Find the frequency of revolution of an electron in Bohr's 2nd orbit; if the radius and speed of electron in that orbit is 2.14×10^(−10) m and 1.09×10^6m/s respectively.

The energies of the electron in the second and the third Bohr orbits of the hydrogen atoms are -5.42xx10^(19)J and -2.41xx10^(19)J respectively. Calculate the wavelength (in S.I. unit) of the emitted radiation, when the electron jumps from the third to the second orbit.

The frequency of horn of a car drops by 10% as the car passes a stationary observer.What is the speed of the car?[velocity of sound = 330 m/s]

Find the surface area of a cylinder whose- Radius of the base is 7m and height 10m.

The radius of the inner most electron orbit of a hydrogen atom is 5.3xx10^(-11) m. Find out the radii of the n=2 and n= 3 orbits?