WAVES (PART 2) Flashcards
1
Q
- How is an expression for a Wave given?
A
- ω = angular frequency
- positive sign = the wave moves towards the
left
= this is a negative x direction - negative sign = the wave moves towards the
right
= this is the positive x direction - A = wave amplitude
- k = wave number
2
Q
- How is the wave number (k) calculated?
A
k = 2π / λ
3
Q
- How is the Angular Frequency (ω) calculated?
A
- ω = 2 . π . f
4
Q
- What is the phase of the wave?
A
- the argument of the cosine function
5
Q
- How can we vary the phase in the expression?
A
- we can change the point under the observation
- this means that we change the x value
- we can change the time at which a particular point is
observed - we do this by changing the t value
6
Q
- What happens when two waves of the same type meet and overlap?
A
- type = frequency
- the waves will superpose
- a new oscillation will be created
7
Q
- Which kinds of sound waves give rise to easily observed interference effects.
Interference effects are shared points where both the waves pass through.
A
- two sound waves
- each of the same frequency and the same wavelength
8
Q
- When are two waves said to be in phase?
A
- when the crest of one wave falls on the crest of the
other - these waves are identical
9
Q
- What happens when waves are in phase?
A
- the waves reinforce each other
- they give rise to a high intensity at the point where the
one crest of the wave falls onto the other - this is known as a COMPLETE CONSTRUCTIVE
INTERFERENCE
10
Q
- What will cause two waves to cancel each other out?
A
- the crest of one wave falling on the trough of the
other wave - these waves are identical
- this is known as COMPLETE DESTRUCTIVE
INTERFERENCE
11
Q
- What happens during Complete Destructive Interference?
A
- there will be no sound heard at the point where
the two waves cross one another - these waves are 180° out of phase
12
Q
- What are Intermediate effects in terms of Destructive Interference?
A
- this is when two waves are neither in phase
- nor are they 180° out of phase
- these waves have a fixed relationship in between
13
Q
- Destructive interferences and constructive interferences consist of identical waves.
What does this entail?
A
- they have the same amplitude
- they have the same frequency
- they have the same amplitude
14
Q
- What produces alterations of maximum and minimum intensity?
A
- they are produced by the superposition of two waves
- these two waves have slightly different frequencies
- these frequencies are known as beats
15
Q
- What are beats?
A
- they are the oscillations in the amplitude
- they are found in a superimposition wave
- they express the loudness of the sound
16
Q
- What can be said about waves that are formed by superimposition?
A
- they are formed by the superimposition of two waves
- these two waves have slightly different frequencies
17
Q
- What are 2 important frequencies with regards to waves created by the superimposition of two non-identical waves?
A
FREQUENCY ONE:
- this is the actual frequency of the resulting disturbance
- this is known as the Carrier Frequency
FREQUENCY TWO:
- this is the frequency with which the maximum
amplitude of the superimposition wave changes
18
Q
- What is the Beat Frequency?
A
- this is a frequency
- it is a frequency at which the maximum amplitude of
the superimposition wave oscillates/changes
NB: the number of beats per second is equal to the
difference in frequency
19
Q
- How is the Beat Frequency calculated?
A
- fb = |f1 - f2|
- f1 and f2 are the frequencies in hertz of the two
component waves
20
Q
- In sound waves, what is the result of a pressure disturbance?
A
- the ear hears a pressure disturbance as the average
frequency - this will change the loudness at the beat frequency
21
Q
- What leads to a slower beat frequency?
A
- a smaller difference between the frequencies of the two superimposing waves
22
Q
- When is reflection observed?
A
- when the water waves hit a wall of some sort
- when light waves hit a mirrored surface
23
Q
- What are the two types of reflection determined by?
A
- the kind of barrier that the wave encounters
TYPE 1:
- waves that have an attachment point that is fixed
TYPE 2:
- waves that have an attachment point that is not fixed
24
Q
- What happens to waves that have a fixed attachment point?
A
WHEN THE STRING IS NOT ABLE TO MOVE AT THE POINT OF ATTACHMENT:
- the reflected wave is inverted
- it travels back along side the strong
- it travels upside down
- the wave is equal in magnitude
- it is always in opposite direction at the attachment
point
25
Q
- What happens to waves that have an attachment point that is not fixed?
A
WHEN THE ATTACHMENT POINT IS NOT FIXED:
- the reflected pulse travels back
- it travels back along the wave
- it has the same orientation as the incoming wave
- the incoming and reflected waves will superimpose
- they do this at the attachment point
THESE WAVES:
- have twice the magnitude of the incoming wave on its
own
26
Q
- What is a Standing Wave
A
- it composes of two waves
- these waves have the same wavelength
- they have the same speed
- the have the same frequency
- they are travelling in opposite directions
- they travel through the same medium
27
Q
- How are Counter Propagating waves formed?
A
- through reflection
- the reflected and incoming waves are propagating in
opposite directions
28
Q
- What are Standing Waves formed by?
A
- they are formed by multiple reflections between two barriers
29
Q
- What does the Green Waveform represent?
A
- it represents the Standing Wave
- this results from the counter propagating waves
30
Q
- What happens to the peaks of the Standing Waves (Green Waves)?
A
- they do not propagate left or right
- they only oscillate up and down
- this is why they are known as Standing Waves
31
Q
A
