4.4 Waves 1 Flashcards
What is a progressive wave?
A progressive wave is an oscillation that travels through matter. In some cases they can travel through a vacuum. They transfer energy, not matter.
Why is sound a progressive wave?
Sound vibrations travel to your ears but the air particles do not.
What is a transverse wave?
A wave in which the oscillations or vibrations are perpendicular to the direction of energy transfer.
What is an example of a transverse wave?
Water waves, electromagnetic waves, s-waves produces in earthquakes.
What is a longitudinal wave?
A wave in which the oscillations or vibrations are parallel to the direction of energy transfer.
What is an example of a longitudinal wave?
Sound waves, p-waves produced in earthquakes.
What does compression mean?
A moving region in which the medium is denser/has higher pressure than the surrounding medium.
What does rarefaction mean?
A moving region in which the medium is less dense/has lower pressure than the surrounding medium.
What is the definition of the time period of an oscillation?
The number of wavelengths passing a point per unit time.
Time Period = 1/Frequency (Hz)
How are time period and frequency related?
They are reciprocals of each other.
What is the wave equation?
Wave speed (ms-1) = Frequency (Hz) x Wavelength (m)
What is a wave profile?
A graph showing the displacement of particles in the wave against the distance along the wave.
What is phase difference?
Phase difference describes the difference between the displacement of particles along a wave, or difference between displacements of particles of different waves.
What are the units of phase difference?
Degrees or radians.
What does it mean if two particles are in phase?
If particles are oscillating perfectly in step with each other and both reach maximum positive displacement at the same time, they are in phase.
What does it mean if two particles are in anti phase?
If a particle reaches maximum positive displacement as another reaches maximum negative displacement, they are oscillating completely out of step with each other, and are in anti phase.
How can phase difference be calculated for two points separated by distance x on a wave?
Phase Difference (degrees/radians) = Distance (m)/Wavelength (m)
What piece of equipment can be used to determine the frequency of a wave?
An oscilloscope.
What is the reflection of a wave?
The change in direction of a wave at a boundary between two different media, so the wave remains i the original medium.
What does the ray show on a ray diagram?
The direction of energy transfer and so the path taken by the wave.
State the law of reflection.
The angle of incidence is equal to the angle of reflection.
When a wave is reflected, do wavelength or frequency change?
They stay the same.
What is refraction?
The change in direction of a wave as it passes from one medium to another.
What happens if a wave slows down upon entering a different medium?
It will refract towards the normal.
What happens if a wave speeds up upon entering a different medium?
It refracts away from the normal.
Do sound waves speed up or slow down when entering a denser medium?
Speed up.
Do light waves speed up or slow down when entering a denser medium.
Slow down.
What happens to water waves when they enter shallower water?
The waves slow down and wavelength gets shorter.
What is diffraction?
When waves pass through a gap or travel around an obstacle, they spread out.
Does speed, frequency or wavelength change when a wave is diffracted?
They stay the same.
Under what conditions are diffraction effects most significant?
When the size of the gap/obstacle is approximately the same size as the wavelength.
Why is a very small gap needed to observe diffraction in light compared to sound.
Light has a much smaller wavelength than sound.
What does polarisation mean?
The phenomenon in which oscillations of a transverse wave are limited to only one plane.
What does it mean if a wave is plane polarised?
A transverse wave in which the oscillations are limited to only one plane.
Why can a longitudinal wave not be plane polarised?
The oscillations are always parallel to the direction of energy transfer, so they are already technically polarised.
How is the intensity of a wave described?
Intensity of a wave is defined as the radiant power passing through a surface per unit area.
How is the intensity of a wave calculated?
Intensity (Wm-2) = Radiant Power Passing Through Surface (W)/Cross Sectional Area (m2)
Explain why the intensity of a wave reduces as it spreads out from a point source.
The energy and power spread uniformly in all directions.
What happens to intensity if distance doubles?
Intensity reduces by scale factor 4.
What is the relationship between intensity and amplitude?
Intensity is directly proportional to amplitude².
Are electromagnetic waves transverse or longitudinal?
Complex transverse.
How can electromagnetic waves transfer from the Sun to Earth?
They can travel through a vacuum.
What is an EM wave?
EM waves are electric and magnetic fields oscillating at right angles to each other.
What is the wavelength range for radio waves?
10⁶ - 10⁻¹
What is the wavelength range for microwaves?
10⁻¹ - 10⁻³
What is the wavelength range for infrared?
10⁻³ - 7x10⁻⁷
What is the wavelength range for visible light?
7x10⁻⁷ - 4x10⁻⁷
What is the wavelength range for UV light?
4x10⁻⁷ - 10⁻⁸
What is the wavelength range for X-rays?
10⁻⁸ - 10⁻¹³
What is the wavelength range for gamma rays?
10⁻¹⁰ - 10⁻¹⁶
How are X-rays and gamma rays classified?
By their origin and not wavelength.
What are key properties of EM waves?
- They can be reflected, refracted and diffracted.
- They can be plane polarised.
- All travel at the same speed through a vacuum (3x10⁸ ms-1)
What is the experiment to show that light can be polarised?
- Take 2 pieces of polaroid filter and place them together, rotate and observe the effect of plane polarisation of light passing through the filters.
- When the 2nd filter is turned 90 degrees, intensity falls to 0 as no light is transmitted.
What is an experiment used to show the polarisation of microwaves?
- Any unpolarised microwaves can be polarised like light, but instead of using a polaroid filter, a metal grille is used between a microwave receiver and a microwave transmitter.
How is refractive index calculated?
Refractive Index = Speed of Light Through Vacuum (ms-1)/Speed of Light Through Material (ms-1)
What does it mean if a material has refractive index 1?
Speed of light in the material is equal to speed of light in a vacuum.
From where do you measure the angle of incidence and refraction on a ray diagram?
From the same point on either side of the materials, against the normal.
State the law of refraction.
nsinθ = k
n = refractive index
θ = angle between normal and incident ray.
k = constant
What is total internal reflection?
The reflection of all light hitting a boundary between two media back into the original medium, when the light is travelling through the medium with the higher refractive index, and the incidence angle at the boundary is greater than the critical angle.
What is an experiment used to determine the refractive index of a material?
- Direct a ray of light with a ray box toward the centre of a semi-circular block and where the light enters at 90 degrees and, where the light doesn’t change direction is where the angles are measured correctly.
- Use the refractive index equation.
Describe the basic principle of an optical fibre.
- A simple optical fibre has a fine glass core surrounded by glass cladding with a lower refractive index.
- Light travelling through the fibre is contained within the core because of total internal reflection at the core/cladding boundary.
- Simple optical fibres are step indexed, n changes suddenly between the core and cladding, and between the cladding and air.
