Q: The time of revolution of an electron around a nucleus of charge Ze in nth Bohr orbit is directly proportional to

(a) n

(b)n^{3}/Z^{2}

(c) n^{2}/Z

(d) Z/n

Ans: (b)

Sol: $\large T = \frac{2\pi r}{v}$

$ r \propto \frac{n^2}{Z}$ and $ v \propto \frac{Z}{n}$

$ T \propto \frac{n^3}{Z^2}$