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NEET-XII-Physics

exam-1 year:2016

with Solutions - page 3
Qstn# 32 Prvs-QstnNext-Qstn
  • #32
    A astronomical telescope has objective and
    eyepiece of focal lengths 40 cm and 4 cm
    respectively. To view an object 200 cm away from
    the objective, the lenses must be separated by a
    distance :-
    (1) 37.3 cm
    (2) 46.0 cm
    (3) 50.0 cm
    (4) 54.0 cm
    digAnsr:   4
    Ans : 4
    Sol. Using lens formula for objective lens
     =
    0 0 0
    1 1 1
    v u f
    &implies; = +
    0 0 0
    1 1 1
    v f u
    &implies; = +
    0
    1 1 1
    v 40 200
    =
    + 5 1
    200
    &implies; v0 = 50 cm
    Tube length  = |v0| + fe = 50 + 4 = 54 cm.