Waves can change directions in three different ways: reflection, refraction, and diffraction.
What is reflection?
Reflection is the change in direction of a wave between two different objects such that the wave returns to the medium from which it began. In other words, the waves are sent back towards the source. Sound waves, light waves, and water waves can all be reflected.
From the image, you can see that reflection is described by a few key terms:
- Incident Ray – the wave/ray traveling towards a surface
- Angle of Incidence – the angle at which the traveling wave/ray hits a surface
- Equal (or Normal) – divides the two rays (incident / reflected) into two equal angles
- Angle of Reflection – the angle at which the reflected wave returns towards the original medium
- Reflected Ray – the wave/traveling away from the “hit” surface, and now traveling towards the original medium
Youtube Video showing incident rays and reflected rays:
What is refraction?
Refraction is the change in direction of a wave (ray) passing from medium to another. Unlike reflection, refracted waves continue traveling through the medium they hit.
One important rule of reaction that can be observed in this example is that the angle of incidence (Theta 1) is always greater than the angle of refraction (Theta 2).
A common experiment to help kids and adults alike to understand refraction is to submerge an object in a bowl of water. Observers will note that the object (e.g., a pen or pencil) will look bent. The light enabling your sight is refracted by the water, which causes your eyes to see a distorted image (of the pen, pencil, or whatever object is submerged).
Diffraction occurs when a wave encounters an object and subsequently bends around the object. A common example is waves that hit a boat or other object. Another practical example of diffraction is noise-cancelling headphones, which use a principle called destructive interference (interference is a result of diffraction) to reduce background noise.
For a fuller explanation, I recommend Professor Dave’s video on Interference, Reflection, and Diffraction:
Books abut Waves
I think these books can be helpful for kids of different ages to learn about waves reflecting, refracting, and diffracting:
The target audience for this book is 6-9 years old. It covers physics topics in addition to reflection, refaction, and diffraction: solar energy, photon particles, and light scattering. Learn more about the book at Amazon.
Light: The Visible Spectrum and Beyond
Another book that goes beyond just RRD. This one aims for audiences beyond just children. It accomplishes that via a series of phenomenal images. The descriptions of the depicted items may not be sufficient to greatly increase an adult’s knowledge, but they are perfect for introducing kids to physics (specifically light). Read more at Amazon.
Let’s Ride a Wave
Let’s Ride a Wave is one of several books in a series authored by Chris Ferrie. Ferrie does a great job introducing physics concepts to young children (ages 4+ can begin to understand the material presented here). The only downside is that the illustrations do not add as much to the book as they should have been able to. However, it’s still an excellent book to pick up to add to your “young learner’s STEM library”.
Hands-On Science: Sound and Light
This Hands-On Science book is an easy-to-understand guide to do 20+ experiments at home.
Seeing the Light: Optics in Nature, Photography, Color, Vision, and Holography
Most of the books on this list have been more targeted towards kids, but if you’re an adult learner, then this is the book for you. The book avoids complicated mathematics, and instead, uses basic analogies to guides readers’ learning about optics and light. This is my favorite book on the topic, and it is available through Amazon or often local bookstores.
Activities Related to Waves Changing Directions
- Quizlet to learn wave vocabulary (including RRD)
- I love this idea to have students write down and draw (see other examples of incorporating writing into STEM) what they see when observing a singer shatter a glass (and talk to your students about how wave reflection ties into it)
Lesson Plans Related to Reflection, Refaction, and Diffraction
Other Key Terms
wave: a disturbance that carries energy from one place to another
wavelength: distance between one point on a wave and the same exact same place on the next wave
frequency: how many waves go past a point in one second (measured in hertz)
amplitude: how far the medium moves from the rest position