This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Elementary Optics, Subject name: Ophthalmology
[{'content': 'What is the power of a lens if the focal length is 0.75 m? \nSelect and explain. \nA. 1.3 D, B. 2.3 D, C. 3.3, D. 4.3 D', 'role': 'user'}, {'content': 'Answer: A \nExplanation: ANSWER: (A) 1.3 DREF: Khurana 4th Ed Pg 23The focal length (f) of a lens is the distance between the optical centre and the principal focus.Power of a lens (P) is defined as the ability of the lens to converge a beam of light falling on the lens. For a converging (convex) lens the power is taken as positive and for a diverging (concave) lens power is taken as negative.It is measured as reciprocal of the focal length in metres i.e. P = 1/f.The unit of power is dioptre (D). One dioptre is the power of a lens of focal length one metre.Hence, substituting in the formula, P=l/0.75 = 1,3 D', 'role': 'assistant'}]