Use the mirror equation to show that an object placed between `f and 2f` of a concave mirror forms an image beyond `2f`.

Explanation

Hydrogen atom
Let r be the radius of the orbit of a hydrogen atom. Forces acting on electron are centrifugal force and electrostatic attraction `(F_(e ))`
At equilibrium.
`F_(c )=F_(e )`
`(mv^(2))/(r )=(1)/(4pi epsilon_(0))(e^(2))/(r^(2))`
According to Bohr’s postulate
`mvr = (nh)/(2pi) rArr u=(nh)/(2pi mr)`
`m((nh)/(2pi mr))^(2)(1)/(r )=(1)/(4pi epsilon_(0))(e^(2))/(r^(2))rArr (mn^(2)h^(2))/(4pi^(2)m^(2)r^(2)r)=(1)/(4pi epsilon_(0))(e^(2))/(r^(2))`
`r=(m^(2)h^(2)epsilon_(0))/(pi me^(2))rArr therefore r alpha n^(2)`