The supply of labor is the quantity of labor workers are willing and able to provide at each wage rate, and it is positively related to the wage (EK PRD-4.A.2). In AP Micro Unit 5, it determines the market wage in competitive labor markets and the marginal factor cost in monopsony markets.
The supply of labor is the relationship between the wage rate and the quantity of labor workers offer. Higher wages pull more people into the market and convince existing workers to work more hours, so the labor supply curve slopes upward. That's the core of EK PRD-4.A.2, and it's the mirror image of labor demand, which slopes downward.
Here's the part that actually decides exam questions. The market supply curve always slopes upward, but the supply curve a single firm faces depends on the market structure. In a perfectly competitive labor market, one firm is too small to affect the wage, so it sees a horizontal (perfectly elastic) supply curve at the market wage. In a monopsony, the firm IS the market, so it faces the entire upward-sloping supply curve. To hire one more worker, it has to raise the wage for everyone, which is why marginal factor cost sits above the supply curve. Same concept, two completely different graphs.
Supply of labor lives in Unit 5 (Factor Markets) and runs through Topics 5.1, 5.3, and 5.4. It directly supports AP Micro 5.1.A (defining factor market concepts with graphs), AP Micro 5.3.A and 5.3.B (perfectly competitive labor markets, where supply and demand together set the market wage that becomes the firm's MFC), and AP Micro 5.4.A and 5.4.B (monopsony, where the upward-sloping supply curve the firm faces drives a wedge between wage and MFC). The enduring understanding behind all of it is PRD-4. Factor prices like wages provide incentives, and the supply of labor is exactly how workers respond to those incentives. If you can't draw labor supply correctly in both market structures, the entire Unit 5 graph toolkit falls apart.
Keep studying AP Microeconomics Unit 5
Demand for labor (Unit 5)
Labor supply is one half of the labor market graph, and labor demand is the other. Demand for labor is derived demand, coming from the firm's marginal revenue product. Where the two curves cross, you get the equilibrium wage and employment level for the whole market.
Monopsony and marginal factor cost (Unit 5)
In monopsony, the supply curve doubles as the wage the firm must pay at each hiring level, while MFC rises faster above it. The firm hires where MRP = MFC but pays the lower wage off the supply curve. That gap is why monopsonies hire fewer workers and pay less than competitive markets.
Wage rate (Unit 5)
The wage rate is the price on the labor supply graph's vertical axis. Movements along the supply curve come from wage changes, while shifts come from things like population, preferences, or alternatives. Confusing a movement with a shift is a classic MCQ trap carried over from Unit 2 supply logic.
Price floors and minimum wage (Units 2 and 5)
A minimum wage set above equilibrium works exactly like a price floor from Unit 2, but in the labor market. Quantity of labor supplied rises, quantity demanded falls, and the gap is unemployment. The twist comes in monopsony, where a well-placed minimum wage can actually increase employment.
Supply of labor shows up mostly in MCQs and in the Unit 5 graphing FRQ. Expect questions like these. First, the basic law of supply applied to labor, such as predicting that a wage increase raises quantity of labor supplied along an upward-sloping curve. Second, shift questions, like what happens to wages and employment when new firms enter a competitive labor market and demand for labor shifts right along the supply curve. Third, minimum wage analysis, where a binding wage floor above equilibrium creates a surplus of labor (unemployment). Fourth, monopsony graphs, where you must draw the upward-sloping supply curve, place MFC above it, hire where MRP = MFC, and then drop down to the supply curve to find the wage. A common scenario asks what happens when a monopsonist suddenly faces competition for workers, and the answer hinges on the firm losing its wage-setting power. Drawing supply correctly is the difference between earning and losing those graph points.
In a monopsony, the supply curve and the MFC curve are two different lines, and mixing them up wrecks the graph. The supply curve shows the wage needed to attract each quantity of workers. MFC shows the cost of hiring one more worker, which includes that worker's wage PLUS the raise you now owe every existing worker. So MFC rises faster and sits above supply. In a perfectly competitive labor market they collapse into the same horizontal line, because the firm pays the market wage no matter how many workers it hires. That's the structural difference the exam tests over and over.
The quantity of labor supplied is positively related to the wage rate, so the market labor supply curve slopes upward (EK PRD-4.A.2).
In a perfectly competitive labor market, an individual firm faces a horizontal labor supply curve at the market wage, so wage equals marginal factor cost.
In a monopsony, the firm faces the upward-sloping market supply curve, which pushes MFC above the supply curve and makes the wage paid lower than MRP at the profit-maximizing quantity.
A minimum wage set above the equilibrium wage increases quantity of labor supplied, decreases quantity demanded, and creates unemployment in a competitive labor market.
Shifts in labor supply come from non-wage factors like population, preferences, and alternatives, while a wage change only moves you along the existing curve.
To find the monopsony wage on a graph, hire where MRP = MFC, then read the wage off the supply curve directly below that quantity.
It's the quantity of labor workers are willing and able to provide at each wage rate. Higher wages mean more labor supplied, so the curve slopes upward, which is the labor-market version of the law of supply tested in Unit 5.
No, not always. The market curve always slopes upward, but a firm in a perfectly competitive labor market faces a horizontal supply curve at the market wage because it's too small to affect wages. Only a monopsonist faces the full upward-sloping market curve.
Supply comes from workers deciding how much to work at each wage and slopes upward. Demand comes from firms and is derived from the marginal revenue product of labor, so it slopes downward. Households supply labor and firms demand it, which is the reverse of product markets.
Because hiring one more worker means raising the wage for all existing workers too. The supply curve only shows the new worker's wage, but MFC adds in those raises, so MFC is greater than the supply price at every quantity beyond the first (EK PRD-4.D.2).
Not always. In a competitive labor market, a minimum wage above equilibrium creates a surplus of workers, meaning unemployment. But in a monopsony, a minimum wage set between the monopsony wage and the competitive wage can actually raise both the wage and employment.