Explain Law of variable prorotion

The Law of Variable Proportion explains how the output changes when one factor of production is made variable keeping other factors constant. In other words, it refers to the input-output relation when output is increased by varying the quantity of one input.In this law, the unit of labour change by keeping capital constant . As a number of fixed factors,capital is fixed then fixed factor and variable factor can be combined together in varying proportion. So, it is also called " The Law of Proportionality".
If we increase the quantity of variable factor keeping a number of fixed factors constant, then the total production initially increase at increasing rate, then the increase at decreasing rate becomes minimum and ultimately, the total production begins to fall. This law is also called "Short Run Production Function". The short run production function can be expressed as:
Q = f(K, L)

Where, Q = Output

L = Variable input labour

K = Fixed input capital