In the previous lesson, we learned about Equilibrium and Demand Forecasting. The theory of production explains how firms convert inputs into outputs. This lesson covers the two fundamental laws of production — the Law of Variable Proportions which applies in the short run, and the Law of Returns to Scale which applies in the long run. Both are frequently tested in CMA Foundation MCQs.
What is Production?
- Production = process of converting raw materials into finished goods for sale in the market
- In economics, only goods made for the market count as production
- Inputs = factors of production used in the process
- Output = goods and services produced
Production Function
Qx = A . f (F1, F2, F3 ……Fn)
| Symbol | Meaning |
|---|---|
| Qx | Quantity of output x |
| A | Efficiency parameter — reflects technology level |
| F1, F2…Fn | Different factor inputs |
- If technology improves → value of A increases → more output from same inputs
Short Run vs Long Run
| Short Run | Long Run | |
|---|---|---|
| Definition | Period where at least one factor is fixed | Period where all factors are variable |
| Fixed factors | Land, building, machines | None — all factors can change |
| Variable factors | Labour, raw materials, capital | All factors |
| Relevant law | Law of Variable Proportions | Law of Returns to Scale |
Law of Variable Proportions (Short Run)
- Also called: Law of Diminishing Marginal Returns
- Developed by Alfred Marshall
- Explains relationship between inputs and output in the short run
- Output is changed by increasing variable factors while keeping fixed factors constant
- Applies to all sectors — agriculture, industry, services
3 Product Concepts:
| Concept | Meaning | Formula |
|---|---|---|
| Total Product (TP) | Total output produced by all units of variable factor | TP = ΣMP |
| Average Product (AP) | Output per unit of variable factor | AP = TP ÷ L |
| Marginal Product (MP) | Additional output from one more unit of variable factor | MP = ΔTP ÷ ΔL |
Table Explanation:
| Units of Labour | Total Product (TP) | Average Product (AP) | Marginal Product (MP) | Stage |
|---|---|---|---|---|
| 1 | 10 | 10 | 10 | I |
| 2 | 22 | 11 | 12 | I |
| 3 | 36 | 12 | 14 | I |
| 4 | 48 | 12 | 12 | I — ends when MP = AP |
| 5 | 55 | 11 | 7 | II |
| 6 | 60 | 10 | 5 | II |
| 7 | 60 | 8.6 | 0 | II — ends when MP = 0 |
| 8 | 56 | 7 | −4 | III |
3 Stages of the Law:
| Stage | TP | AP | MP | Firm operates here? |
|---|---|---|---|---|
| Stage I | Increases | Increases | Increases then falls — MP = AP at end | No — underutilisation |
| Stage II | Increases at diminishing rate | Falls | Falls — reaches 0 at end | Yes — rational zone |
| Stage III | Falls | Falls | Negative | No — irrational zone |
- MP curve cuts AP curve when AP is at its maximum
- A rational producer always operates in Stage II only
Reasons for Diminishing Returns:
- Variable factor units are not homogeneous
- Imperfect substitution between factors
- Factor combination becomes increasingly wrong
Assumptions:
- Variable factor units are homogeneous
- Some factors are fixed, some are variable
- Factor combinations can be changed
- Technology remains constant
- Applicable to short run only
Law of Returns to Scale (Long Run)
- Explains relationship between inputs and output in the long run
- ALL factors of production are changed in the same proportion
- Scale = the combination of all inputs
- Returns = change in output
3 Stages:
| Stage | What happens to output | Example |
|---|---|---|
| Increasing Returns to Scale | Output increases more than proportionately to input increase | Double inputs → more than double output |
| Constant Returns to Scale | Output increases in same proportion as inputs | Double inputs → double output |
| Diminishing Returns to Scale | Output increases less than proportionately to input increase | Double inputs → less than double output |
Table Explanation:
| Scale | Inputs (Land + Labour) | Total Product | Marginal Product | Stage |
|---|---|---|---|---|
| A | 1 + 2 | 4 | — | — |
| B | 2 + 4 | 10 | 6 | Increasing |
| C | 3 + 6 | 18 | 8 | Increasing |
| D | 4 + 8 | 28 | 10 | Increasing |
| E | 5 + 10 | 38 | 10 | Constant |
| F | 6 + 12 | 48 | 10 | Constant |
| G | 7 + 14 | 56 | 8 | Diminishing |
| H | 8 + 16 | 62 | 6 | Diminishing |
| I | 9 + 18 | 66 | 4 | Diminishing |
Causes of Increasing Returns:
- Specialisation and division of labour
- Indivisible factors becoming fully utilised
- Dimensional economies and positive economies of scale
- Volume discounts on inputs
Causes of Diminishing Returns:
- Management problems and diseconomies of scale
- Limits to human coordination
- Lack of cooperation and coordination
- Rise in prices of inputs
Note: Constant returns has no specific cause — it is simply the transition point between increasing and diminishing returns.
Law of Variable Proportions vs Law of Returns to Scale
This comparison is a very common MCQ:
| Law of Variable Proportions | Law of Returns to Scale | |
|---|---|---|
| Time period | Short run | Long run |
| Factors changed | Only variable factors change | All factors change proportionately |
| Factor ratio | Factor ratio changes | Factor ratio stays the same |
| Scale of production | No change in scale | Scale of production changes |
| Example | Land fixed, labour increases | Both land and labour doubled |
Key Concepts to Remember
- Short run = at least one fixed factor; Long run = all factors variable
- Law of Variable Proportions = short run; Law of Returns to Scale = long run
- Rational producer always operates in Stage II of variable proportions
- Stage II = MP falling but positive, TP rising, AP falling
- MP = AP when AP is at maximum
- MP = 0 when TP is at maximum
- MP is negative in Stage III
- Increasing returns to scale → output more than doubles when inputs double
- Constant returns to scale → output exactly doubles when inputs double
- Diminishing returns to scale → output less than doubles when inputs double
- In returns to scale → factor ratio does not change
- In variable proportions → factor ratio changes
Note to Students: These notes are designed for quick revision and MCQ preparation. For detailed explanation with examples, watch our YouTube video lessons. Use these notes alongside practice questions and the full PDF for complete exam preparation.
Free Practice MCQs for Lesson 1.4
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