Physics - Geometrical Optics Question with Solution | TestHub

PhysicsGeometrical OpticsRefraction at curved surface/LensEasy2 minPYQ_2020

PhysicsEasysingle choice

An illuminated object and a screen are placed $90 cm$ apart. The focal length and nature of the lens required to produce a clear image on the screen, twice the size of the object would be:

Options:

Answer:

Solution:

$∴ u + v = 90$ ...(i) $m = \frac{υ}{u} \Rightarrow 2 = \frac{υ}{u} \Rightarrow v = 2 u$ ...(ii)Putting the value of v in (i), we get $u + 2 u = 90 \Rightarrow u = \frac{90}{30} = 30$ $∴ v = 2 \times 30 = 60$ Using lens formula, we get $\begin{array}{l} \frac{1}{f} = \frac{1}{υ} - \frac{1}{u} \\ \Rightarrow \frac{1}{f} = \frac{1}{60} - \frac{1}{- 30} \\ \Rightarrow \frac{1}{f} = \frac{1}{60} + \frac{1}{30} \\ \Rightarrow \frac{1}{f} = \frac{1 + 2}{60} = \frac{3}{60} \\ \Rightarrow f = \frac{60}{3} ∴ f = 20 cm . \end{array}$

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

⏱ 2mℹ️ Source: PYQ_2020

Doubts & Discussion

Loading discussions...