We were meant to do an experiment on optical fibres to see how they work and why but we did not have the time so we were told to use books or the internet to answer few questions.
One of them was: If you point one end of the optical fibre towards a light source and then you cover the end near the light source with something, what will you observe?
Will you still be able to see light coming from the other end of the fibre or will you not be? I personally am very confused lol. I think that you would not able to see any light coming from the fibre because the source of light has been covered with something but at the same time I think that you would be because there is total internal reflection.
What does it mean by cover; wrap it around or put it between the fibre end and light source?
If wrapped around, you would still see light from the source because light travelling down the fibre is reflected and so would never encounter the wrapping.
If as a barrier between the fibre and source you wouldn't see any light because no light passes the covering to enter the fibre. Total internal reflection can only work on light that comes in (and comes in at very close to parallel to the length of the fibre.)
If the obstacle was, say, a coloured filter then you'd see the colour the filter lets through. If it was a diffracion grating then you'd see light if the fibre is in a bright spot of the diffraction pattern.