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What happens to the focal length of a convex lens when it is immersed in water?
Increases
Decreases
Remains same
Becomes zero
Increases
When a convex lens is immersed in water, its focal length increases. This occurs because the refractive index of water is greater than that of air, which reduces the relative refractive index of the lens material with respect to the surrounding medium.
When a convex lens is immersed in water, its focal length increases. This occurs because the refractive index of water is greater than that of air, which reduces the relative refractive index of the lens material with respect to the surrounding medium.
Think of light refraction like steering a vehicle across different terrains; a smaller difference in resistance between the media results in a gentler bend, shifting the focal point further away.
f1тАЛ=(nMтАЛnLтАЛтАЛтИТ1)(R1тАЛ1тАЛтИТR2тАЛ1тАЛ) тАФ Lens Maker's Formula
According to the Lens Maker's Formula, f1тАЛ=(nMтАЛnLтАЛтАЛтИТ1)(R1тАЛ1тАЛтИТR2тАЛ1тАЛ), the focal length f depends inversely on the term (nMтАЛnLтАЛтАЛтИТ1). As the medium's refractive index nMтАЛ increases from air to water, the ratio nMтАЛnLтАЛтАЛ decreases, which makes the overall value smaller and thus increases the focal length.
Focal length depends on both the refractive index of the lens and the surrounding medium.
Immersing a lens in water decreases its optical power because the focal length increases.
Optical design for aquatic and underwater instruments
Understanding aberrations in fluid-immersed optical systems
Refractive index of glass is typically 1.5, whereas water is approximately 1.33.
If a lens is placed in a medium whose refractive index matches the lens material, its focal length becomes infinite.
A is correct тАФ The focal length of a convex lens increases when it is immersed in water because the relative refractive index decreases.
Always evaluate the surrounding medium's refractive index in optics problems, as a lens can even change its converging/diverging nature if the medium is optically denser than the lens itself.