Find out the number of waves made by a Bohr electron in one complete revolution in it's $3^{rd}$orbit.

Velocity of the electron in 3rd orbit =3h​/2πmr

where, m= mass of electron and r= radius of 3^rd orbit.

Applying de Broglie equation,

Number of waves =2πr​/λ=2πr/2πr​×3=3.