NEET Physics Question - Ray Optics - Lens Makers Formula/ Len's Formula

Assertion (A): The Focal length of lens is same for all colours of light

Reason (R): The focal length depends only upon the material of the lens

Both (A) & (R) are true and the (R) is the correct explanation of the (A)

Both (A) & (R) are true but the (R) is not the correct explanation of the (A)

(A) is true but (R) is false

Both (A) and (R) are false

Solution:

The focal length of a lens is given by \(1/f = (n-1)(1/R_1 - 1/R_2)\). Since the refractive index \(n\) varies with the color of light, focal length is different for different colors. Thus (A) is false. Focal length depends on \(n\), \(R_1\), \(R_2\), and the surrounding medium, not only the material. Also, \(n\) for a material depends on color. So (R) is false. Both (A) and (R) are false.

Rankers Physics

Focal Length and Color

Solution:

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