SATHEE: Optics 3 Question 23

Optics 3 Question 23

23. An eye specialist prescribes spectacles having combination of convex lens of focal length $40 c m$ in contact with a concave lens of focal length $25 c m$ . The power of this lens combination in diopters is

(1997, 2M)

(a) +1.5

(b) -1.5

(d) -6.67

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Answer:

Correct Answer: 23. (b)

Solution:

The focal length of combination is given by

$\begin{aligned} \frac{1}{F} & = \frac{1}{40} - \frac{1}{25} (\frac{1}{F} = \frac{1}{F_{1}} + \frac{1}{F_{2}}) \\ or F & = - \frac{200}{3} c m \\ = - \frac{2}{3} m \end{aligned}$

$∴$ Power of the combination in dioptres,

$\begin{aligned} P & = - \frac{3}{2} & [P = \frac{1}{F (m)}] \\ = - 1.5 \end{aligned}$

Optics 3 Question 23

23. An eye specialist prescribes spectacles having combination of convex lens of focal length $40 c m$ in contact with a concave lens of focal length $25 c m$ . The power of this lens combination in diopters is

Answer:

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Optics 3 Question 23

23. 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

Answer:

Engineering Preparation

Medical Preparation

NCERT Books & Solutions

Important Resources

Other Resources

Syllabus

Test Platform

Sample Mock Test

Mentorship

NCERT Exercise Video Solution

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23. An eye specialist prescribes spectacles having combination of convex lens of focal length $40 c m$ in contact with a concave lens of focal length $25 c m$ . The power of this lens combination in diopters is