Qstnid -10- What Is The Focal Length Of A Convex Lens Of Focal Length 30 Cm In Contact With A Concave Lens Of Focal Length 20 Cm? Is The System A Converging Or A Diverging Lens? Ignore Thickness Of The Lenses. - 09: Ray Optics And Optical Instruments - Neet-xii-physics

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NEET-XII-Physics

09: Ray Optics And Optical Instruments

II -

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#10
What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.

Ans : Focal length of the convex lens, f₁ = 30 cm

Focal length of the concave lens, f₂ = -20 cm

Focal length of the system of lenses = f

The equivalent focal length of a system of two lenses in contact is given as:

Hence, the focal length of the combination of lenses is 60 cm. The negative sign indicates that the system of lenses acts as a diverging lens.