Short run may be defined as a period in which some factors are fixed and some are variable. During short run, it is not possible to increase all the factors of production but only the variable factors can be increased.

The scale of production remains constant in short run. In short run, the output can be increased or decreased only by employing more or less of the variable factors, i.e labour.

It is assumed that in short run the firm doesn't have sufficient time to increase the fixed factors and so the output is dependent only upon the level of the variable factor or we can say the output level can vary only because of the variable factor.

Algebraically, short run production function is expressed as –

Q = f(L, K)

Where –

Q – Output

L- Labour

K – Constant units of Capital

In long run all factors are variable that is all the factors can be changed to increase the output. In long run the scale of production can be changed. In long run a firm can change all its inputs so the output can be increased or decreased by employing more or less of any of the inputs.

It is assumed that in long run the firm have sufficient time to increase the factors of input and so all the factors are variable. In long run “Returns to Scale” phenomenon is in operation.

Algebraically, long run production function is expressed as –

Q = f(L, K)

Where –

Q – Output

L- Labour

K – Capital

Both L & K are variable