In an atom two electrons move around the nucleus in circular orbits of radii R and 4R. The ratio of the time taken by them to complete one revolution is

Velocity of electron = V cm/s, Circumference = 2πrdistance travelled in one second = VcmVcm.....1 second2πr cm.....?Time taken for one revolution =2πrVWe know r=n2Zr0,V=ZnV1Time taken for one revolution r=2πn2Zr0ZnV1=n3Z22πr0V1                                      =n3Z22×3.14×0.53×10-82.18×108= 1.51 × 10-16 (n3/Z2) secT∝n3Z2Given radius of orbits as R & 4R∵r∝n2Radius of orbit  = R, n = 1Radius of orbit = 4R, n = 2T1 : T2 = 13 : 23= 1 : 8