Question:

A double convex lens made of glass of refractive index $1.56$ has both radii of curvature of magnitude $20 \,cm$. If an object is placed at a distance of $10 \,cm$ from this lens, the position of the image formed is

Updated On: Jul 5, 2022

$22.86$ same side of the object
$22.86$ opposite side of the object
$44.89$ same side of the object
$44.89$ opposite side of the object

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The Correct Option is A

Solution and Explanation

Here, $R_1 = 20 \,cm, R_2 = - 20 \,cm, u = -10\, cm$ and $\mu = 1.56$ Using lens make'rs formula, $\frac{1}{f} = \left(1.56 -1\right)\left(\frac{1}{20}+\frac{1}{20}\right)$ $ \Rightarrow f = \frac{20}{0.56\times2} = 17.86 \,cm $ Now, from lens equation, $v = \frac{uf}{u+f} = \frac{-10\times 17.86}{-10+17.86} = -22.86 \,cm$ Since $v$ is negative, the image will be formed on the same side as that of object.

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Notes on Ray optics and optical instruments

Concepts Used:

Ray Optics and Optical Instruments

Optics, deals with the determination of behaviour and the properties of light, along with its interactions with the matter and also with the instruments that are used to detect it.

Ray optics is also known as the geometrical optics and it is a branch of science which describes light propagation.

Reflection is the change in direction of light at an interface in-between two different media so that the wave-front returns into a medium from which it was originated.

Speed of light is the rate at which the light travels in free space.

A phenomenal change in image formed when the light is passed from one medium to another which is called Refraction.

Total Internal Reflection is the reflection of light when the light ray enters into a rarer medium from a denser medium and the angle of incidence is higher than the critical angle of incidence then that light ray will be reflected back to the denser medium.