Video Transcript
Which of the following is a correct representation of the path that could be taken by a light ray between points A and B? The light ray does not interact with anything between the two points.
Okay, so here we’ve been given five different options that show us how light rays may possibly travel between points A and B. And the important point that we’ve been told in the question is that the light ray does not interact with anything between the two points. So essentially, we can just imagine the light ray travelling in a vacuum between points A and B.
Now, at this point, we can recall that light rays travel in a straight line from one point to another when travelling through a vacuum. And, in fact, light rays travel through air in a similar way because air has a very minimal effect on the motion of light rays. And because we’ve been told in the question that the light ray does not interact with anything between points A and B, we therefore need to pick the diagram that shows this kind of motion, a straight line between points A and B.
So, looking at option A, first of all, we see that if point A is here and point B is here, the diagram tells us that the light ray first moves to some random point in between A and B that doesn’t fall on the line directly between A and B. And then, the light ray bends and moves back towards B. But if the light rays are not interacting with anything, then what’s causing it to bend, firstly, away from the straight line between A and B and, secondly, back towards B? This means that option A cannot be the answer that we’re looking for.
Moving onto option B then, we see that point A is here and point B is here. The black line, supposedly showing us the motion of the light ray, actually curves from point A to point B. And because we have a curved line here, this is not the straight line that we’re looking for. And hence, option B is not our answer either. Moving on to option C then, we see that point A is here and point B is here. And we also see that the black line shows us a straight line between points A and B, moving from point A to point B. That’s what the little arrow here is showing us. And so, option C seems like a very good candidate for the correct answer to our question. But just to make sure, let’s look at the other two remaining options as well.
Firstly, option D. This one shows a similar sort of thing where there’s a straight line between points A and B that’s been drawn, but it’s got arrows on both ends. In other words, this is somehow suggesting that the light ray travels to the left and to the right, potentially. Whereas what we’re looking for is a straight line from one point to the other. Therefore, option D is not the answer to our question.
Finally, looking at option E, we see that there’s a straight line from point A to some random point between A and B and another straight line from here to B. But there’s no description of what’s happening to the light ray between these two points. It seems like the light ray travels from A to this random point and then just disappears and reappears again at this point before travelling to B. Now, this is not how light travels. There’s nothing to cause the light ray to randomly disappear and reappear again, even if it is along the straight line between A and B.
And hence, option E is not the answer to our question. This means that our initial hunch was right. Option C is indeed the correct answer to our question. The light ray travels in a straight line from point A to point B.
