In order to understand about De-Broglie's explanation on Bohr's second postulate,concept of standing waves should be understood. But condition of λ for a given value of length(string) L is given by L=nλ/s where n =1,2,3 etc. But for a string whose ends are connected together and its shape is like a ring and let the radius of ring be r. Then standing waves condition is given by Circumference = nλ/2 2∏r = nλ/2. But this isn't right. it should be 2∏r=nλ I am missing something.Please correct me.