The refractive index of the material of a concave lens is μ. It is immersed in a medium of refractive index μ1. A parallel beam of light is incident on the lens. The path of the emergent rays when μ1 > μ is:

From the laws of optics, we know that a lens reverses its behaviour when placed in a medium of higher refractive index. Hence, a concave lens diverges light in general, but when placed in a medium of higher refractive index it converges parallel rays of light to a focal point.