SATHEE: Optics Question 822

Optics Question 822

Question: An eye specialist prescribes spectacles having combination of convex lens of focal length 40 cm in contact with a concave lens of focal length 25 cm. The power of this lens combination in diopters is

Options:

A) +1.5

B) -1.5

C) +6.67

D) -6.67

Show Answer

Answer:

Correct Answer: B

Solution:

[b] $f_{1} = + 40 c m = 0.4 m$ (for convex lens) $f_{2} = - 25 c m = - 0.25 m$ (for concave lens)

$∴$ Focal length (f) of the combination $\frac{1}{f} = \frac{1}{f_{1}} + \frac{1}{f_{2}} = \frac{1}{0.40} - \frac{1}{0.25} = \frac{0.25 - 0.4}{0.40 \times 0.25}$

$= - \frac{0.15}{0.1} = - 1.5 dioptre . \Rightarrow P= \frac{1}{f} = - 1.5 dioptre$

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Optics Question 822

Question: An eye specialist prescribes spectacles having combination of convex lens of focal length 40 cm in contact with a concave lens of focal length 25 cm. The power of this lens combination in diopters is

Options:

Answer:

Solution:

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