Interference pg. 63

Objectives Physics terms Investigate wave interference. Describe constructive and destructive interference. superposition principle interference constructive interference destructive interference phase

Multiple waves Examine this picture of the ocean. Notice that there are ripples on top of the waves. These ripples are actually smaller waves that are combining with larger waves. Waves of different amplitudes, wavelengths, and frequencies are often present at the same time. The sounds in a classroom are another example of waves of many different amplitudes, wavelengths, and frequencies are all present at the same time.

Rogue waves How are small ripples and the huge walls of water called “rogue waves” related? The answer lies in an understanding of interference.

Wave Interference Interference occurs when two waves meet while traveling along the same medium Interference causes the medium to take on a shape that results from the net effect of the two individual waves upon each other Consider two pulses of the same amplitude traveling in different directions along the same medium, the result of their interaction (interference) is the focus of this lesson.

Superposition principle The superposition principle says that the total amplitude at any point equals the sum of the amplitudes of all of the waves that occur at that same place and time.

Constructive interference Constructive interference occurs when the interfering waves have displacement in the same direction. The result is a larger amplitude wave.

Destructive interference Destructive interference occurs when the interfering waves have displacements in opposite directions. The result is a smaller amplitude wave. If the amplitudes are exactly matched, there can be total destructive interference.

After interference The result of the interference between the waves is not permanent. Once the waves pass through each other they resume their previous anatomy & continue doing what they were doing before the interference.

Temporary interference Two opposite pulses start at opposite ends of this spring. When they meet in the middle, they cancel. They re-appear after passing through each other.

Homework Which of the following is not an example of wave interference and the superposition principle? A car muffler produces sound to counteract noise from the engine. Ocean waves hit the shore and are absorbed by the beach. Noise-canceling headphones eliminate background noise by producing sound that is out of phase with the background noise. Light shown through two thin slits creates a diffraction pattern.

Homework Describe how two wave pulses can combine destructively.

Homework In your own words, describe the difference in appearance between a wave with a single frequency and a wave composed of more than one frequency.