(a)\(R_1=\sqrt{n \lambda \tau_0}=\sqrt{(1)(6*10^{-5}cm)(20cm)}=0.0346cm\)

(b)\(R_1=1cm\), \(N=\frac{R_1^2}{\lambda \tau_0}=\frac{1^2}{(6*10^{-5}cm)(20cm)}=833\)

(c)\(f_1=\tau _0=\frac{R_1^2}{N \lambda}=\frac{(0.0346cm)^2}{(1)(6*10^{-5}cm)}=20cm\)

\(f_3=\frac{f_1}{3}=6.67cm\)

\(f_5=\frac{f_1}{5}=4cm\)