About plano-convex lens

[kenok1216]

Homework Statement

λ[/B]

Homework Equations

2t=mλ for dark fingers

The Attempt at a Solution

how can i calculate r_{5001 dark},also ,what is the meaning of r in qusetion(r=5mm),<----- it is not the curvature R of plano-convex lens also it is not r_{5001 dark},since it will get incorrect answer so what is radius r mean?

 

[kenok1216]

solved