You may have heard that light always travels in a straight line. But can you prove it?
- Black cardboard paper.
- Two differently colored LEDs
- Two coin cells (e.g. CR 2450)
- Paper tape
- Scale or any other straight object.
Make a hole in the black cardboard paper
Stick the LEDs to either end of the scale/stick
Place the LEDs in front of the paper
You will need a dark room for this. You will also need to adjust the position of the LEDs till you get the dots on the other side of the paper (just move them back and forth a bit till you get a sharp crisp image of two dots)
See the dots are flipped
Two important things are observed.
- Even though there is one hole, you can still see both dots.
- The dots are flipped.
How does it work?
If we draw the experiment setup on a piece of paper…the answer becomes apparent.
Points to ponder
- Light not only travels straight, it travels in all directions from the source. In this experiment, most of the rays of light are blocked by the opaque paper that does not let light through. The hole makes it easier to observe light by letting in just one “beam” of light in from both sources.
- The yellow light and the red light just passed each other without affecting each other at all. This is quite amazing - photon’s don’t get distracted at all! To me, the mind-blowing part of this experiment is that the yellow light, as it crosses the red light through that tiny hole is not affected at all. The just go through like each other did not exist. That’s exactly why we can see distinct object like a chair, table, or a pen lying on it. The light reflected from these objects do not interfere with other light coming from other objects. How cool is that.
- What happens when you vary the distance of the LEDs from the black cardboard? What happens if you move the black cardboard away from the wall?
Back in the 14th century, a minister in court of King Bukka of the great Vijayanagara kingdom commented on the nature of light, and while he was at it, he laid out the speed at which light travels too. A full 300 years before the official discovery. The calculation is fascinating.