Physics - Geometrical Optics Question with Solution | TestHub

PhysicsGeometrical OpticsRefraction at curved surface/LensEasy2 minPYQ_2020

PhysicsEasysingle choice

It is desired to make a converging achromatic combination of mean focal length $50 cm$ by using two lenses of materials $A$ and $B$ . If the dispersive power of $A$ and $B$ are in ratio $1 : 2,$ the focal lengths of the convex and the concave lenses are respectively

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Answer:

Solution:

$\frac{ω_{1}}{ω_{2}} = \frac{1}{2}$
Now, $\frac{f_{1}}{f_{2}} = - \frac{ω_{1}}{ω_{2}} = - \frac{1}{2}$
Or $f_{2} = - 2 f_{1}$
Now, $\frac{1}{F} = \frac{1}{f_{1}} + \frac{1}{f_{2}}$
$\frac{1}{50} = \frac{1}{f_{1}} + \frac{1}{- 2 f_{1}}$
Or $50 f = \frac{- 2 + 1}{- 2 f_{1}} = \frac{1}{2 f_{1}}$
Or $2 f_{1} = 50$ or $f_{1} = 25 c m$
Again $f_{2} = - 2 \times 25 cm$
$f_{2} = - 50 cm$

Stream:NTA_ABHYAS_NEETSubject:PhysicsTopic:Geometrical OpticsSubtopic:Refraction at curved surface/Lens

⏱ 2mℹ️ Source: PYQ_2020

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