Question

Which of the following is/are true about light?
(i) In the ray approximation, light travels in a straight line unless it encounters an obstacle or new medium.
(ii) Light's electric field oscillates in a direction perpendicular to its direction of travel.
(iii) Light's magnetic field oscillates in a direction parallel to its direction of travel.

Please show all work including how you planned for the problem, did the problem, and a potential way to check! Thank you so much!

Answer 1

Solution

i. In the ray approximation, light travels in a straight line unless it encounters an obstacle or a new medium

ii. Lights electric field oscillates in a direction perpendicular to its direction of travel.

These two are the true statements in case of light propagation the other one is false. In the case of first argument, light always travels in a straight line if this is not the case we won't be able to see objects as we see. For the sake of simplicity take a point source emitting light(like a LED light), if light used to travel along curved paths towards our eyes, we will see the point source as situated somewhere else(There will be an apparent shift in objects position). Since this is not the case and we always found objects at their own positions, light must be travelling through direct straight line path unless it is obstacled or enters a new medium.

In the case of second statement, light is a transverse wave i.e, the vibrations in the light wave(the electric and magnetic vibrations) occure in a direction perpendicular to its direction of propagation. The plane wave solution of light propagation can be described by the formula,

Where E is the electric field vector, is its direction and is the propagation vector. It is always true for light that,

That is electric field vibrates in a direction always perpendicular to the propagation direction. The phemophenon of polarization is only shown by transverse wave like light. You cannot observe it in a longitudinal wave like sound. Thus light is indeed a transverse wave