How is 'ucs' calculated in pressure of radiation?

[logearav]

Homework Statement

Revered Members,
While going through pressure of radiation topic in Thermal Physics, i got stumbled at this step.
it has been given P = E/c
If u is the energy density i.e energy per unit volume, then the total energy passing through area 's' of the surface normal to the incident radiation per second = ucs
I don't know how this " ucs " has been arrived.
Please help in this regard. Thanks in advance

Homework Equations

The Attempt at a Solution

 

[edgepflow]

Perform a dimensional analysis as follows:

u (energy / volume) = u (energy / length^3)

u (energy / length^3)
c (length / time)
area(length^2) = energy / time

Multiply this out and see if you can match the expected result.

 

[logearav]

Beautiful sir. Thanks a lot, i got it now