Reflection, Refraction, Diffraction


Reflection, Refraction, Diffraction introduces students to these three properties of light. Students will discover how light behaves differently when it encounters different kinds of objects. If it reaches a very smooth object, it reflects. If it passes through one medium to another, it refracts. And sometimes, it bends around an obstacle in its path, or diffracts.

There are a few different suggestions or alternatives that you can use listed in the “Options for Lesson” section. For instance, you could obtain a laser pointer or flashlight and a glass of water to use as an object lesson to illustrate how light behaves under unique circumstances.

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What our Reflection, Refraction, Diffraction lesson plan includes

Lesson Objectives and Overview: Reflection, Refraction, Diffraction teaches students about how light reacts in different settings. While students may be familiar with reflection and refraction, diffraction might be a new concept to them. Students will be able to define each of these three terms and explain their meaning. They will also be able to describe the traits of these three properties of light. This lesson is for students in 4th grade, 5th grade, and 6th grade.

Classroom Procedure

Every lesson plan provides you with a classroom procedure page that outlines a step-by-step guide to follow. You do not have to follow the guide exactly. The guide helps you organize the lesson and details when to hand out worksheets. It also lists information in the yellow box that you might find useful. You will find the lesson objectives, state standards, and number of class sessions the lesson should take to complete in this area. In addition, it describes the supplies you will need as well as what and how you need to prepare beforehand.

Options for Lesson

There are a number of suggestions in the “Options for Lesson” section that you can take advantage of if you have time or want to extend the lesson further. One idea is to plan an additional activity in which students use a number of objects (e.g., laser pointer, flashlight, glass of water, mirror, etc.) to demonstrate and explain the three properties of light. Hands-on activities help students better understand the concepts they learn about. Another idea is to assign students one of the three properties to study and research. Students can then present a more detailed report about that particular property.

Teacher Notes

The paragraph on this page provides a little extra guidance or instruction as you prepare the lesson. It suggests using this lesson in conjunction with others that relate to light or physical science in general. You can use the blank lines to write down any other ideas you have before giving the lesson to students.



The Reflection, Refraction, Diffraction lesson plan contains four pages of content. The first page provides students with background information on light. Students will learn that light is a form of energy that becomes visible when it reflects off the surface of an object.

Light travels at a speed of 186,000 miles per second, so it actually takes eight minutes for light from the sun to reach the earth. Nothing in the universe can travel faster than light. It can also travel through liquids and gases, as well as some solids if they are transparent or translucent, such as glass.

Light easily passes through transparent objects, like clear water or glass. Translucent objects scatter light waves in different directions. Opaque objects, however, such as a tree or a person, do not allow light to pass through. There are several ways light can be controlled or changed: reflection, refraction, or diffraction.


The first way to change or control light is through reflection. In physics, reflection occurs when a light wave encounters an object that acts as a barrier, or reflects or bounces off a surface. This causes the light wave to return to the original medium. This is how mirrors allow people to see themselves reflected on their smooth surfaces.

Light can reflect off any surface at different angles, and the angle of the reflection depends on the angle at which the light hits the object’s surface. Light waves travel in straight lines, so the angle of reflected light on a smooth surface will be the same angle at which the light wave hit the surface initially. The lesson provides a small object lesson using a small light or laser and a mirror to demonstrate this concept.

Euclid, in 300 BC, was the first person to scientifically study the concept of reflection. He discovered that when light hits an object, the object will absorb certain wavelengths of the light and reflect others. The wavelengths it absorbs or reflects depend on the chemical and physical composition of the object. The lightwaves that reflect off the object determine the color of that object.


The second way light changes is through refraction. Refraction happens when a light wave changes direction upon moving from one medium to another with a different density. The angle of the original light wave and the angle of the refracted wave are different. For instance, when someone puts a pencil in a glass of water, the pencil no longer looks the same. This is because the different densities of the mediums of air and water in a glass cause the light waves to refract in different angles.

Students will learn at this point about the concept of prisms and how they refract light. As white light enters a prism, the different wavelengths do not refract in the same way. Instead, each wavelength separates into the colors of the rainbow and appears at a different angle. As another example, stars appear to twinkle due to the refraction of their light by the earth’s atmosphere.

The first person to study refraction was a Roman scientist named Ptolemy in the 2nd century. He discovered that the angle of the original light wave was proportional to the angle of refraction. Later, a mathematician developed an equation to represent this concept.


The final way to change or control light is through diffraction. This occurs when a light wave stays in the same medium but bends around an obstacle. This aspect about light led scientists to conclude that light had wave-like properties and consist of a linear stream of particles. Italian physicist Francesco Grimaldi was the first to use the term diffraction to describe this property.

Grimaldi described an occasion when a single beam of light traveled through a narrow slit. The light split into different directions and created an interference pattern. In other words, lightwaves can bend or go around an object. This phenomenon makes light waves similar to water waves that hit a boat and bend around the boat.

Similarly, students will discover that water waves and sound waves can travel around corners, around objects, and through openings. The lesson provides a diagram to illustrate how light diffracts when passing through a slit or when encountering a barrier. Light waves display the same ability as sound and water waves. The interference occurs due to the diffraction of light around the sides of the object. The waves break into different wavelengths once the light passes through the slit in the first picture and goes around the coin in the second picture.

Key Terms

Here is a list of the vocabulary words students will learn in this lesson plan:

  • Light: a form of energy that is visible when it reflects off the surface of an object
  • Transparent: a term to describe an object that allows light to pass through it, such as air, water, or glass
  • Opaque: a term to describe an object that does not allow light to pass through and instead reflects the light waves off the surface
  • Translucent: a term to describe an object that scatters light waves into different directions
  • Reflection: when light waves encounter a barrier that causes them to return to the original medium
  • Refraction: when light waves change direction upon moving from one medium to another with a different density
  • Diffraction: when light waves stay in the same medium but bend around an obstacle


There are four pages of content in this lesson. At the start, students will learn all about light. They will discover that light is really fast, that it travels at 186,000 miles per second! They will also learn that light can travel through liquids and gases, but it can’t pass through solids. This introduces students to how the properties of different objects cause light to react in a certain way.

The lesson defines reflection as light bouncing off a surface. The amount of light that reflects off the object depends on the object’s traits. A mirror, for example, is so smooth that it easily reflects light. The lesson continues on to define refraction as a wave changing direction when moving from one medium to another. This is what happens when you put an object in water. The object looks distorted because of the various angles of the light waves.

Finally, students will learn about diffraction. Diffraction occurs when a light wave stays in the same medium but bends around an obstacle. The lesson hows a couple diagrams of what this would look like.


The Reflection, Refraction, Diffraction lesson plan includes three worksheets. Each one will help reinforce the concepts that the lesson covers in different ways. The guidelines on the classroom procedure page delineate when to hand out each worksheet to the class.


The activity requires students to work with a partner. Students will create a poster board that displays the three properties of light. They should include diagrams, text, images, and other helpful resources to illustrate each property. In addition, they need to label each property correctly and use the correct terminology. They should also add information if necessary as well as create a catchy title for the poster. The bottom of the worksheet has a blank box that students can use to sketch a rough draft before they begin on the poster itself. After the students finish their posters, they will then present them to the class. You can use the rubric on the worksheet to grade students’ work.


There are two parts to the practice worksheet. The first section displays nine different images. Students must write whether each image represents an example of reflection, refraction, or diffraction. For the second part of the worksheet, there is a list of 10 prompts from the lesson. Students must write which property the prompts relate to. For instance, “a prism” relates to refraction. And “bends around an obstacle” relates to diffraction.


The homework assignment splits into two parts as well. The first 10 questions require students to match terms in a word bank to the statement that they represent. For the second part, students must read 10 statements and decide whether each statement is true (T) or false (F).

Worksheet Answer Keys

The last two pages of the lesson plan document are answer keys for the practice and homework worksheets. The answers are in red for both worksheets. In addition, both of these assignments are fairly straightforward. There should be no variation in students’ responses when comparing them with the answer keys. However, the picture for number 9 on the practice worksheet can be considered both reflection and refraction. Either of these responses are correct. If you choose to administer the lesson pages to your students via PDF, you will need to save a new file that omits these pages. Otherwise, you can simply print out the applicable pages and keep these as reference for yourself when grading assignments.

Additional information


4th Grade, 5th Grade, 6th Grade



State Educational Standards


Lessons are aligned to meet the education objectives and goals of most states. For more information on your state objectives, contact your local Board of Education or Department of Education in your state.

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Great Lesson about Light

This is a wonderful lesson on the concepts of light reflection, refraction, and diffraction. The examples and practice sections help solidify the differences between the vocabulary.