Question 1

How is a wave defined?

Accepted Answer

a wave is a means for transferring energy via oscillations -while energy moves from one place to another, the waves cause no net movement of any matter

Question 2

How is displacement defined?

Accepted Answer

is the position of a particular point on a wave at a particular instant in time, measured from the mean (equilibrium) position - symbol: various, often x; units:m

Question 3

How is Amplitude defined?

Accepted Answer

is the magnitude of the maximum displacement reached by an oscillation in the wave -symbol (A) units: m

Question 4

How is frequency defined?

Accepted Answer

is the number of complete wave cycles per second -symbol (f) units:hertz, Hz -frequency (Hz) = 1/time period (s) f = 1/T

Question 5

How is wavelength defined?

Accepted Answer

is the distance between a point on a wave and the same point on the next cycle of the wave -symbol (λ) units: m

Question 6

How is period defined?

Accepted Answer

period (also time period) is the time taken for one complete oscillation at one point the wave -symbol T units: s ``` time period (s) = 1/frequency (Hz) T=1/f ```

Question 7

How is phase defined?

Accepted Answer

is the stage given point on a wave is through a complete cycle, measured in angle units, rad -no standard symbol units: rad

Question 8

How is wave speed defined?

Accepted Answer

is the rate of movement of the wave (not the rate of movement within oscillation) - symbol v or c for the speed of electromagnetic waves - units ms^-1

Question 9

What is a mechanical wave?

Accepted Answer

- is one if which there needs to be some sort of material medium - a substance that oscillates to allow the transfer of energy e.g. sound travelling through air

Question 10

What is an electromagnetic wave?

Accepted Answer

- can transfer energy through repeated oscillations of electric and magnetic fields - but these fields so not need matter to support them - the interaction between electromagnetic waves and matter generally slows their transfer e.g. like travels faster in a vacuum that in water

Question 11

How do you calculate wave speed?

Accepted Answer

``` wave speed (ms^-1) = frequency (Hz) x wavelength (m) -v = fλ ```

Question 12

How do you investigate the speed of sound?

Accepted Answer

- using a twin beam oscilloscope,a loudspeakers, two microphones and a ruler - using the twin beam oscilloscope we can find the extra time a sound takes to travel a short extra distance - one beam trace shows a sound picked up by a microphone held 50cm from the loud speaker - the other trace shows the same sound picked up by a second microphone held further from the loudspeaker - the difference in positions of the peaks on the two oscilloscope traces shows the time take, t, for the sound to travel the extra distance d. - then using v=d/t to find the speed - it can be difficult to make accurate measurements from the screen of an oscilloscope so we need to synchronize the traces to minimize the effect of random error in taking measurement - firstly with both microphones at the same distance from the loudspeaker, the two traces appear in identical phase position (in phase) - If we slide the second microphone slowly away from the loudspeaker, we will move the trace out of phase then eventually come back to exact synchronization - at this point, the distance between the two microphones is exactly one wavelength (λ). we set the frequency on the signal generator. and so the wave length equation can be used to find the speed v=fλ

Question 13

how do you measure pulse echo?

Accepted Answer

as the sound has to travel to the object and back it is twice the distance therefore: 2d = v x t so d = (v x t )/2

Question 14

what can pulse echo be used for and why is it useful?

Accepted Answer

- pulse echo ranging and imaging systems are used in a wide range of technological applications from sonar on ships and submarines to air traffic control radar, medical imaging and the measurement of distance to asteroids and to the Moon - this is useful in situations where other methods might be difficult or hazardous e.g. mapping the surface of a planet like Venus

Question 15

How is a transverse wave defined?

Accepted Answer

a transverse wave is one in which the oscillations occur perpendicular to the direction of movement of the wave energy -where the movement of the particles or fields in an electromagnetic wave, are up and down or left and right whilst the energy travels forward

Question 16

How is a longitudinal wave defined?

Accepted Answer

is one in which the oscillations occur parallel to the direction of movement of the wave energy -happens in fluids and are generated by squashing particles together and then stretching them apart from each other repeatedly

Question 17

How is compression defined?

Accepted Answer

is an area in a longitudinal wave in which the particle oscillations put them closer to each other than their equilibrium state -in areas of compression there is higher pressure

Question 18

How is rarefaction defined?

Accepted Answer

is an area in a longitudinal wave where the particle oscillations put them further apart from each other than their equilibrium -in areas of rarefaction there is lower pressure

Question 19

What are Earthquake waves?

Accepted Answer

-also cause seismic waves come in different types primary or P waves and secondary or S waves. These are longitudinal and transverse seismic waves respectively with P-waves travelling faster and arriving first

Question 20

How are wavefronts defined?

Accepted Answer

- are lines connecting points on the wave that are at exactly the same phase position - diagrams for waves are often drawn as lines, where all the points on a line represent points on the wave that are in the exactly same position, perhaps a wave crest - the line showing the direction of travel called a ray must be perpendicular to the wavelength

Question 21

How is constructive interference defined?

Accepted Answer

-is the superposition effect of two waves that are in phase, producing a larger amplitude resultant wave

Question 22

How is destructive interference defined?

Accepted Answer

is the superposition effect of two waves that are out of phase, producing a smaller amplitude resultant wave

Question 23

What is 1 wavelength equivalent to?

Accepted Answer

-1 cycle , 360° or 2π rad

Question 24

What is wave superposition?

Accepted Answer

when waves meet, each wave will be trying to cause a wave displacement at the point of intersection, according to its phase at that location - the net effect is that the overall displacement will be the vector sum of the displacement caused by the individual waves - after the encounter, each wave will continue pass each other, as the energy progresses in the same direction it was originally travelling,

Question 25

What is an example of a wave superposition?

Accepted Answer

multiple small waves coinciding in the same location can lead to a brief very large displacement -the graph is of sea surface height at the Drauper North Sea Oil Platform on 1st January 1995, showing a freak 18m wave

Question 26

How does superposition work in continuous waves?

Accepted Answer

- rather than a single point along the path of a the wave,we consider the waves superposing over an extended space the outcome is a continuous wave that is the sum of the displacement over time in each location - if two waves are in phase (phase difference of 0° or 360° their effect will produce a larger-amplitude resultant wave --> constructive interference - if two waves meet and are exactly out of phase (phase difference of 180 °) then the resultant is a zero amplitude wave --> destructive interference (imaging shining two lights at the same place and at that point you see darkness)

Question 27

How is a stationary wave defined?

Accepted Answer

- stationary or standing waves consist of oscillations in a fixed space, with regions of significant oscillations and regions with zero oscillations, which remain in the same locations at all time - continuous waves travelling in opposite directions will superpose continuously and can set up a stationary wave pattern - the waves need to be of the same speed and frequency with similar amplitude and have constant phase relationships -->coherent - wave energy does not pass through a stationary wave as it is not moving

Question 28

How is coherent defined?

Accepted Answer

waves are to be coherent if they have the same frequency and have a constant phase relationship. Coherent waves are needed to form a stable standing wave

Question 29

How is a progressive wave defined?

Accepted Answer

a progressive wave is a means for transferring energy via oscillation

Question 30

How are nodes defined?

Accepted Answer

nodes are regions on a stationary wave where the amplitude of the oscillations is zero

Question 31

How are anti nodes defined?

Accepted Answer

are regions on a stationary wave where the amplitude of the oscillation is at it maximum

Question 32

What is a sonometer?

Accepted Answer

a sonometer is an apparatus for experimenting with the frequency relationship of a string under tension, usually consisting of a horizontal wooden sounding box and a metal wire stretched along the top of the box

Question 33

How do stationary waves acted when they constructively interact with their own reflection?

Accepted Answer

-the standing wave pattern that can be set up will have a corresponding wavelength, as the wave equation must still be satisfied - imagine a string attached at two ends, these must be it nodes: 1 - the fundamental mode (1st harmonic--> looks like a rainbow) has the wavelength of 2L as the length L from each node is reflected back 2- the 1st overtone (2nd harmonic looks line a sine graph) --> has a wavelength of L as it exactly fits one complete wave in the length of the string (λ=L) 3- the 2nd overtone (3rd harmonic) 1.5 cycles therefore wavelength is 2L/3 4- the 3rd overtone (4th harmonic) 2 cycles therfore has the wavelength of L/2 -- tip to workout out wavelength could the number of peaks and troughs and divide 2L by that number

Question 34

How can you calculate String wave speeds?

Accepted Answer

-waves on a stretched spring travel at a speed that is affected by the tension in the spring, T (in newtons) and the mass per unit length of the string μ ( in kgm^-1), The equation for the speed of a wave in a string is: -v = sqrt(T/μ) if this equation is combined with the wave equation, we get an equation that tells us how the frequency of vibrations is affected by other factors: -v=sqrt(T/μ) and v = fλ -f x λ = sqrt (T/μ) -f=1/λ x sqrt(T/μ) in the fundamental mode of vibration, this means the fundamental frequency f(0) depends on the length of the string, its tension and its mass per until length from: f(0) = 1/2L x sqrt (T/μ)

Question 35

How can you investigate the factors affecting the fundamental frequency of a string?

Accepted Answer

-we can verify the equation -f(0)=1/2L x sqrt(T/μ) experimentally ,in order to confirm it we need to undertake three separate investigations to verify each part of the relationship, whilst maintaining the other variables as control variable: thus we need to verify F(0)∝ 1/L ; F(0) ∝ sqrt(T) and F(0) ∝ sqrt(1/μ) we can use a microphone connected to an oscilloscope to monitor the sound produced by a sonometer string and to measure its frequency of vibration, this can be easier if a data logging computer is used instead of an oscilloscope, s the screen can be frozen for close scrutiny

Question 36

How can you investigate the relationship of f(0)∝1/L?

Accepted Answer

The string support(called bridges) on a sonometer are moveable, so that we can find the frequency with varying lengths, L,whilst keeping the same string (constant μ) and the same hanging mass (constant T) keep the other variables controlled. We can plot a graph to verify F(0) on the y-axis and 1/L on the x-axis which should give us a straight line

Question 37

How can you investigate the relationship F(0)∝ sqrt(T)?

Accepted Answer

-we can find the fundamental frequency using a fixed length of the same string throughout (constant L and constant μ) for varying masses hung over a pulley i.e. varying T. We can plot a graph to verify F(0) on the y-axis is ∝ to sqrt(T) on the x-axis

Question 38

How can you investigate the relationship F(0) ∝ sqrt(1/μ)?

Accepted Answer

- this requires different strings (varying diameter metal wires could be used). Maintaining the same length and mass (constant L and constant T) keeps the other variables controlled. Measure the mass of each wire using digit balance, and its full length in order to calculate the mass per unit length for each wire or string used. - we can plot a graph to verify F(0) on the y-axis is ∝ to sqrt (1/μ) on the x-axis

Question 39

What is diffraction?

Accepted Answer

- diffraction is a spreading of wave energy through a gap or around an obstacle - when a wave passes the edge of an obstacle, if there is a space behind the object which is relatively small, the wave energy can pass around both sides of it and continue travelling past the obstacle - however if the object is larger there may be a shadow region behind it but there will still be diffraction around each edge - if two close obstacles forming a gap then there will be diffraction from each edge of the hap causing the to spread out through the gap

Question 40

What factors affect diffraction?

Accepted Answer

- the amount of diffraction around an obstacle depends on the size comparison between the obstacle and the wavelength of the wave - as a result there is an optimum size of a gap for maximum diffraction --> usually when the gap is the same size as the wavelength - too small --> very little wave energy can pass through - too large --> there is little effect off diffraction as the majority of the wave passes through undisturbed

Question 41

What is the diffraction pattern of light when it goes through a narrow slit?

Accepted Answer

- the diffraction pattern observed when light passes through a narrow slit, shows a central maximum and then areas of darkness and further maxima of decreasing intensity - the gap where there are no lights is an example of an interference pattern from the diffraction --> considering waves bring diffracted from each end of the slit gives us two waves that will meet the screen, at the points the are in phase they will superpose and show light, however when they are out of phase completely there will be no light due to deconstructive superposition - the diffraction pattern is an example of a standing wave on a screen where the dark spots are nodes and the light spots are antinodes

Question 42

In single slit diffraction how does changing the slit size affect the diffraction pattern?

Accepted Answer

a narrower slit widens the central maximum, as well as the further maxima and minima

Question 43

What is a diffraction grating?

Accepted Answer

- a diffraction grating is a device that will case ,multiple diffraction patterns which then overlap creating an interference pattern with a mathematically well-defined spacing between bright and dark spots. - it is a collection of a very large number of slits through which the wave can pass. these splits are parallel and have a fixed distance between each slit - ( CD's have a series of very close lines marked on them and act as the diffraction grating that reflects. This causes the spectrum of colors that can be seen on the from white light that hits the surface

Question 44

What is the diffraction grating equation?

Accepted Answer

the pattern produced by each color passing through a diffraction grating follows the equation: - nλ=dsinϴ - where ϴ is the angle between the original direction of the waves and the direction of a bright spot - λ is the wavelength of the light used - d is the spacing between the slits on the grating ( normally quoted as a number of lines per meter or millimeter so to find d you need to do the initial calculation d = 1/number per metre OR d = (1 x 10^-3)/ number per millimetre - n is called the 'order' the order is the bright spot number from the central maximum which is n=0

Question 45

How can you investigate diffraction with a laser?

Accepted Answer

- a diffraction grating investigation allows careful study of the light making up the spectrum form any light source, Astronomers use this study the spectra from the start - diffraction gratings are manufactured to have a fixed spacing , d, between lines on the grating and this will be printed on the grating - by measuring the angle to each maximum brightness spot created by a diffraction grating,you can calculate the wavelength of the light used from the diffraction grating equation

Question 46

How is interference defined?

Accepted Answer

is the superposition outcome of a combination of waves, an interference pattern will only be observed under certain condition such as the waves being coherent

Question 47

What is two source interference?

Accepted Answer

- a wave meeting its own reflection would set up a standing wave pattern, also known as a interference pattern, - reflection is a convenient way to generate coherent waves that will produce a standing wave - however, any combination of waves that have the same frequency and a constant phase relationship will produce this result - e.g. two loud speakers that are generating the same identical sound waves will have constructive and deconstructive interference

Question 48

What is two-slit interference?

Accepted Answer

- another interference pattern that can be observed if light is shone into an experimental set-up that causes it to create two coherent wave sources that produce a standing wave pattern - this effect was first demonstrated by Thomas Young 1803 using sunlight as the light source - Young explained his experiment using a theory that light can behave as a wave, in classical physics, interference is a phenomenon that can only occur with waves - Young's theory was highly controversial at the time, as he was contradicting Newton's theory that light behaved as a steam of particles - despite the experimental evidence he demonstrated, most scientist at the time refused to believe Young's wave theory of light

Question 49

How can you investigate two source interference?

Accepted Answer

- a ripple tank where plane wave are diffracted through two gaps will cause an interference pattern between the two water waves - another common experimental demonstration of two-slit interference with a laser light

Question 50

How do you explain two-source interference?

Accepted Answer

- each point in a two-source interference pattern will have a superposition result that depends on the phase difference between the waves coming from each source to that point - That phase difference will, in turn, depend on the relative distance to the point from each of the slits compared with the wavelength - the connection between phase difference and the path difference comes if we remember each complete cycle corresponds to 2π radians. - Waves from one slit meeting waves from the other slit at a point will each have had to travel to that point, cycling through wavelengths as they go - thus by comparing the path difference this can be converted into phase difference

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