A firm in a perfectly competitive product market takes the price of the product as given. Similarly, a firm in a perfectly competitive factor market takes the price of the factor as given. The firm can hire as much of the input as it wants at the given price. Thus, the supply curve of the input to the firm is a horizontal line at the input price.
Firms seek to maximize their profits. Their decisions regarding how much inputs to hire will be equal to the level that maximizes its profits. Profit maximizing condition for input usage is MRP = MRC. While MRC is the marginal resource cost or the change in total cost due to the employment of an additional unit of an input, MRP is the marginal revenue product or the change in total revenue resulting from the employment of an additional unit of an input. If MRP > MRC then the firm should hire more laborers but it should cut down the labor force if MRP < MRC.
Marginal product (MP) is the change in the quantity of output that results from the employment of an additional unit of an input. Value of marginal product (VMP) is the price of the output multiplied by the marginal physical product of the input. If a firm is a perfect competitor in the product market, MR = P.
Then, MRP = MR . MP
= P . MP
So, for a firm that is a perfect competitor in the product market the profit maximizing condition can be restated as VMP = MRC. If a firm is not perfectly competitive in the product market, then MRP < VMP.
Suppose the firm is also perfectly competitive in the labor market. So the MRC is the same as the price of labor or the market wage (w). The profit maximizing condition can be again re-written as VMP = w.
Once you have thoroughly understood the principles and functioning of the product market, you can easily apply what you have learnt to the factor market. If you face problems or if you have assignments to hand over, contact Expertsmind for their online tutoring or assignment help services.