$(a)\;\sqrt{\large\frac{T}{\rho}(\large\frac{1}{r}-\large\frac{1}{R})}\qquad(b)\;\sqrt{\large\frac{2T}{\rho}(\large\frac{1}{r}-\large\frac{1}{R})}\qquad(c)\;\sqrt{\large\frac{4T}{\rho}(\large\frac{1}{r}-\large\frac{1}{R})}\qquad(d)\;\sqrt{\large\frac{6T}{\rho}(\large\frac{1}{r}-\large\frac{1}{R})}$