change in Supply

As seen in the diagram given above, when the price of the commodity rises from Rs. 20 to Rs. 25, the quantity supplied of a commodity increases from 100 to 150 units, 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 decrease in 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’.

Contraction in Supply

As seen in the diagram given above, as the price of the commodity falls from Rs. 100 to Rs. 70, the quantity supplied of the commodity also falls from 100 to 70 units, resulting in a downwards movement from A to B along the same supply curve SS.

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