# 3 ways to test that light follows a straight path

Light is an essential part of your day, allowing you to see objects, shapes, and colors. In fact, your pupils filter the light to help you see everything around you. As part of a school assignment, you might be asked to prove that light travels in a straight path. To do this, you can use basic household items in three simple experiments.

## Steps

### Method 1 of 3: Make a pinhole

#### Step 1. Gather the supplies you will need

This experiment will allow you to create a pinhole, which will show you how light travels in a straight line by filtering it through a hole. To make one, you will need the following materials:

• three chips.
• a piece of play dough or putty (you can also use double-sided tape)
• a flashlight or laser pointer
• a piercer
• a rule

#### Step 2. Drill a hole in the center of the tiles

If you want to do this without over-measuring, use the ruler to draw two diagonal lines on a tile connecting opposite corners. Repeat this procedure for the other two tiles.

### Use the hole punch to make a hole in the center of the token where the two lines intersect. Do the same with the other two tiles

#### Step 3. Use the clay to lift the tiles

For this experiment to work, you need to place the tiles in a vertical position, the same distance from each other and in a straight line.

• Form a holder for the cards using the clay so that they are straight and in an upright position. Use the ruler to make sure the tiles are 2 to 5 inches (5.1 to 13.2 cm) apart.
• You can also use double-sided tape to attach the cards to an upright surface. Avoid covering or obstructing the hole in the center of the chips with play dough or tape.

#### Step 4. Place the flashlight or laser pointer at one end of the row of tiles

Hold the flashlight in your hand so that it illuminates the center of the hole on the first tile. Now turn on the flashlight or laser pointer.

### Note that light can be seen through all holes. You should be able to see it through all the holes until you reach a wall or surface beyond the last tile

#### Step 5. Move the flashlight or laser pointer so that it does not illuminate the center of the first chip

You will notice that the light does not pass through the token. This shows that light does not travel in a straight line when it hits a non-reflective material like the token.

### Method 2 of 3: Use a Mirror and Flashlight

#### Step 1. Gather the supplies you will need

This experiment will use the reflection of light from objects to show how light travels in a straight line. You need to do this experiment with someone else, as one person will hold the flashlight and the other the mirror. You will need the following materials:

• two or three sheets of black paper
• a flashlight
• a small mirror
• small objects like buttons, bottle caps, or dimes

#### Step 2. Place the objects on the black paper

Lay the paper on the floor in a dimly lit room or, if possible, in a dark room. Then place two or three small objects in the center of the paper.

#### Step 3. Ask one person to hold the flashlight and another to hold the mirror

The person with the flashlight should sit in front of the objects, with his back to them. For her part, the other will have to hold the small mirror facing the objects.

#### Step 4. Turn on the flashlight

The person will turn on the flashlight so that it shines away from objects.

• The other person will use the small mirror to reflect the light from the flashlight so that it reaches the objects. Bring light in at an angle to catch it so that it hits objects.
• You will probably need to position more than one mirror to create a light path that shines on objects. Try reflecting the light off the mirrors until the light illuminates the objects. You can also move objects around the room to create a more intricate light path using the flashlight as a light source.
• This experiment shows that light travels in a straight line in air. However, it also bounces when it hits a reflective surface, such as a mirror. The angle of the light when it bounces off the mirror will be the same as the angle of the light when it hits it. The mirror reflects light and changes its path from a straight line to a straight line at an angle.

### Method 3 of 3: Use Water and Oil

#### Step 1. Gather the necessary supplies

This experiment will show that light travels in a straight line in air, but will bend when it hits a certain surface, such as water or oil. To perform this experiment, you will need the following materials:

• a large glass jar
• One cup oil
• a rule
• a spoon

#### Step 2. Pour water into the jar

Fill the jar halfway with water.

### Make sure the jar is big enough to fit the ruler

#### Step 3. Use a spoon to pour the oil onto the surface of the water

Pour the oil into the jar so that it forms a solid layer of oil on the surface of the water.

#### Step 4. Place the ruler in the water

Position it so that it is upright in the water and you can see the numbers on the side of the ruler.

• Note that the numbers appear elongated or amplified as the light rays bend in the oil and water. Move the ruler from side to side to observe the different appearances of the numbers in the oil and in the water.
• This will show that light travels at different speeds in different media, such as air, oil, and water. It will travel in a straight line in the air, but will bend when it changes speed due to contact with a certain medium, such as oil or water.