Reflection & Refraction of Light: Physics Lab

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  • 0:01 What Is Reflection &…
  • 0:23 Physics Lab Steps
  • 2:35 Data Analysis
  • 3:46 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

This lesson examines what reflection and refraction are and demonstrates how they work using experimentation. You'll be provided with step-by-step instructions on how to complete the experiments, as well as have the ability to complete a short quiz.

What Is Reflection and Refraction

Reflection is where light bounces off a shiny, reflective surface. Refraction is where light bends when it moves from one medium to another. Light bounces in a particular way, and it bends in a particular way. Today, we're going to investigate reflection and refraction and try to find out how they work using everyday objects.

Physics Lab Steps

For this physics lab, you'll need:

  • A mirror with no border or frame (or not much of one)
  • A piece of paper
  • A pencil and ruler
  • A pin or thumbtack (optional)
  • An aquarium sized tank of water
  • About 300 grams of salt
  • A laser pointer
  • A second large container of water (such as a saucepan)
  • A dark room
  • And, a funnel

Experiment 1: Viewing Reflection

Step 1: Take a sheet of paper, fold it in half and then use the ruler to draw a line along the fold.

Step 2: Stand your mirror on top of the line. Make sure it is straight upright. (You can use document clips or something else that is on hand to hold the mirror steady.) Don't let the mirror move during the lab.

Step 3: Draw a large cross on the paper, in front of the mirror, but towards one side of the paper (meaning not right in the middle). You can then place a thumbtack or pin into the cross to make the experiment a little easier.

Step 4: Turn off the lights, and shine a laser pointer along the surface of the paper, so that it hits the mirror and bounces. Adjust the angle until it hits the cross you drew. To make this easier you can hold your right hand behind the cross, this way you don't have to run it along the paper surface - you can see the laser dot on your hand. Use the pencil and ruler to draw the path of the light, from the laser pointer all the way to the cross.

Step 5: Repeat step 4 from a different position on the paper.

Experiment 2: Reviewing Refraction

Step 1: Fill the aquarium half way with water. Separately, fill the other water container with water and 300 grams of salt. Mix the salt in until dissolved.

Step 2: Use the funnel to pour the saltwater into the bottom of the aquarium. The funnel allows you to make sure the saltwater enters near the bottom.

Step 3: The saltwater should form a layer near the bottom, with less dense fresher water on top.

Step 4: Turn out the lights, and shine the laser pointer through the aquarium at different angles.

Step 5: Note down your observations.

If you haven't already, now it's time to pause the video and get started. Good luck!

Data Analysis

In the first experiment, you investigated reflection. Based on the lines drawn on your paper, you should see clearly that light travels in straight lines. You should also notice that it bounces away from the mirror (reflects) symmetrically. This is called the law of reflection, which says that the incident angle is equal to the reflected angle. These angles are measured from an imaginary line at 90 degrees to the surface of the mirror, called the normal.

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