Measurement of Numerical aperture of optical fibre

1. The value of Numerical aperture of the single mode step index optical fiber is nearly:
2. Diameter of the spot on the screen -------------- as the distance between the outlet of the optical fiber and the screen increases.
3. As the difference between the refractive indices of the core and cladding of Optical fibre increases the Numerical Aperture:
4. If any signal falls on the inlet of the optical fiber at an angle outside the acceptance cone then the signal: