What will happen to the focal length if the convex lens is dip inside the water.

Focal length of a lens depends on the refractive index of the material of the lens relative to its surrounding medium ....

Hence .. when the lens is placed in water instead of air  .. the focal length increases ..... bcoz the R.I of water is more than R.I of air .....

Hope this helps !!!

 Its focal lenght will decrease because the water has higher refractive index than air!

Hope it helps!!

Please Note--> Focal lenght increases when object is kept at a lower refractive index  while it decreases when it is kept in higher refractive index

 focal length increases

 Really speaking! Lenses depends on a specific property of refraction, which depends on the ratio of refractive indexes of the two media on either side of an interface.
Coming to Focal length of the lens ; the Focal length is inversely proportional to the Refractive index(bending of light) in the medium;
The refractive index ratio of glass(lens) to air is greater than the the refractive index ratio of glass(lens) to water i.e 1.33/1(=1.33) >1.33/1.44 (=0.9236)
So,the focal length increases when it is dipped inside water

But this situation is applicable in convex lens only. It is the opposite in Concave lens

u r telling the opposite ... In concave lens the focal length decreases and in convex lens it increases ....

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