# wave interference

## standing waves

Waves may reflect off an obstacle that they are unable to pass through. When waves are reflected straight back from an obstacle, the reflected waves interfere with the original waves and create standing waves. These are waves that appear to be standing still. Standing waves occur because of a combination of constructive and destructive interference. Q: How could you use a rope to produce standing waves? A: You could tie one end of the rope to a fixed object, such as doorknob, and move the other end up and down to generate waves in the rope. When the waves reach the fixed object, they are reflected back. The original waves and the reflected waves interfere to produce a standing wave. Try it yourself and see if the waves appear to stand still.

## destructive interference

Destructive interference occurs when the crests of one wave overlap the troughs, or lowest points, of another wave. The Figure 1.2 shows what happens. As the waves pass through each other, the crests and troughs cancel each other out to produce a wave with zero amplitude.

## constructive interference

Constructive interference occurs when the crests, or highest points, of one wave overlap the crests of the other wave. You can see this in the Figure 1.1. As the waves pass through each other, the crests combine to produce a wave with greater amplitude.

## when waves meet

When two or more waves meet, they interact with each other. The interaction of waves with other waves is called wave interference. Wave interference may occur when two waves that are traveling in opposite directions meet. The two waves pass through each other, and this affects their amplitude. Amplitude is the maximum distance the particles of the medium move from their resting positions when a wave passes through. How amplitude is affected by wave interference depends on the type of interference. Interference can be constructive or destructive.

## instructional diagrams

This diagram shows the result of constructive wave interference. The highest point of a waves amplitude is called a crest. The lowest point in amplitude is called a trough. Constructive interference occurs when two waves meet and overlap so that their crests and troughs align. In this image, the crests and troughs of Wave 1 and Wave 2 synchronize. This causes an increase in amplitude. The result is the wave on the right, which has a greater amplitude than Wave 1 and Wave 2.

This diagram shows the results of constructive interference and destructive interference in sound waves. Wave interference is when two waves meet while traveling in opposite directions. The highest point of a waves amplitude is called a crest. The lowest point in amplitude is called a trough. In the example of constructive interference, the crests and troughs of the two waves align. This causes increased wave amplitude when the two waves overlap. In the example of destructive interference, the highest point of amplitude of one wave occurs at the lowest point of the other and cancel each other out. This causes decreased wave amplitude when the two waves overlap.

## questions

wave interference refers to wave interactions that can occur between a wave and

``````a) another wave.

b) its reflected wave.

c) its medium.

-->  d) two of the above
``````

when two waves pass through each other in opposite directions, the interference affects their

``````-->  a) amplitude.

b) frequency.

c) wavelength.

d) two of the above
``````

constructive interference occurs when the crests of one wave overlap the troughs of the other wave.

``````a. true

-->  b. false
``````

destructive interference occurs when the crests of two waves overlap.

``````a. true

-->  b. false
``````

standing waves form only when waves reflect at a 90-degree angle.

``````-->  a. true

b. false
``````

## diagram questions

How many waves occur at the top left diagram?

``````a. 4

-->  b. 5

c. 3

d. 2
``````

How many kinds of waves are shown?

``````a. 1

b. 3

c. 4

-->  d. 2
``````

During interference, what happens to A and B?

``````a. B gets higher and A lower

-->  b. The both are flat and cancel each other out

c. A and B both get higher

d. A gets higher and B lower
``````

How many types of interference is shown in the illustration below?

``````a. 3

-->  b. 1

c. 4

d. 2
``````

How many waves are there before interference?

``````a. 3

b. 4

c. 2

-->  d. 1
``````

What is the resulting amplitude of the wave produced by destructive interference?

``````a. No amplitude

b. No change in amplitude

-->  c. Less amplitude

d. Greater amplitude
``````

What occurs when waves come together in such a way that they completely cancel each other out?

``````a. After Interference

b. During Interference

c. Before Interference

-->  d. Destructive Interferene
``````

What does 1 + 2 produce?

``````a. Really Curvy Line

b. Wavy Line

-->  c. Straight Line

d. Curvy Line
``````

How many Types of wave collisions shown?

``````a. 4

b. 1

c. 3

-->  d. 2
``````

In the illustration below, how many were results of a constructive interference?

``````a. Neither A nor B

b. B only

-->  c. A only

d. Both A and B
``````

What kind of waves cancel each other?

``````a. Non-Harmonic

b. Harmonic

-->  c. Destructive

d. Constructive
``````

What distinguish a constructive interference?

``````a. The waves have the same frequency

-->  b. The waves are in phase

c. The waves have the same amplitude

d. The waves have the same wavelength
``````

Which interference cancels out two waves?

``````a. comparative

b. constructive

-->  c. destructive

d. instructive
``````

How are waves added?

``````-->  a. By amplitude

b. By type

c. By direction

d. By frequency
``````

What do you have when wave amplitudes are canceled?

``````-->  a. zero

b. amplitude

c. wave amplitude

d. zero amplitude
``````

What is the type of interference represented in figure a?

``````-->  a. Constructive

b. Destructive

c. Positive

d. Negative
``````

How do waves become zero?

``````a. when they go in the same direction

-->  b. opposing waves cancel

c. when they have the same period

d. when they have the same wavelength
``````

What kind of interference decreases wave amplitude?

``````a. Constructive Interference

b. In phase wave

c. Out of phase wave

-->  d. Destructive Interference
``````

How many waves are interfering here?

``````a. 3

b. 4

-->  c. 2

d. 0
``````

What happens when two in phase waves combine?

``````a. Destructive interference

b. I don't know

-->  c. Constructive interference

d. Nothing
``````

What degree out of phase causes a destructive interference?

``````-->  a. 180 degree

b. 180 degrees

c. 100 degree

d. 18 degree
``````

What's the result of one wave's crest overlapping the crests of the other wave?

``````a. Destructive Interference

-->  b. Constructive interference

c. Wave Interference

d. Wave Interaction
``````

What happens to the wave during destructive interference?

``````-->  a. waves become flat

b. waves become higher

c. stay the same

d. waves become smaller
``````

Constructive interference occurs because the waves are?

``````a. out of phase

b. different

c. similar

-->  d. in phase
``````

When the crest of one wave meets the trough of another, what happens?

``````a. The result is a lower trough

b. The result is a longitudinal wave

c. The result is higher amplitude

-->  d. The result is a lower total amplitude
``````

Which inference results in resulting wave having increased amplitude?

``````a. sophisticated interference

-->  b. constructive interference

c. destructive interference

d. complimentary interference
``````