Question

Find the acceptance angle of a material which has a numerical aperture of 0.707 in air. (a) 30 (b) 60 (c) 45 (d) 90 I got this question in class test. This question is from Refractive Index and Numerical Aperture in division EM Wave Propagation of Electromagnetic Theory Select the correct answer from above options Electromagnetic Theory questions and answers, Electromagnetic Theory questions pdf, Electromagnetic Theory question bank, Electromagnetic Theory questions and answers pdf, mcq on Electromagnetic Theory pdf,electromagnetic theory book pdf,electromagnetic theory pdf notes,electromagnetic theory lecture notes,electromagnetic theory of light,maxwell electromagnetic theory,electromagnetic theory proposed by,electromagnetic theory engineering physics,electromagnetic theory nptel

Answer 1

The correct option is (c) 45 Easy explanation: The numerical aperture is given by NA = n sin θa, where n is the refractive index. It is unity in air. Thus NA = sin θa. To get θ= sin^-1(NA), put NA = 0.707, thus θa = sin^-1(0.707) = 45 degree.