It all depends on the CSS for the page. It may not always be purple.
The CSS :visited selector is what controls it:
http://www.w3schools.com/cssref/sel_visited.asp

example:

&lt;style&gt;
    a:visited {color:#00FF00;}   /* visited link */    
&lt;/style&gt;


Why do read links turn purple?
A problem reads "A single phase 50 Hz generator supplies an inductive load of 5000 kW at a power factor of 0.707 lagging ... "
How can there be real power loss from an inductor? 
