when a capitalist wants to expand his or her own capital, he or she must find a solution to extract more surplus value.
the first strategy to do this is to increase the labour. if a worker works for 10 hours in a day, the half of this labour is calculated as the surplus value. For instance, to produce a commodity the work day should only be 5 hours but worker works for 10 ten hours. hence, the supplement 5 hours is considered as the surplus that is extracted by the exploitation of the labour power.
if we want to illustrate it. c=commodity lp=labour power (variable capital) mp=means of production
c= lp + mp
thus capitalist puts money into circulation, and transforms that money into commodity through the production process. M-C
M-C= M+lp+mp
but capitalist circulates the money in production to accumulate more capital. therefore, the money is now a new money. M-C-M'
M'= #M+M that is to say #M represents surplus value. #M=s
s=surplus value which is extracted to force labour power to work more 5 hours in a work day.
however, capitalist wants to increase his or her accumulation, therefore he or she increases the work day hours.
So the new work day hour is, say, 11 hours.
this means that variable capital + constant capital (capitalist's belongings) = 1
but if we increase the hours in work day the surplus value is going to increase as well, this means the rate of exploitation (e) also increases.
that is to say, s is now s'
the value of a commodity is normally represented as c= constant capital + variable capital + surplus value, but it is now constant capital + variable capital + surplus value (+1)