Rise of Digital Payments
The question
In the economy of Novara, mobile and card-based payment apps are adopted almost universally, letting households and firms complete purchases while holding far less currency and far smaller checking balances at every interest rate. Show the effect of this change on the money market, assuming the price level, real income, and central bank policy are all unchanged. Show the effect on the Money Market graph.
Drag a curve, or use the arrow buttons. Want the free-play version with every control? Open this graph in the sandbox.
Rise of Digital Payments: the worked answer
On the Money Market graph, Money demand (MD) shifts left.
Why Money demand (MD) shifts left
The new payment technology lets people carry out the same transactions while holding less money, so the quantity of money desired at every interest rate falls. This is a decrease in money demand, so the MD curve shifts to the left. Because the price level, real income, and central bank policy are all unchanged, nothing alters the fixed quantity of money supplied, so the vertical MS line stays put.
What happens to the equilibrium
The equilibrium nominal interest rate falls while the quantity of money is unchanged.
The mistake students make on this one
The typical wrong answer is shifting MS left, on the reasoning that "people are holding less money, so there is less money." The quantity of money in existence has not changed by a single dollar; only the amount people wish to hold at each interest rate has fallen, and the rate drops until they are willing to hold the same fixed quantity.
On exam day
Any innovation that lets people make the same purchases with smaller money balances, such as credit cards, ATMs, or payment apps, shifts MD left and leaves MS exactly where it was.
How this is graded
The checker reads every curve's position before and after your answer. You are marked correct only when Money demand (MD) shifts left and every other curve on the Money Market graph stays where it started — the same standard an AP reader applies to a drawn graph: the right shift, and nothing extra. There is no AI involved; the rubric is the geometry.
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