Q.Explain through a diagram the effect of a rightward shift of both the demand and supply curves on equilibrium price and quantity.

When both the demand and supply curves shift rightward, it signifies an increase in both demand and supply. This situation leads to a definite increase in equilibrium quantity, but the effect on equilibrium price is indeterminate.

Consider an initial equilibrium point $E_0$ where the initial demand curve $D_0$ intersects the initial supply curve $S_0$, determining an equilibrium price $P_0$ and quantity $Q_0$.

1. Effect on Equilibrium Quantity: A rightward shift of the demand curve (from $D_0$ to $D_1$) indicates an increase in demand, which, in isolation, would increase both equilibrium price and quantity. A rightward shift of the supply curve (from $S_0$ to $S_1$) indicates an increase in supply, which, in isolation, would decrease equilibrium price and increase equilibrium quantity. Since both shifts lead to an increase in equilibrium quantity, the new equilibrium quantity $Q_1$ will always be greater than $Q_0$.

2. Effect on Equilibrium Price: The effect on equilibrium price is ambiguous because the demand shift pushes the price up, while the supply shift pushes the price down. The final equilibrium price $P_1$ depends on the relative magnitudes of these shifts:

   • If the increase in demand is greater than the increase in supply, the equilibrium price will rise ($P_1 > P_0$).
   • If the increase in supply is greater than the increase in demand, the equilibrium price will fall ($P_1 < P_0$). …

Understanding the impact of simultaneous shifts in demand and supply requires first recalling what equilibrium means and how individual shifts affect it. Market equilibrium occurs at the intersection of the demand and supply curves, where the quantity demanded equals the quantity supplied, determining the equilibrium price ($P_0$) and equilibrium quantity ($Q_0$).

A rightward shift in the demand curve signifies an increase in demand. At any given price, consumers are now willing and able to purchase more of the good. If supply remained constant, this increased demand would lead to a shortage at the original price, pushing the equilibrium price up and the equilibrium quantity up.

Similarly, a rightward shift in the supply curve signifies an increase in supply. At any given price, producers are now willing and able to offer more of the good for sale. If demand remained constant, this increased supply would lead to a surplus at the original price, pushing the equilibrium price down and the equilibrium quantity up.

Now, let's consider the combined effect of both curves shifting rightward simultaneously.

Diagrammatic Explanation

Imagine an initial market equilibrium where the demand curve $D_0$ intersects the supply curve $S_0$ at point $E_0$, yielding an equilibrium price $P_0$ and equilibrium quantity $Q_0$.

1. Effect on Equilibrium Quantity:

   • An increase in demand (rightward shift of $D_0$ to $D_1$) tends to increase the equilibrium quantity.
   • An increase in supply (rightward shift of $S_0$ to $S_1$) also tends to increase the equilibrium quantity.
   • Since both forces push the quantity in the same direction (upwards), the new equilibrium quantity ($Q_1$) will unambiguously increase compared to the initial quantity ($Q_0$).

2. Effect on Equilibrium Price:

   • An increase in demand (rightward shift of $D_0$ to $D_1$) tends to increase the equilibrium price.

   • An increase in supply (rightward shift of $S_0$ to $S_1$) tends to decrease the equilibrium price.

   • Because these two forces push the price in opposite directions, the net effect on the equilibrium price ($P_1$) is ambiguous. It depends on the relative magnitudes of the shifts. We can illustrate three possible scenarios:

   • Scenario 1: Demand shift is greater than the supply shift.

     If the rightward shift in demand is proportionally larger than the rightward shift in supply, the upward pressure on price from increased demand will outweigh the downward pressure from increased supply. In this case, the new equilibrium price ($P_1$) will be higher than the initial price ($P_0$). The new intersection point $E_1$ will be above and to the right of $E_0$.

   • Scenario 2: Supply shift is greater than the demand shift. …