2011 iMac heat

[DianeK]

Would someone explain to me why my iMac runs much hotter when I have a thunderbolt display attached? I can't give you exact temperatures, all I can say is without the display, my iMac is never too hot to the touch whereas with the display connected, and running the same applications, sometimes the iMac gets so hot I cannot touch it for more than a few seconds before it becomes too uncomfortable (but never in danger of actually blistering my fingers). The heat is in the upper right corner (oriented facing the screen). And regardless of the temperature, when I listen for the fan at the back it never seems to vary in intensity, i.e very quiet all the time.
Thanks in advance.
Diane

 

[CelestialToys]

The graphics card is doing twice the work so will generate more heat.
The imac getting hot to the touch is normal, this is how it dissipates the heat away from the internal components

 

[DianeK]

Thank you.