This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
[{'content': 'The focal length of the lens is 0*75 m, what will be its refractive power - \nSelect and explain. \nA. 0.75D, B. 1.5D, C. 1.33 D, D. 1.25 D', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The focal length (f) of a lens is the distance\xa0between the optical centre and the principal focus.\nPower of a lens (P) is defined as the ability of the\xa0lens to converge a beam of light falling on the\xa0lens.\nIt is measured\xa0as reciprocal of the focal length in metres i.e.\xa0P\xa0= 1/f,\xa0The unit of power is dioptre (D). One\xa0dioptre is the power of a lens of focal length one metre.', 'role': 'assistant'}]