Supply Revision Notes

Supply refers to the quantity of a good or service that producers are willing and able to sell at different prices over a given period. It is not just about willingness but also the ability to produce and sell the product. For example, a farmer may be willing to sell 100 kilograms of apples at a certain price but can only supply that amount if they have enough apples harvested.

• Supply involves both willingness and ability to sell.
• It is measured over a specific time period.
• Quantity supplied varies with price.

There is a direct relationship between the price of a good and the quantity supplied. Generally, as the price increases, producers are willing to supply more because higher prices can cover higher production costs and increase potential profits. Conversely, if the price falls, producers may supply less because it may not be profitable to produce as much.

For example, if the price of coffee rises from $5 to $7 per kilogram, coffee growers might increase their supply from 1000 kg to 1500 kg.

• Higher prices incentivise producers to supply more.
• Lower prices usually reduce the quantity supplied.
• This relationship is fundamental to the supply curve shape.

While price is a key factor, supply is also influenced by other elements such as production costs, technology, taxes, subsidies, and the number of suppliers in the market. For instance, an improvement in technology can reduce production costs, enabling producers to supply more at the same price.

Example: If a new machine reduces the cost of making shoes, manufacturers may increase supply even if the price remains unchanged.

• Production costs affect supply levels.
• Technological advances can increase supply.
• Government policies like taxes or subsidies impact supply.
• Number of suppliers influences total market supply.

Supply is commonly illustrated using a supply curve on a graph where the horizontal axis (x-axis) shows quantity supplied and the vertical axis (y-axis) shows price. The supply curve typically slopes upwards from left to right, reflecting the positive relationship between price and quantity supplied.

To draw a supply curve, plot points representing different prices and the corresponding quantities producers are willing to supply, then connect these points smoothly or with straight lines.

Example: At $2, quantity supplied might be 50 units; at $4, 100 units; at $6, 150 units. Plotting these points and joining them forms the supply curve.

• X-axis: Quantity supplied.
• Y-axis: Price.
• Upward sloping curve shows direct price-quantity relationship.
• Plot points for different prices and quantities to draw the curve.

The upward slope of the supply curve means that as price rises, quantity supplied increases. Movements along the curve represent changes in quantity supplied due to price changes. For example, moving from a point at $3 to a point at $5 on the curve shows an increase in quantity supplied.

It is important to distinguish between movements along the supply curve (changes in quantity supplied) and shifts of the supply curve (changes in supply due to factors other than price, which is covered in other objectives).

• Movement along the curve = change in quantity supplied due to price change.
• Upward slope reflects positive price-quantity supplied relationship.
• Shifts in supply curve are caused by non-price factors.

Suppliers decide how much of a good to produce based largely on the price they expect to receive. When the price of a product rises, it becomes more profitable to produce and sell, so suppliers are willing to increase the quantity supplied. Conversely, if the price falls, producing the good is less profitable, so suppliers reduce the quantity they offer to the market.

This relationship means that quantity supplied varies directly with price, assuming other factors remain constant. It is important to note that this change in quantity supplied is a movement along the supply curve, not a shift of the curve itself.

• Higher price → higher quantity supplied (extension of supply).
• Lower price → lower quantity supplied (contraction of supply).

A supply curve is a graphical representation of the relationship between price and quantity supplied. It is typically drawn with price on the vertical (y) axis and quantity supplied on the horizontal (x) axis.

The supply curve slopes upwards from left to right, reflecting that higher prices encourage suppliers to offer more goods. Each point on the curve shows the quantity suppliers are willing to supply at a specific price.

For example, if the price of a smartphone is $200, suppliers might be willing to supply 1000 units. If the price rises to $300, the quantity supplied might increase to 1500 units, moving along the curve.

• Price on vertical axis, quantity supplied on horizontal axis.
• Upward sloping curve shows positive price-quantity supplied relationship.
• Movement along the curve indicates change in quantity supplied due to price change.

An extension of supply occurs when a rise in price causes suppliers to increase the quantity supplied. This is represented by a movement up along the supply curve.

A contraction of supply happens when a fall in price leads to a decrease in quantity supplied, shown by a movement down along the supply curve.

It is crucial to distinguish these from shifts in supply, which occur due to factors other than price, such as changes in production costs or technology.

• Extension of supply = increase in quantity supplied due to price rise.
• Contraction of supply = decrease in quantity supplied due to price fall.
• Both are movements along the supply curve, not shifts of the curve.

Consider a farmer selling apples. At a price of $1 per kilogram, the farmer supplies 100 kilograms. If the price rises to $1.50 per kilogram, the farmer is willing to supply 150 kilograms. This increase in quantity supplied from 100 to 150 kilograms is an extension of supply caused by the price rise.

If the price falls back to $0.80 per kilogram, the farmer reduces supply to 70 kilograms, a contraction of supply. These changes are movements along the same supply curve.

• Price increase from $1 to $1.50 → quantity supplied increases from 100kg to 150kg (extension).
• Price decrease from $1 to $0.80 → quantity supplied decreases from 100kg to 70kg (contraction).

Price changes cause movements along the supply curve, affecting the quantity supplied.

An extension of supply is an increase in quantity supplied due to a price rise.

A contraction of supply is a decrease in quantity supplied due to a price fall.

• Price and quantity supplied have a direct relationship.
• Supply curve slopes upwards reflecting this relationship.
• Extension and contraction describe movements along the supply curve caused by price changes.

Individual supply represents the quantity of a good or service that a single producer is willing and able to sell at various prices over a given period. This quantity depends on factors such as production costs, technology, and the producer's capacity. For example, a farmer may supply 100 kilograms of apples at $2 per kilogram but increase supply to 150 kilograms if the price rises to $3 per kilogram. This relationship between price and quantity supplied by one producer is illustrated by the individual supply curve, which typically slopes upwards, reflecting that higher prices incentivise greater supply.

• Individual supply is specific to one producer.
• Quantity supplied varies with price changes.
• Influenced by production costs and technology.

Market supply is the total quantity of a good or service that all producers in a market are willing and able to sell at different prices. It aggregates the individual supplies of every producer offering that good or service. For instance, if three farmers supply apples, their individual quantities at a given price add up to the market supply at that price. The market supply curve is therefore derived by horizontally summing the individual supply curves of all producers in the market.

• Market supply sums all individual supplies.
• Reflects total quantity available at each price.
• Forms the market supply curve by aggregation.

To find the market supply at a particular price, add the quantities supplied by all individual producers at that price. For example, if Producer A supplies 100 units at $5, Producer B supplies 150 units, and Producer C supplies 50 units, the market supply at $5 is 100 + 150 + 50 = 300 units. Repeating this for various prices produces the market supply curve. This process is called horizontal summation because quantities are added along the quantity axis for each price point.

• Add quantities supplied by all producers at each price.
• Horizontal summation creates market supply curve.
• Example: 100 + 150 + 50 units = 300 units market supply.

Changes in factors such as production costs, technology, taxes, or the number of suppliers affect individual supply. For example, if a new technology reduces production costs for a producer, they can supply more at each price, shifting their individual supply curve to the right. When many producers experience similar changes, the market supply curve shifts accordingly. An increase in the number of suppliers also increases market supply, shifting the curve rightwards. Conversely, higher production costs or fewer suppliers shift supply curves leftwards, reducing quantities supplied at each price.

• Production costs and technology affect supply.
• Number of suppliers influences market supply.
• Shifts in individual supply curves aggregate to market supply shifts.

Understanding how individual supplies combine helps explain market behaviour. For example, if prices rise, individual producers increase supply, raising market supply. If some producers exit the market, total supply decreases even if prices remain constant. This knowledge aids in predicting how market supply responds to economic changes and policy decisions. For instance, a subsidy to producers may lower costs, increasing individual and market supply.

• Price changes influence individual and market supply quantities.
• Producer entry or exit affects market supply levels.
• Policy changes can shift supply curves by altering costs.

The supply curve shows the relationship between the price of a good (vertical axis) and the quantity supplied (horizontal axis). It slopes upwards because higher prices incentivise producers to supply more.

A change in price causes a movement along the supply curve: an extension (increase in quantity supplied) if price rises, or a contraction (decrease in quantity supplied) if price falls.

A shift of the supply curve means that at every price, the quantity supplied changes. A rightward shift indicates an increase in supply, while a leftward shift indicates a decrease in supply. These shifts are caused by factors other than price, known as non-price determinants of supply.

• Price on vertical axis, quantity supplied on horizontal axis.
• Movement along curve = change in quantity supplied due to price change.
• Shift of curve = change in supply due to non-price factors.

Production costs include expenses for raw materials, wages, energy, and rent. If production costs fall, it becomes cheaper to produce goods, so suppliers are willing to supply more at every price, shifting the supply curve right (increase in supply).

Conversely, if production costs rise, supply decreases and the curve shifts left.

For example, a fall in the price of steel reduces costs for car manufacturers, increasing supply of cars.

• Lower costs → supply increases (curve shifts right).
• Higher costs → supply decreases (curve shifts left).

Improvements in technology can make production more efficient, reducing costs or increasing output from the same inputs.

This leads to an increase in supply, shifting the supply curve to the right.

For instance, automation in factories can speed up production, increasing the quantity supplied at all prices.

• Better technology → supply increases (right shift).
• Worse or outdated technology → supply decreases (left shift).

Taxes on production increase costs, causing supply to decrease and the curve to shift left.

Subsidies reduce costs for producers, increasing supply and shifting the curve right.

Regulations can either increase costs (reducing supply) or improve production conditions (potentially increasing supply). For example, stricter environmental laws may raise costs and reduce supply.

• Taxes ↑ → supply ↓ (left shift).
• Subsidies ↑ → supply ↑ (right shift).
• Regulations impact supply depending on their nature.

An increase in the number of suppliers in a market increases total market supply, shifting the supply curve right.

If suppliers expect future prices to rise, they might withhold supply now, decreasing current supply and shifting the curve left.

For example, if farmers expect higher crop prices next season, they may store produce, reducing current supply.

• More suppliers → supply increases (right shift).
• Fewer suppliers → supply decreases (left shift).
• Expectations of future prices affect current supply decisions.