Reflection and Refraction of Waves
Conceptual Physics
When waves interact with matter, the energy of the waves can be reflected, absorbed, transmitted or
a combination of all three. Provide examples of each:
Reflection - a wave phenomenon in which the energy of a wave is deflected (redirected) after striking
a boundary between two media (an interface).
Reflection was observed in the ripple tank. How did the waves behave when they were reflected?
Incident wave –
How does reflection of waves impact our lives?
Most of what you see is reflected light – What is needed to see?
A Ray of Light.......... How does a ray of light move?
Reflected wave -
In class activity:
Part 1: Which direction do reflected objects go?
Roll a marble/rubber ball against a perpendicular target from various positions. Record it’s path
toward the target. Record the path away from the target. Perform 3 trials, from the spots referenced in
the diagrams below.
target on wall
Questions:
1. Where must the ball be in order for it to bounce back to it’s original position?
2. What happens to the reflected path as the ball rolled in at a greater angle?
3. Measure the angle between the center line and the incident roll. Measure the angle between the
center line and the reflected roll. How do the two angles compare?
Part 2: Where do images appear?
Place an object in a square on the graph paper in front of the mirror. Count how many squares are
between the object and the mirror surface. Look in the mirror and count how many squares are from
the mirror surface to the image.
Plot the location of the object and the image in your graph paper, labeling real space, the object,
virtual space and the image.
Hold a ruler next to the object and measure it. Now observe the image. How big does the image
appear?
Do this two more times with the object in different locations.
Questions:
1. What is the relationship between the distance from the object to the image and the object to the
mirror?
2. How does the image size compare the object size?
How does
Refraction - The "bending" of a wave as the
wave moves from one medium into another.
What happened in the ripple tank when we observed refraction?
The waves moved from deep to shallow water.
(a change in medium: deep to shallow causes the velocity to change)
The wavelength decreased.
(Since the velocity changed and the frequency remained constant)
Why does refraction occur?
As the wave moves from one medium to another, the velocity of the wave
changes. Since the
frequency does not change, the wavelength must change as the velocity changes.
If the wave does not hit the boundary layer (interface) straight on, one edge of the wave
front
changes velocity
before the other, causing the direction of the wave to change. If the wave front
encounters the interface straight on, the entire wave front changes velocity at the same time and the
ray continues in a straight line.
Refraction Activity: Draw the pathway of a light ray as it moves from air into a lucite (plastic) block,
back into air again.
Procedure:
Place a lucite block on the template below. Place a pin at the beginning of the ray and at the end of
the ray on the right side of the block. Look through the left side of the block and swivel your paper
until the two pins in the block are aligned. Mark the spot on the front side of the block with a pin, and
then again with a second pin closer to you. Remove the lucite block and draw lines connecting the
dots. Draw arrows showing the direction the ray is moving.
Diagram of a Refracted Ray and definitions…
Interface –
Normal Incident ray Angle of incidence Refracted ray
Angle of refraction -
What happens as the ray moves from a fast medium to a slow medium?
What happens as the ray moves from a slow medium to a faster medium?
Can a ray always “escape” from a slower medium?