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Komal Sai Aurora
Asked: 2022-11-08T08:05:17+05:30 In:

An eye specialist prescribes spectacles having combination of convex lens of focal length 40cm in contact with a concave lens of focal length 25cm. The power of this lens combination in diopters is
A. `+1.5 D`
B. `-1.5 D`
C. `+6.67 D`
D. `-6.67 D`

An eye specialist prescribes spectacles having combination of convex lens of focal length 40cm in contact with a concave lens of focal length 25cm. The power of this lens combination in diopters is
A. `+1.5 D`
B. `-1.5 D`
C. `+6.67 D`
D. `-6.67 D`
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  1. Correct Answer – B
    Power of the lens combination is
    `P=P_(1)+P_(2)=(1)/(f_(1)(“in m”))+(1)/(f_(2)(“in m”))=(1)/(+0.40″m”)+(1)/(-0.25″m”)`
    ` ” “=-1.5 “m”^(-1)= -1.5 D.`

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Teena Bassi
Asked: 2022-11-04T12:23:11+05:30 In:

An eye specialist prescribes spectacles having combination of convex lens of focal length 40cm in contact with a concave lens of focal length 25cm. The power of this lens combination in diopters is
A. `+ 1.5`
B. `- 1.5`
C. `+ 6.67`
D. `- 6.67`

An eye specialist prescribes spectacles having combination of convex lens of focal length 40cm in contact with a concave lens of focal length 25cm. The power of this lens combination in diopters is
A. `+ 1.5`
B. `- 1.5`
C. `+ 6.67`
D. `- 6.67`
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  1. Correct Answer – b

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Zeenat Mahajan
Asked: 2022-10-30T13:27:55+05:30 In:

An eye specialist prescribes spectacles having combination of convex lens of focal length 40cm in contact with a concave lens of focal length 25cm. The power of this lens combination in diopters is
A. `+1.5 D`
B. `-1.5D`
C. `+6.67`D
D. `-6.67D`

An eye specialist prescribes spectacles having combination of convex lens of focal length 40cm in contact with a concave lens of focal length 25cm. The power of this lens combination in diopters is
A. `+1.5 D`
B. `-1.5D`
C. `+6.67`D
D. `-6.67D`
Parabola
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1 Answer

  1. Correct Answer – B
    (b) `therefore` power of the lens=`1/”Focal length”`
    focal length of combination of convex and cocave lenses is given by
    `1/F=1/(f_(1))=1/F_(2)`
    Where, `f_(1)` and `f_(2)` be the focal lengths of convex and concave lenses, respectively
    Now, `1/F=1/0.4=1/((-0.25))`
    `1/F=-1.5`
    Power, P=-1.5D

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