Long run supply curve

The long run supply is a long of time.In the long run even fixed factors can be changed.The firms can enter or leave the industry according to demand condition.If the demand is high,new firm enters the industry and if the demand is low,some firms leave the industry.
In the long run firm will be equilibrium when the MC curve cuts the minimum point of LR average cost curve.The run price will be equal to both marginal cost and minimum average cost.Hence,in the long run the firm produces and sells the indicated by the minimum point of LR average cost curve.
The LR supply curve of industry of LR marginal cost curves due to the following reasons :

1. In the long run only the particular point of LR marginal cost curve is the LR supply curve of a firm not all part of LR marginal cost curve .
2. In the long run,the number of firms change at different prices or demand conditions.
3. In the long run if the industry expands,internal economies and dis economies appear on account of which the LR supply curve of firms shift.Hence,the existing marginal cost cannot be summed up to derive the LR supply curve of industry.

The LR supply curve of a perfect competitive industry will have different shapes depending on whether the industry in facing increasing cost,or decreasing cost or constant cost.