In a competitive factor market,a firm can buy any amount of the input it wants without affecting the price. Therefore the firm faces a perfectly elastic supply curve for that input. As a result,the quantity of the input purchased by the producer of the product is determined by the intersection of the input demand and supply curves. In a competitive factor market, a firm can buy any amount of the input it wants without affecting the price. Therefore the firm faces a perfectly elastic supply curve for that input. As a result, the quantity of the input purchased by the producer of the product is determined by the intersection of the input demand and supply curves