Exactly, 24mm is 24mm. Both lenses, a fictional EF-S 24 and a EF 24 would project same sized images on the sensor plane. The difference is, of the EF-S lens only the center part would be usable, the corners would be very dark and not sharp. If you mount a lens designed for crop cameras on a full frame camera (some third party lenses let you do that), you will see it.
Since a crop camera uses only uses the center part, you usually never see that.
So why do EF-S lenses exist? They can be built lighter and smaller than a lens of the same focal length for full frame.

Hope that helps.
Btw where are you from?

Arnt