Change in Demand vs Change in Quantity Demanded: 5 Marks Guaranteed
This is the single most common conceptual error in the first 20 questions of the CA Foundation exam. Do not confuse a 'Movement' with a 'Shift'.
head-to-Head Comparison
| Basis | Change in Quantity Demanded | Change in Demand |
|---|---|---|
| Cause | Change in PRICE of the commodity only | Change in FACTORS OTHER than Price (Income, Taste, etc.) |
| Graphical Representation | Movement ALONG the same curve | SHIFT of the entire curve (Right or Left) |
| Types | Expansion and Contraction | Increase and Decrease |
| Price Status | Price Changes | Price remains Constant |
| Consumer Psychology | Reacting to a deal/discount | Fundamental change in preference or ability to buy |
The 'Graph Interpretation' Trap
If the question says 'The demand curve shifted to the right', asking for the cause, DO NOT select 'Price decreased'. A price decrease causes a downward movement, not a rightward shift. A shift is caused by income, population, or fashion.
Common Ground (Similarities)
- Both result in a change in the amount purchased.
- Both are governed by the Law of Demand (directionally).
Test Your Understanding
Q1: Expansion of supply is caused by:
Improvement in technology
Rise in price of the good ✅
Fall in price of inputs
Government subsidy
Explanation: Expansion is a movement along the curve caused *only* by an increase in the price of the good itself.
Q2: A rightward shift in the demand curve denotes:
Contraction of Demand
Decrease in Demand
Increase in Demand ✅
Expansion of Demand
Explanation: A shift to the right indicates that at the same price, consumers rely want more, which is an 'Increase in Demand'.