Module 4: Chapter 11 - Waves 1 Flashcards
What is a progressive wave?
A progressive wave is a means of transferring energy and infromation form one place to another without a transfer of matter between the 2 points
What are the 2 types of progressive waves?
- Transverse
- Longitudinal
What is a transverse wave?
A transverse wave is a wave in which the direction of oscillation of a wave is perepndicular to the direction of motion of the wave
Describe the structure of a transverse wave
- The direction of oscillation of the wave is perepndicular to the direction of motion of the wave
- They have peaks and troughs where the oscillating particles are at a maximum displacement from their equilibrium position
What are longitudinal waves?
Waves in which the direction of oscillation of the wave is parallel to the direction of motion of the wave
Describe the structure of a longitudinal wave
- The direction of oscillation of the wave is parallel to the direction of motion of the wave
- They have areas of compression and rarefaction where the oscillating particles are at a maximum displacement from the equilibrium position
Why is the speed of sound faster through a medium with higher density?
The particles are closer together and therefore there are stronger restoring forces and the vibrations are passed more rapidly from one particle to the next
What is displacement (in a wave)?
The distance from the equilibrium position in a particular direction, it is a vector and can therefore be both positive and negative
What is amplitude?
The maximum displacement from the equilibrium position
What is wavelength?
The minimum distance between 2 points in phase on adjacent waves, for example, the distanec from one peak to the next or from one compression to the next
What is the period of oscillation?
The time taken for one oscillation or for the wave to move one wavelength past a given point
What is frequency?
The number of wavelengths passing a given point per unit time
What is wave speed?
The distance travelled by a wave per unit time
What is a wave profile?
A graph showing the displacement of particles within the wave against the distance along the wave
What can a wave profile be used to determine?
- Wavelength
- Amplitude
What is a displacement-time graph? (waves)
A graph of the displacement of particles within the wave agsinst the time
What can a displacement-time graph be used to determine about waves?
- Time period / Frequency
- Amplitude
What is the wave equation?
v = fλ
What is phase difference?
Phase difference describes the difference between the displacements of the particles along a wave, or the difference between the displacements of the particles on different waves. It is measured in degrees or radians
What is the equation for phase difference in degrees?
φ = 360(x/λ)
x = distance between 2 points on a wave
What is the equation for phase difference in radians?
φ = 2π(x/λ)
x = distance between 2 points on a wave
What is the phase difference between X and Y?
π/2 radians OR 90°
What is the phase difference between X and Y?
π/2 radians OR 90°
What is the phase difference between X and Y?
π radians OR 180°
How can you determine the speed of sound in air?
- Set up the apparatus as shown
- Play a constant known frequency from the speaker
- Move the receiver until the waves are perfectly in phase or antiphase and record the distance between the speaker and microphone
- To determine the wavelength of the wave divide the distance by the number of wavelengths along (if it is in phase it will be an integer, if it is antiphase it will be .5 value)
- Repeat this and find a mean average for the wavelength
- Calculate wave speed using v = fλ
What is reflection?
Reflection occurs when a wave changes direction at a boundary between 2 different media, and remains in the original medium. The wavelength, frequency, and speed of the wave are completely unchanged
What is the law of reflection?
The angle of incidence is equal to the angle of reflection when measured to the normal
What is a wavefront?
A line joining points on a wave which are in phase
What is refraction?
Refraction occurs when a wave changes direction as it changes speed when it passes from one medium to another. The amount of refraction depends on the refractive index of the material
What happens to the properties of a wave in refraction?
- Frequency = NO change
- Wavelength + Speed = Change
What happens when a wave enters shallower water?
When a wave enters shallow water, it will slow down, the wavelength will decrease and it will bend towards the normal
What is the equation for refractive index?
n = c/v
refractive index = speed of light in vacuum / speed of light in material
What happens if the refractive index of a material is increased?
The speed of light in the material will decrease, causing the wavelength to decrease and the light to bend towards the normal
What happens if the refractrive index of a material is decreased
The speed of light in the material will increase, causing the wavelength to increase and the light to bend away from the normal
What is snells law?
n₁ sinθ₁ = n₂ sinθ₂
A swimming pool changes in depth from the shallow end to the deep end. Draw a wavefront diagram to show how circular ripples from a source travel from the deep to the shallow end.
A swimming pool changes in depth from the shallow end to the deep end. Draw a wavefront diagram to show how circular ripples from a source travel from the shallow to the deep end.
What are the limitations of optical microscopes?
You cannot continue to magnify an object as at high magnifications the image gets blurry. This is due to diffraction of the light as it passes through the aperature of the microscope
What is diffraction?
Diffraction is the spreading out of a wave as it passes through an aperture or when they encounter an obstacle
How do the properties of a wave change with diffraction?
- Direction does change
- Speed, wavelength, and frequency do NOT change
How does the size of the aperture effect diffraction?
Diffraction will only occur if the wavelength of the wave is of a similar size to the size of the aperture
How does wavelength affect diffraciton?
Greater wavelength = greater diffraction
What is polarisation?
The polarisation of light means that the particles oscillate along one direction only, which means that the wave is confined to to a single plane
What is unpolarised light?
Light which oscillates in ma y different planes
What is polarised light?
Light which oscillates in one plane only
What type of waves can be poalrised?
Transverse waves ONLY
Why can EM waves be polarised but sounds waves cannot be polarised?
EM waves are transverse waves meaning they can be polarised as they oscillate in many different planes, however sound waves are longitundinal waves meaning they cannot be polarised as they are already confined to a single plane
What is partial polarisation?
Partial polarisation is when there are more oscillations in one particular plane, but the wave is not completely plane polarised
How does partial polarisation occur?
Partial polarisation occurs when light is reflected off non-metallic surfaces. The extent to which polarisation occurs if dependent upon the angle of incidence and the material of the surface.
Why may you see a glare on asphalt, snow, and water?
Non-metallic surfaces such as asphalt, snow, and water reflect light such that there is a large concentration of vibrations in a plane parallel to the surface. Therefore, you may perceive a glare. However, wearing polarising sunglasses can signifigantly reduce this glare ass they only allow light oscillating in one plane to pass through them.
What are 2 examples of transverse waves?
- EM waves
- S-waves
Explain why the diffraction of sound is regularly observed but less frequently observed for lught
Sound waves may more often pass through an aperature of similar size to their wavelength. However, the wavelength of light is much smaller than most gaps and is therefore not observed as often
Explain why it is possible to receive long-wavelength radio signals at the bottom of some valleys in which the higher-frequency TV signals cannot be received
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A higher frequency wave means it has a smaller wavelength. Radio waves have a longer wavelength and they therefore diffract over the hill reaching the bottom of the valley as the valley is of a similar length to the wavelength. However, as the TV signal has a shorter wavelength, it does not diffract as signifigantly and therefore does not reach the bottom of the valley
What is the intensity of a wave?
The radiant power passing through a surface per unit area
What are the units for intensity?
Wm⁻²
What is the equation for intensity?
I = P/a
Intensity = power / area
What is the relation between the intensity of radiation received and the distance from the source (r)?
I = P / (4πr²)
How is the equation “I = P / (4πr²)” derived?
I = P / a
Surface area of sphere = 4πr²
I = P / (4πr²)
What is the total power output of the sun if the intensity of radiation received by the upper atmosphere is 1400 Wm⁻²? The average distance between the Earth and the SUn is 150 million km
3.96x10²⁶ W
What is the relationship between intensity and amplitude?
Intensity is directly proportional the amplitude squared
I ∝ A²
Describe Electromagnetic waves?
- All EM waves travel at the speed of light, therefore the wave equation for EM waves is c = fλ
- EM waves can travel through a vacuum, no medium is required to travel through
- EM waves with high frequency have high energy
- All EM waves are transverse waves
What is the electromagnetic spectrum in order of increasing wavelength?
- Gamma rays
- X-rays
- Ultraviolet
- Visible
- Infrared
- Microwaves
- Radio waves
What is the electromagnetic spectrum in order of increasing frequency?
- Radio Waves
- Microwaves
- Infrared
- Visible
- Ultraviolet
- X-rays
- Gamma rays
What is the range of wavelengths for Radio waves?
1x10⁻¹ - 1x10⁶ m
(>1x10⁻¹)
What is the range of wavelengths for Microwaves?
1x10⁻³ - 1x10⁻¹ m
What is the range of wavelengths for Infrared?
7x10⁻⁷ - 1x10⁻³ m
What is the range of wavelengths for Visible light?
4x10⁻⁷ - 7x10⁻⁷ m
What is the range of wavelengths for Ultraviolet?
1x10⁻⁸ - 4x10⁻⁷ m
What is the range of wavelengths for X-rays?
1x10⁻¹³ - 1x10⁻⁸ m
What is the range of wavelengths for Gamma rays?
1x10⁻¹⁶ - 1x10⁻¹⁰ m
(<1x10⁻¹⁰)
What are the 4 properties of EM waves?
- Reflection
- Refraction
- Diffraction
- Polarisation
What property of EM waves confirms that they are transverse waves?
They can be plane polarised
Which 2 regions of the EM spectrum overlap and why?
X-rays and Gamma rays overlap, this is because they are not defined by their wavelengths (as the other regions are), but instead by how they are formed. Therefore there is a slight overlap
How are X-rays formed?
When an electron is slowed down from a high velocity
How are gamma rays formed?
Through radioactive decay
What is Malus’ law?
The intensity of a beam of plane polarised light after passing through a rotatable polariser varies as the square of the cosine of the angle through which the polariser is rotated from the position which gives the maximum intensity
What is the equation from Malus’ law?
I = I₀cos²θ
I = intensity after passing through the filter
I₀ = original intesity
θ = angle from the position which gives maximum intensity
Sketch a graph of I against θ of a polarised light as a metal grille is rotated
When are microwaves already plane poalrised?
When they are artificially produced
What is the equation for relative refractive index?
Relative refractive index = n₂/n₁
What are the conditions for total internal reflection?
- The original material must have a higher refractive index that the surrounding material (i.e glass to air)
- The angle of incidence must be greater than the critical angle
What is the critical angle?
The angle of incidence at the boundary between 2 media that will produce an angle of refraction of 90°
Sketch a diagram showing light approaching the boundary between glass and air when the angle of incidence is less than the critical angle
Refraction and partial reflection occurs
Sketch a diagram showing light approaching the boundary between glass and air when the angle of incidence is equal to the critical angle
Light refracts along the boundary between 2 media and partial reflection occurs
Sketch a diagram showing light approaching the boundary between glass and air when the angle of incidence is greater than the critical angle
Total internal reflection
What is the relationship between the refractive index of the medium and the critical angle as light travels from the medium into air?
SinC = 1/n
C = critical angle, n = refractive index
What is the critical angle for ice whose refractive index is n = 1.309?
49.8°
What changes in reflection?
- Direction
- Amplitude
What are the 2 types of waves produced in an earthquake?
- P-waves
- S-waves
What is an S-wave?
An S-wave is a “secondary wave” produced in an earthquake. They are transverse waves.
What is a P-wave?
A P-wave is a “Primary wave” produced in an earthquake. They are longitudinal waves.
What is the equilibrium position?
The resting posiiton of waves or particles in an oscillation
What is a restoring force?
A force that tries to return a system to its equilibrium position. In a wave a displaced particle experiences a restroing force from its neighbours and it is pulled back to its original positon
What is an area of compression in a longitudinal wave?
A moving region in which the medium is denser or has higher pressure than the surrounding medium
What is an area of rarefaction in a longitudinal wave?
A moving region in which the medium is less dense or has less pressure than the surrounding medium
What is antiphase?
When there is a phase difference of 180° or π radians. They are oscillating completely out of step with each other. One of the particles reaches its maximum positive displacement as the other reaches its maximum negative displacement
What is in phase?
When there is a phase difference of 360° or 2π radians. The particles are oscillating perfectly in step with each other. They both reach their maximum positive displacement at the same time. This occurs when they are separated by one whole wavelength
What is a ray?
A line representing the direction of energy transfer of a wave, perpendicular to the wavefronts
Why cant longitundal waves be polarised?
The oscillations are always parallel to the direction of energy transfer, therefore, the oscillations are already confined to a single plane and they cannot be polarised
Describe the structure of an EM wave
Oscillating magnetic and electric fields perpendicular to both each other and the direction of propogation
How can an EM wave be polarised?
By using a polarising filter. These filters only allow waves of particular orientations to pass through
How can microwaves be polarised?
Using a metal grille
How is the polarisation of EM waves used in communication transmitters?
In order to reduce the interference between different EM transmitters, some may transmit vertically plane polarised waves, whereas others may transmit horizontally plane polarised waves. An aerial can then be aligned to detect either the horizontal or vertical waves and will suffer less interference from the other waves
What is the equation for critical angle?
IMPORTANT
Sin C = n2/n1
What is it called when white light is split up to form a spectrum?
Dispersion
