Q: A real image of a distant object is formed by a plano-convex lens on its principal axis. Spherical aberration is :

\$\textbf{Explanation}\$\$\bullet\$The spherical aberration for a plano-convex lens will be minimum when the curved surface faces the object and then the light from the object will fall on the curved surface. \$\bullet\$This is because the total deviation of the ray is distributed between the two surfaces. Th total deviation is shared by both the surfaces.Hence, the spherical aberration is smaller if the curved surface of the lens faces the object.The correct answer is option (B).

Q: The main reason for axial chromatic aberration in the formation of images by a lens is/are:

Chromatic aberration, also known as “color fringing” or “purple fringing”, is a common optical problem that occurs when a lens is either unable to bring all wavelengths of color to the same focal plane, and/or when wavelengths of color are focused at different positions in the focal plane. Chromatic aberration is caused by lens dispersion, with different colors of light traveling at different speeds while passing through a lens. As a result, the image can look blurred or noticeable colored edges (red, green, blue, yellow, purple, magenta) can appear around objects, especially in high-contrast situations.SO the maain reason is focal length of lens is different for different colors.

Q: The refractive indices of the material of a lens for violet, yellow and red colours of light are respectively \$1.66, 1.64\$ and \$1.62\$. The mean focal length of the lens is \$10 cm\$. Determine the chromatics aberration of the lens between the violet and the red colors.

Let \$\omega\$ be the dispersive power of the material of the lens. Then, the chromatic aberration between violet and red colors is given by:\$f_R-f_V=\omega \times f_Y=(\dfrac{n_V-n_R}{n_Y-1})f_Y=(\dfrac{1.66-1.62}{1.64-1})\times 10=0.625cm\$

Question 1

An achromatic combination of lenses produce :

Accepted Answer

An achromatic combination of lenses provide deviation without dispersion. So, images are unaffected by variation of refractive index with wavelength. Hence correct option is C.

Question 2

A real image of a distant object is formed by a plano-convex lens on its principal axis. Spherical aberration is :

Accepted Answer

$\textbf{Explanation}$$\bullet$The&#10;spherical aberration for a plano-convex lens will be&#10;minimum when the curved surface faces the object and then the light from the object will fall on the curved surface. $\bullet$This is because the total deviation of the ray is distributed between the two surfaces. Th total deviation is shared by both the surfaces.Hence, the spherical aberration is smaller if the curved surface of the lens faces the object.The correct answer is option (B).

Question 3

What causes chromatic aberration?

Accepted Answer

Chromatic aberration occurs when a lens is either unable to bring all wavelengths of color to the same focal plane and/or wavelengths of color are focused at different positions in the focal plane.

Question 4

Which of the following quantities related to a lens depend on the wavelength or wavelengths of incident light?

Accepted Answer

The focal length of the lens varies directly with the wavelength of the light used and as wavelength is inversely related to refractive index, the focal length also varies inversely with it. This is the principal cause of the phenomena of chromatic aberration. The frequency of light has no effect on the focal length.So focal length increases with wavelength but decreases with refractive index and vice versa.And as focal length and power are inversely proportional.Therefore the power, focal length and chromatic aberration of a lens depend on the wavelength or wavelengths of incident light.

Question 5

What is chromatic aberration ? How can it be minimized or eliminated ?

Accepted Answer

The image of a white object (or illuminated by white light) formed by a lens is usually coloured and blurred. This defect of the image produced by a lens is called chromatic aberration. It can be minimized or eliminated by using an achromatic doublet or by achromatic triplet.

Question 6

A thick lens shows more chromatic aberration.

Accepted Answer

Thick lens behave as many thin lenses.

Question 7

The rays of different colours fail to converge at a point after going through a converging lens. This defect is called :

Accepted Answer

By definition, chromatic aberration is the inability of a converging lens to converge rays of different colour at a point after passing through it.

Question 8

The main reason for axial chromatic aberration in the formation of images by a lens is/are:

Accepted Answer

Chromatic aberration, also known as &#8220;color fringing&#8221; or &#8220;purple &#10;fringing&#8221;, is a common optical problem that occurs when a lens is either&#10; unable to bring all wavelengths of color to the same focal plane, &#10;and/or when wavelengths of color are focused at different positions in &#10;the focal plane. Chromatic aberration is caused by lens dispersion, with&#10; different colors of light traveling at different speeds while passing &#10;through a lens. As a result, the image can look blurred or noticeable &#10;colored edges (red, green, blue, yellow, purple, magenta) can appear &#10;around objects, especially in high-contrast situations.SO the maain reason is focal length of lens is different for different colors.

Question 9

The refractive indices of the material of a lens for violet, yellow and red colours of light are respectively $1.66, 1.64$ and $1.62$. The mean focal length of the lens is $10 cm$. Determine the chromatics aberration of the lens between the violet and the red colors.

Accepted Answer

Let $\omega$ be the dispersive power of the material of the lens. Then, the chromatic aberration between violet and red colors is given by:$f_R-f_V=\omega \times f_Y=(\dfrac{n_V-n_R}{n_Y-1})f_Y=(\dfrac{1.66-1.62}{1.64-1})\times 10=0.625cm$

Question 10

A narrow white light beam fails to converge at a point after going through a converging lens. This defect is known as :

Accepted Answer

This defect is known as chromatic aberration. It occurs because the lenses have different refractive indices for different wave lengths of light. Chromatic abberation itself manifests as "fringes" of colour along boundaries that seperate dark and bright parts of the image, because each colour in the optical spectrum can not be focused at a single common point.

Chromatic Aberration

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