Notes 3: The Behavior of Waves Chapter 10 Section 3 (page 303)

What You’ll Learn State the law of reflection. Explain why waves change direction when they travel from one material to another. Compare and contrast refraction and diffraction.

Why It’s Important You can hear an echo, see shadows, and check your reflection in a mirror because of how waves behave.

Review Perpendicular - a line that forms a 90-degree angle with another line.

Reflection All waves - including sound, water, and light waves - can be reflected. Reflection happens in two steps: A wave strikes a surface. The wave bounces off the surface and moves back from where it came. (ex. echo)

The Law of Reflection The beam striking a surface is called an incident beam. The beam bouncing off the surface is called the reflected beam. The Law of Reflection states that angle of incidence is equal to the angle of reflection.

Refraction Refraction - the bending of a wave as it changes speed in moving from one medium to another. Remember that a wave’s speed depends on the medium it is moving through. When a wave passes from one medium to another (like air to water in this photo) it changes speed. The greater the change in speed is, the more the wave bends.

Refraction

Diffraction When waves strike an object, several things can happen: The waves can bounce off a surface or be reflected. If the waves can pass through an object, the can refract. Waves can BEND AROUND the object. Diffraction - the bending of waves around an obstacle; can also occur when waves pass through a narrow opening.

Diffraction and Wavelength The amount of diffraction that occurs depends on how big the obstacle or opening is compared to the wavelength of the wave. When an obstacle is smaller than the wavelength, the waves bend around it. (like sound bending around a corner) When the obstacle is larger than the wavelength, the waves don’t bend around it. (like light not bending around a corner)

Diffraction

STanding Waves Standing Wave - a wave pattern that forms when waves of equal wavelength and amplitude, but traveling in opposite direction continuously interfere with each other; has points called nodes that do not move.

Summary When reflection of a wave occurs, the angle of incidence equals the angle of reflection. Refraction occurs when a wave changes direction as it moves from one medium to another. Diffraction occurs when a wave changes direction by bending around an obstacle. The effects of diffraction are greatest when the wavelength is nearly the obstacle size.