Find the focal length of a lens of power negative 2 diopter. So now we know that power is 1 upon the focal length. So negative 2 diopter which is meter inverse is 1 upon the focal length in meter. So the focal length in meters is negative 1 by 2. That is 50 centimeter here. And the negative signifies that this is the con the key way type of lens. And hence our answer is given that the focal length is 50 centimeter. What type of lens it is? It is a concave lens. Thank you.