A lens behaves as a converging lens in air and a diverging lens in water (u = 4/3). What will be the condition on the value of refractive index (u) of the material of the lens ?

If the refractive Index of a lens is less than the refractive index of the medium, it is immersed in , a converging lens will act as a diverging lesns and vice versa .

So if the RI of the converging lens is smaller than the RI of water ie. 4/3, then it will act as a diverging lens.

  • 3
]A lens behaves as a converging lens in air and a diverging lens in water (u = 4/3). It means refractive index of the material of lens is less than the refractive index of water.  
  • -16
Lola
  • -20
The ability of a lens to act as converging or diverging depends upon its refractive index. The refractive index n of the material of a lens depends upon the medium in which the lens is placed. Generally the lens is in air so n gives refractive index of material of lens with respect to air. If you place the convex lens in a medium other than air, then due to change in n, the focal length f of lens changes. if n decreases, f increases. So if you immerse the convex lens in a liquid whose refractive index is greater than refractive index of material of lens then it will change its nature and become concave lens and thus it will start diverging the rays rather than focusing them on a single point. Its true the other way round also that is concave also becomes convex. Hope it helped
  • 14
The condition is that the refractive index of a material of a lens is less than the refractive index of water.
  • 8
water is denser in comparison to the refractive index of lens.
  • 2
As the lens behaves as a converging lens in air its refractive index must be more than that of air i.e 1. Also as it diverges light below water its RI must be less than that of water i.e 1.33. So we can safely tell that the RI of the material of the lens in question falls between 1 - 1.33
  • 7
As the lens behaves as a converging lens in air its refractive index must be more than that of air i.e 1. Also as it diverges light below water its RI must be less than that of water i.e 1.33. So we can safely tell that the RI of the material of the lens in question falls between 1 - 1.33
  • 1
It's an accurate answer Hope it helps

  • 1
What are you looking for?