Very short answer questions. 1. What is a convex lens? 2. What is the relationship between thickness of lens and focal length? 3. Define the following terms: center of curvature, principal axis, optic focus and focal length. 4. What is focusing? 5. What happens to the ray of light passing through the optical centre of a 6. What is the power of lens? 7. Define one diopter? 3. The magnification of lens is 1, less than 1 and more than 1? What does 2. What is defect of vision? Short answer questions.