Question

Numerical aperture is expressed as the

(a) NA = sin θa

(b) NA = cos θa

(c) NA = tan θa

(d) NA = sec θa

The question was posed to me in an online interview.

I would like to ask this question from Refractive Index and Numerical Aperture topic in division EM Wave Propagation of Electromagnetic Theory

Answer 1

Right answer is (a) NA = sin θa

Easy explanation: The numerical aperture is the measure of how much light the fiber can collect. It is the sine of the acceptance angle, the angle at which the light must be transmitted in order to get maximum reflection. Thus it is given by NA = sin θa.