Sir/ Maam,I want to know why and when do we use the concept of reduced mass. I mean why is it needed in some questions ?Please REPLY SOON !!!!!!!!

Reduced mass is used in two body systems to reduce the system to a single body system with the effective mass as the reduced mass. When considering the Bohr model of hydrogen atom we assume that the mass of the nucleus is very much larger than that of electron so we take the centre of mass of the system to be at the centre of nucleus. To actually the COM of the system is liitle shifted from the cente of nucleus as electron does have some mass. The error in calculations is avoided by using the reduced mass of the electron- nucleus system instead of the mass of the nucleus.