Light Travels In A Straight Line – Light Path


Light travels in a straight line or curved line, that is a common question for all of us. Many times we all are confused. In this chapter, we discuss all light paths along with proof.

Light Travels in a Straight Line – Introduction

Let’s start an interesting lesson, about Light Path as well as to understand light travels in a straight line. Do you love to ride a bicycle? When you ride your favorite bicycle, you can go on a straight road or you can go on a curved road as well. In the same way, do you know light also travels in a light path?

light travels in straight line basic concept
Fig. 1 Light travels in straight line basic concept

Let us consider, you are in a dark room at day time. How do you make a dark room in a day time, when the sunlight is there! It is very simple! Close all the areas through which light is coming.

Make sure, the following things:

  • All windows are entirely closed.
  • Window curtains are properly covered by the windows.
  • All doors are closed.
  • Electrical Switches for bulb or tube light are switched off. 

Now, no light is coming into the room by any means and the entire room is very dark. 

Now, are you able to see anything?

No, because the light is obstructed to enter into the room. If you open the window slightly, you will see light is coming to the room. Even if, you are opening a very tiny space, a beam of light enters the darkroom.

From these light beams, we are able to see that, light travels in a straight line.

light travels along a straight line - what do you think
Fig. 2 Light travels along a straight line – what do you think?

Understanding Light Path

If you switch on your torch light, in a dusty area, you will see a straight beam of light along with white dust. Light beam means a bunch of light rays for simple understanding.

Refer to the below image for light on a dusty area

You can switched on you light in dusty are to check how does light travels exactly!  

Based on all our examples, it seems light to travel along a straight line.

Now, we will try to understand from a very simple example. Take the following things:

  • A hollow pipe which can be bend
  • A burning candle

We will check the two conditions.

Condition-1: Pipe Is Straight

Let’s lit the candle and take the pipe. Make the pipe straight and see the candle through the pipe. Now, are you able to see it?

Yes!

We are able to see because the light comes to our eyes through the straight pipe. Hence, we can say, the light may go straight to a straight line.

light can travel in straight pipes
Fig. 3 Light can travel in straight pipes

Now, we will make the pipe bend.

Condition-2: Pipe Is Curved

If we bend the pipe. Do you think you can see the candle? 

No! We are not able to see because light can not come to our eyes through this curved pipe. Again, if make the pipe straight, then we can see it again.

light cannot travel in curved pipes
Fig. 4 Light cannot travel in curved pipes

We know, we can see any object, when light ray comes from it and reach our eyes.

  • In the first case, light rays are coming to our eyes through the straight pipe.
  • In the second case, if we bend the pipe, light is not able to come to our eyes.

Hence, it can be said that light can pass through a straight pipe only.

Check out our ANIMATED video!

How To Prove How Light Travels?

Step-1: What to prove

We will prove that light travels in a straight line. 

Step-2: Required Accessories

The path of light can be easily proved by putting an object on its path. We will take a few accessories to prove it. These are:

  • Three cardboards
  • Pins
  • Candle
  • Matchbox
  • Clay
  • Pencil
  • Scale
accessories lights cardboard experiment set
Fig. 5 Accessories lights cardboard experiment set

Step-3: Mark the Middle point

Take these three cardboards and make holes in the middle of each cardboard with the help of a pin. Now, how do you make a hole in the middle of the cardboard? Is it difficult?

No, not at all. It is simple!

  • Take the scale & draw a line between the opposite corners.
  • Draw another line for the rest of the two opposite corners.
  • You will see both these two lines will intersect (crossed) at one point. 
  • This is the middle point of the cardboard. 

Remember finding the middle point is required to make a hole at the same location of all cardboards.

middle of cardboards
Fig. 6 Middle of cardboards

Step-4: Make the holes

Based on the marking of all three cardboards, make the holes with the help of the pin. 

Step-5: Make The Set-Up Ready

All the cardboards should be placed vertically with the help of the clay. Take little clay and fixed it at the base of the cardboard. Make sure, the following three points,

  • All cardboards shall be fixed on a table or a plane surface.
  • Clay shall be placed in such a way that cardboards will not fall.
  • Keep all these cardboards in the same line, as per the picture below.

All the holes shall be in the same line.

cardboards supports clays
Fig. 7 Cardboards supports clays

Step-6: Look The Candle Without Disturbing Cardboards

Now take a candle and place it on one side. make sure, the height of the hole of cardboards and the tip of the candle are the same. And try to look tip of the candle from the opposite side. Are you able to see the tip of the candle now?  Yes, you can see it because the light travels through the holes and reaches your eyes.

all holes are in the same line
Fig. 8 All holes are in the same line

Step-7: Look The Candle After Card Displacement

Now if we displace the cardboard kept in the middle, and observe then we can not see to see the flame of the candle. Why does it happen? Why we are not able to the flame now? Because the light gets blocked by the cardboard.

all holes not same line
Fig. 9 All holes not same line

Step-8: Explain The Results

Since the light could not travel the curved path we can not see the candle. If the light could have traveled a curved path, we could have seen the candle. Now, if we change the cardboard in the previous position so that all the holes are in a straight line, then again we will see the light.

Hence, it is clear that light travels in a straight line only. This is one of the main properties of light and it is most commonly known as rectilinear propagation. 

light travels in straight line proof
Fig. 13 Light travels in straight line proof

Conclusion

To check it clearly, we will draw lines between candle tip, and holes, and eye. We will see this drawn line is in a straight line. Hence, we can say, light travels in a straight line.

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