Q.Suppose the demand and supply curve of commodity X in a perfectly competitive market are given by: $q_D = 700 - p$; $q_S = 500 + 3p$ for $p \ge 15$ and $q_S = 0$ for $0 \le p < 15$. Assume that the market consists of identical firms. Identify the reason behind the market supply of commodity X being zero at any price less than Rs 15. What will be the equilibrium price for this commodity? At equilibrium, what quantity of X will be produced?

Market Equilibrium: Where Buyers and Sellers Agree

Think of a busy vegetable market on a Saturday morning. Sellers have piled up tomatoes, potatoes, and onions. Buyers walk around, inspecting, bargaining. Some sellers price their tomatoes at ₹40 per kg; hardly anyone stops. Another seller keeps them at ₹20 per kg — a crowd forms, and within an hour, her stock is gone.

What you just witnessed is the market searching for a price that works for both sides. That price — where neither a pile of unsold tomatoes remains nor a long queue of disappointed buyers — is the equilibrium price.

The Precise Meaning

Market equilibrium is a state where the quantity that buyers want to buy (demand) exactly equals the quantity that sellers want to sell (supply) at the prevailing price. At this point, there is no tendency for the price to change — unless something outside the market shifts.

This is the only price where the plans of all buyers and all sellers are consistent. No one is forced into an unwanted situation.

Why It Matters

Without equilibrium, markets are unstable. If price is above equilibrium, sellers produce more than buyers want — a surplus (excess supply). Unsold goods pile up, and sellers start cutting prices to clear stock. If price is below equilibrium, buyers want more than sellers produce — a shortage (excess demand). Queues form, and sellers realise they can raise prices.

The market automatically pushes toward equilibrium through price changes. This self-correcting mechanism is what Adam Smith called the "invisible hand." It means that in a free market, resources are allocated without a central planner telling anyone what to do.

A Diagram in Words

Picture a standard graph:

• The demand curve slopes downward (as price falls, quantity demanded rises).
• The supply curve slopes upward (as price rises, quantity supplied rises).
• They cross at one point — the equilibrium point.

Draw a vertical line from that point to the price axis: that's the equilibrium price. Draw a horizontal line to the quantity axis: that's the equilibrium quantity. The two curves meet only once because demand and supply move in opposite directions with price.

What NCERT Says (Class-12, Microeconomics, Chapter 5)

The textbook states clearly:

"Equilibrium price is the price at which the quantity demanded equals the quantity supplied. Equilibrium quantity is the quantity bought and sold at that price."

It also introduces two key terms:

• Excess demand — when $Q_d > Q_s$ at a price below equilibrium. Competition among buyers pushes price up. …