<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Joule_heating#Microscopic_description" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Joule_heating#Microscopic_desc...</a><p>Basically, physical movement of electrons involved in the current flow is hindered by other electrons.