Wave interactions pg. 61

Objectives Examine and describe wave propagation. Investigate behaviors of waves: reflection, refraction, and diffraction. Describe the role of wave characteristics and behaviors in medical and industrial applications. Physics terms crest trough wavefront propagation reflection refraction diffraction absorption

Propagation To propagate is to spread out and grow. Waves propagate outwards from their source, carrying both energy and information. How do waves propagate?

Waves propagate because of connections between the particles in the wave medium. A disturbance in one place causes a disturbance in the adjacent matter, such as in this water wave below. How waves propagate

Boundary Behavior Once a wave has propagated out from its source, it will continue moving until it runs into an barrier or the medium its traveling through ends & in some cases another medium begins. Despite what you might initially think, a wave doesn't just stop when it reaches the end of the medium or barrier, instead it will act/behave a certain way. The behavior a way shows when it reaches a boundary or change in medium is the focus of this lesson.

In Investigation 15B you will explore wave propagation and wave interactions in a simulated ripple tank. The simulation displays wave behavior using a wavefront representation. Get logged into ergopedia Click on the ‘Interactives’ tile (the one that has a computer mouse on it) Scroll down to Ch.15 & click on ‘Wave Interactions’ Wait for further instructions Exploring the ideas

Investigation  Reflection Part 1: Investigate reflection 1.Press [Run] to watch the waves propagate. 2.Change wavelength and/or frequency. Press [Run] to see the new simulation. 3.Repeat the simulation for three different boundaries: angled wall curved concave wall curved convex wall

Investigation  Reflection Questions For the flat boundary reflection o How does the wave direction change as it reflects off the boundary? For the angled boundary reflection o How does the wave direction change as it reflects off the boundary? For the curved boundary reflection o How does the wave direction change as it reflects off the concave wall? o How does the wave direction change as it reflects off the convex wall?

Investigation Part 2: Investigate refraction, diffraction, and interference 1.Investigate refraction of plane waves for flat and angled boundaries. 2.Investigate diffraction of plane waves around a half wall, and through single and double gaps. 3.Investigate diffraction by varying the wavelength for the single-gap wall. 4.Investigate absorption using a flat boundary. 5.Investigate interference using two circular waves.

Investigation Part 2 Questions Refraction How does the refracted wave vary for a flat vs. angled boundary? Diffraction o How does the diffracted wave vary between a single gap & double gap boundary? o Vary the wavelength of the wave for a single gap diffraction, how does the diffracted wave change? Absorption What happens when the boundary absorbs the wave?

Reflection Reflection involves a change in direction of a wave when it bounces off a barrier. In some cases the shape of the wave might change as well. In general whatever angle a wave approaches a barrier at, its reflection angle will be the same.

Reflection occurs at boundaries where conditions change — such as the edge of a pool or a wall in a room. Boundaries

Curved boundaries alter both the shape and direction of a wavefront. Curved boundaries They can turn plane waves into circular waves that converge at a point. They can also change the curvature of a circular wave.

Reflection is used in many technologies. Concave reflectors are employed extensively in communications technology such as satellite dish receivers. This convex reflector provides an expanded view for a bus driver. Concave reflectors are also used to focus the headlights of cars. Is reflection useful?

Refraction of waves involves a change in the direction of waves as they pass from one medium to another. Refraction The speed of a wave depends on the properties of the medium it’s traveling through. So if the medium (and its properties) is changed, the speed of the waves is changed. Because the wave path bends, the wave also experiences a change in wavelength (& therefore speed).

Refraction  Water Waves Water waves refract if the depth changes. Water waves travel fastest when the medium is the deepest. So, if water waves are passing from deep water into shallow water, they will slow down. This decrease in speed also leads to a decrease in wavelength.

Waves move fast in deep water. A-B moves slower in shallow water. A-C moves slower in shallow water. Refraction of a water wave Shallow (slow)

Refraction changes the direction of a wave. Refraction and direction

Refraction also changes the wavelength of a wave. Refraction and wavelength Notice: as the wave slows down, its wavelength gets shorter.

Recall: When wave velocity changes during refraction, the wavelength also changes. But frequency CAN’T change: Refraction and frequency Every wave that enters the boundary must exit the boundary. Therefore, the number of waves per second must stay constant.

Refraction is important in many technologies: In optical systems such as cameras, telescopes, and eye glasses, lenses refract light waves. Ultrasound imaging detects changes in tissue density by reflecting AND refracting very high frequency sound waves. Is refraction useful?

Diffraction often changes the direction and shape of a wave. Diffraction Diffraction is a property of waves that allows them to bend around obstacles and pass through gaps. The amount of diffraction (the sharpness of the bending) increases with increasing wavelength and decreases with decreasing wavelength. In fact, when the wavelength of the waves is smaller than the obstacle, no noticeable diffraction occurs.

Diffraction Longer wavelengths = more bending. When the wavelength is large compared to the gap, the waves diffract in complete arcs. When the wavelength is small relative to the gap, there is less diffraction and a larger “shadow zone”.

you are here You are around the corner from a lamp and a speaker. Sound and light are both waves, and both can diffract. You can hear the speaker but not see the lamp. Why? A paradox

Diffraction Longer wavelengths = more bending. Sound waves diffract around corners because sound waves have long wavelengths of centimeters to meters. Light waves also diffract, but their wavelength is much smaller (~10 -5 cm), so the diffraction is imperceptibly small. Light casts sharp shadows.

Radio waves have long wavelengths (10 to 1000 m long). This allows them to diffract around obstacles such as mountains. Cell phones use much shorter wavelengths (6 – 12 cm), so cell phone transmissions diffract (spread) less. You need line-of- sight from the phone to the tower for transmission. Diffraction in technology

1.Define the following events as fitting one of the wave-boundary interactions. Use each term (reflection, refraction, absorption, and diffraction) once. Homework a.Tarmac heats up on a sunny day. b.A magnifying glass enlarges an image. c.Waves curve around a boulder in the water. d.A yell echoes off a building. absorption refraction diffraction reflection

a.wave speed b.Wavelength c.frequency 2.A water wave moves from deep to shallow water. Describe changes that occur to the following characteristics of the wave as it crosses the boundary from deep to shallow water: Homework The wave speed decreases. The wavelength decreases. The wave frequency does NOT change.

a.Describe the wave behavior that allows you to hear sound from another room through a crack in the door. b. Describe the wave characteristic that makes radio transmission possible. Diffraction causes sound waves to spread through a door, so you can hear from another room. 3.Wave behaviors and characteristics: Homework Radio waves have long wavelengths that allow them to bend (diffract) around obstacles.