Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
What happens to the focal length of a convex lens if the wavelength of light used is increased?
Increases
Decreases
Remains unchanged
Becomes zero
Increases
When the wavelength of light used with a convex lens is increased, its focal length increases. This occurs because the refractive index of the lens material decreases as the wavelength of light increases, which directly expands the focal length according to the lens maker's formula.
When the wavelength of light used with a convex lens is increased, its focal length increases. This occurs because the refractive index of the lens material decreases as the wavelength of light increases, which directly expands the focal length according to the lens maker's formula.
Think of how a prism disperses light: red light has a longer wavelength and bends less than violet light. Because it bends less, it takes a longer distance to converge, resulting in a larger focal length.
RELAX: Red light (Long wavelength) Always eXpands focal length.
f1тАЛ=(╬╝тИТ1)(R1тАЛ1тАЛтИТR2тАЛ1тАЛ) тАФ Lens Maker's Formula relating focal length to refractive index and radii of curvature
╬╝(╬╗)=A+╬╗2BтАЛ тАФ Cauchy's relation showing the inverse dependence of refractive index on wavelength
The focal length of a lens is governed by the Lens Maker's Formula: f1тАЛ=(╬╝тИТ1)(R1тАЛ1тАЛтИТR2тАЛ1тАЛ). The refractive index ╬╝ depends on the wavelength ╬╗ of light based on Cauchy's relation: ╬╝(╬╗)=A+╬╗2BтАЛ. As the wavelength ╬╗ increases, the refractive index ╬╝ decreases, making the term (╬╝тИТ1) smaller, which results in a larger (increased) focal length f.
Refractive index decreases with an increase in the wavelength of light.
A smaller refractive index leads to weaker bending of light rays, thereby increasing the focal length.
Different colors of light focus at slightly different distances from a single lens, causing chromatic aberration.
Design of achromatic lens combinations to minimize chromatic aberration in cameras and telescopes.
Optical filtering and precise wavelength selection in laser physics.
Blue light has a shorter wavelength and a higher refractive index, meaning it has a shorter focal length compared to red light.
Option B is incorrect because a drop in refractive index reduces the convergence power of the lens, lengthening the focal distance rather than shortening it.
A is correct тАФ The focal length of a convex lens increases when the wavelength of light is increased due to the corresponding decrease in refractive index.
Keep Cauchy's relation in mind for optics questions: wavelength and refractive index are inversely related, which impacts both refraction angles and focal lengths.
Get instant step-by-step AI explanations, full shift Previous Year Papers (SSC GD, RRB, SSC JE), and regional rank analysis on the official Examoogle App.
Free Download тАв 100K+ Aspirants