Perfect Competition on Long Run

In the long period, the firm reaches the equilibrium in the long period also when its marginal Cost becomes equal to marginal revenue. But in the long period, the firms marginal cost becomes equal to price and the price becomes equal to average cost. If the price is higher than normal profit due to which new firms would enter the industry. Entry of the new firms would increase the supply due to which price would decrease to average cost. In this way, so long even one firm is earning more than normal profit, the new firm would continue so much so profits of all the firms are converted into normal.