According to Snell’s law, the angle of refraction of light passing through a boundary between two media is given by:
n1 sin θ1 = n2 sin θ2
where n1 and n2 are the refractive indices of the media, and θ1 and θ2 are the angles of incidence and refraction, respectively.
For a converging lens, the refractive index of the lens material should be greater than the refractive index of the surrounding medium, while for a diverging lens, the refractive index of the lens material should be less than the refractive index of the surrounding medium.
In this case, the refractive index of the lens material is 1.25, which is less than the refractive index of water (1.33). This means that the light passing through the lens will be refracted away from the normal to the lens surfaces, and the lens will behave as a diverging lens.
To see why this is the case, consider a ray of light passing through the lens. As the light enters the lens from the air (which has a lower refractive index than the lens), it will be refracted towards the normal to the lens surfaces. However, when the light reaches the other surface of the lens, it will be refracted away from the normal since the refractive index of water is higher than the refractive index of the lens. The net effect is that the light is diverged rather than converged by the lens.
Therefore, the biconvex lens made of a transparent material of refractive index 1.25 will behave as a diverging lens when immersed in water of refractive index 1.33.
