Two thin lenses with focal lengths 25.0 cm and 30.0 cm are placed in contact in
ID: 2097773 • Letter: T
Question
Two thin lenses with focal lengths 25.0 cm and 30.0 cm are placed in contact in an orientation so that their optic axes coincide. What is the focal length of the two in combination? (Hint: A thin lens is one whose thickness is negligible). Answer 13.6 cm 27.5 cm 55.0 cm 150 cm Two thin lenses with focal lengths 25.0 cm and 30.0 cm are placed in contact in an orientation so that their optic axes coincide. What is the focal length of the two in combination? (Hint: A thin lens is one whose thickness is negligible). 13.6 cm 27.5 cm 55.0 cm 150 cm 13.6 cm 27.5 cm 55.0 cm 150 cmExplanation / Answer
SOLUTION:
Focal lenght's of the given lenses,
f1=25 cm , f2=30cm
As these are placed in contact in an orientation so that their
optic axes coincide the distance between them is, x=0 m
It is known by the formula for resultant focal lenght of the
two lens system is,
1/f = 1/f1 + 1/f2 - x/f1f2
1/f = 1/f1 + 1/f2 -( 0 )/f1f2
f=f1f2/f1+f2
=(25 cm )(30 cm )/(25 cm + 30 cm )
=
=13.63 cm
Hence, Answer (1) is correct
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