Interactions of Waves

Objectives:

1.    Identify examples of reflection, refraction, diffraction, and interference.

2.    Explain some common phenomena using these concepts.

Resources:

Notes:

Interference

# A)                Constructive interference:

·        The crests of the waves line up  (in phase)

·        Results in the sum (+) of the amplitudes of the 2 waves

(library.thinkquest.org/19537/ media/diagram7.gif)

B)                 Destructive Interference: (see pg. 507 for picture)

·        The crests of one wave meet the troughs of another wave (out of phase)

·        Results in the difference(-) of the amplitudes of the 2 waves

Nodes & Antinodes

·        The antinode is the place where maximum energy is displaced during constructive interference.

·        The node is where no energy is displaced due to destructive interference

If a wave has a combination of the 2 it is called a standing wave. A standing wave describes a situation where a wave is reflected so that it appears to be stationary.

(www.udallas.edu/physics/ images/standi41.jpg)

The Doppler Effect:

As you may have noticed at your last trip to the racetrack, the cars engines seem to make a higher pitched sound and as they pass the pitch seems to get lower.  This phenomena can easily be explained by the Doppler effect.  This change in pitch is actually due to a change in frequency.  The change in frequency is due to the added speed of the car.

• The speed of the two vectors are not additive
• The pitch is interpreted as being higher do to the motion of the generator of the sound with respect to the observer.

(www.physicsclassroom.com/ Class/sound/u11l3b1.gif)

As you can see the observer on the right senses an increase in frequency (higher pitch) due to the motion of the police car while the observer on the right senses a decrease in frequency (lower pitch)

The same phenomena can be seen with light. Within the visual spectrum red light has the lowest frequency and violet has the highest frequency.  This phenomena is called blue shift.  Astronomers use it to describe the motion of galaxies and spinning stars.

(www.exploratorium.edu/.../hubble/ tools/images/doppler1.gif)