Problem in calculating young mudulus

[waqarrashid33]

Young moduls can be given as:

Y=(F/A)/(dL/L)
but in area i am confused because sometine for cylindrical shape it is taken as 2(pi)r*L and sometime simply (pi)r^2.
Please deffrientiate these cases:

 

[Doc Al]

If the force is radial, then you need the surface area of the cylinder; if the force is axial, you need the cross-sectional area.