According to the problem, focal length of objective,
fo=50cm Object distance,
uo=−200cm Image distance,
vo=? Now, from lens formula,
=−⇒=+ ⇒
=+ ∴
vo=cm........(i)
Also, focal length of eyepiece,
fe=5cm,ve=−D=−25cm Again for eyepiece, using lens formula,
=− ⇒
=− Put the given values, we get
=− ∴
ue=−cm .....(ii)
Since, the separation between objective and eyepiece is
L=|vo|+|ue| From eqs. (i) and (ii), we get
L=+ ⇒
L=70.83≃70.8cm