Physics - Geometrical Optics Question with Solution | TestHub

PhysicsGeometrical OpticsRefraction at curved surface/LensEasy2 minPYQ_2020

PhysicsEasysingle choice

Two lenses of power $+ 10 D$ and $- 5 D$ are placed in contact. Where should an object be held from the lens, so as to obtain a virtual image of magnification $2$ ?

Options:

Answer:

Solution:

Here, $P_{1} = + 10 D, P_{2} = - 5 D$

Combined power,

$P = P_{1} + P_{2} = 10 D - 5 D$

$P = 5 D$

$∴$ Combined focal length

$= \frac{1}{P} m = \frac{100}{P} cm = \frac{100}{5} = 20 cm$

Given magnification,

$m = 2$

$\frac{v}{u} = 2$

$v = 2 u$

By lens formula,

$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

$\frac{1}{2 u} - \frac{1}{u} = \frac{1}{20}$

$\frac{1 - 2}{2 u} = \frac{1}{20}$

$2 u = 20$

$u = - 10 cm$

Hence, to obtain virtual image, object should be place at a distance of $10 cm.$

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

⏱ 2mℹ️ Source: PYQ_2020

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