The concept of the law of diminishing returns

The law of diminishing returns describes how output changes in the short run when a business increases one factor of production while keeping others fixed. In the short run, not all factors can be adjusted, such as land or capital, which limits how much output can grow.

Key features of the law of diminishing returns

• Short-run application - The law applies only in the short run because at least one factor of production remains fixed, while variable factors like labour can be increased.
• Variable and fixed factors - Variable factors, such as adding more workers, can be changed quickly. Fixed factors, like the number of machines in a factory, cannot be altered in the short term.
• Impact on output - Initially, adding more of a variable factor boosts output efficiently, but eventually, the fixed factors create bottlenecks, reducing the efficiency of further additions.

Statement of the law of diminishing returns

If one variable factor of production is increased while the other factors remain fixed, eventually the marginal returns from the variable factor will start to decrease.

This law is also known as the law of diminishing marginal returns or the law of variable proportions.

How marginal product changes with increased inputs

Marginal product refers to the extra output gained from adding one more unit of a factor of production, such as employing an additional worker. It helps explain how output responds to changes in inputs under the law of diminishing returns.

Changes in marginal product

• Initial increase in marginal product - When a business starts adding more of a variable factor, such as labour, the marginal product often rises. This happens because workers can specialise in tasks, leading to greater efficiency and more output per additional unit.
• Eventual decrease in marginal product - As more units of the variable factor are added, the fixed factors begin to limit productivity. The marginal product starts to fall because resources become overstretched.

Graphical representation of marginal product

A graph of marginal product against factor input typically shows:

• An upward-sloping curve at first, as marginal product increases.
• A peak, followed by a downward-sloping curve as marginal product decreases.
• The horizontal axis represents the factor input (e.g., number of workers), and the vertical axis shows output.

The point of diminishing returns

The point of diminishing returns is a critical stage in production where adding more of a variable factor starts to yield less additional output than before. It marks the transition from increasing efficiency to decreasing efficiency due to fixed factors.

Characteristics of the point of diminishing returns

• Definition - This is the exact level of input where marginal product begins to decline as more units of the variable factor are added.
• Causes - Fixed factors, such as limited machinery or space, restrict the benefits of additional variable inputs.
• Inevitability - The law states that this point is unavoidable in the short run if one factor keeps increasing while others stay fixed.

Examples of diminishing returns in practice

• Manufacturing - A clothing factory with a fixed number of sewing machines will see output rise quickly with the first few machinists, but adding more beyond the number of machines leads to waiting times and lower marginal product.
• Agriculture - On a fixed plot of land, adding more fertiliser initially boosts crop yield, but excessive amounts can harm the soil, reducing the extra yield from each additional application.

The relationship between diminishing returns and marginal cost

Diminishing returns directly affect a business's costs, particularly marginal cost, which is the extra cost of producing one more unit of output. As marginal product changes, so does marginal cost, creating an inverse relationship.

How marginal product influences marginal cost

• Rising marginal product and falling marginal cost - When marginal product increases, each additional unit of output is produced more efficiently, so the marginal cost decreases.
• Falling marginal product and rising marginal cost - As marginal product diminishes, more inputs are needed for each extra unit of output, increasing the marginal cost.
• Mirror image relationship - The marginal cost curve is typically a U-shape, which is the inverse of the inverted U-shape of the marginal product curve. They intersect at the peak of marginal product, where marginal cost is at its lowest.

Graphical representation of marginal product and marginal cost

A combined graph shows:

• The marginal product curve as an inverted U-shape, rising then falling.
• The marginal cost curve as a U-shape, falling then rising, mirroring the marginal product curve.
• This illustrates that diminishing returns lead to higher costs per unit, influencing decisions on production levels.