11. Waves Flashcards
Define a progressive wave
- An oscillation (vibration) that transfers energy but does not transfer matter
Deinfe mechanical waves
- Progressive waves that need a medium to travel through
Define electromagnetic waves
- Progressive waves that can travel through a vacuum
Examples of mechanical waves
- Sound waves
- Tidal / water waves
- Seismic waves
Examples of electromagnetic waves
- Radio waves
- Microwaves
- Infrared
- Ultralight
- Visible
- Xrays
- Gamma rays
What are mechanical waves composed of?
Mechanical waves are composed of the movement of matter that transfer energy
- As the progressive wave travels through the medium (material) the particles move from their equilibrium position
Define transverse waves
- When energy is transported perpendicular to the direction of oscillation
Define longitudinal waves
- When energy is transported parallel to the direction of oscillation
Describe the characteristics of a wave diagram
- Compression IIIIIIII
- Oscillation <——–>
- Rarefaction I I I
- Energy ——->
Name examples of longitudinal waves
- Sound waves
- P-waves in earthquakes
- Pressure waves
Name examples of transverse waves
- EM waves
- Water waves
Describe the similarities and differences between transverse and longitudinal waves
- Both transfer energy
- Transverse requires a medium, logotidom
Define wavelength (lamda)
- The minimum distance between two points in a phase on adjacent waves
- Units are metres
Define wave displacement (s)
- Distance from the equilibrium position in a particular direction; a vector, so it can have either a positive or negative value
Define amplitude (A)
- Maximum displacement from its equilibrium position
Define frequency (f)
- Number of waves passing a point per unit time
- Units are Hertz or per second
Define time period (period of oscillation) (T)
- The time taken for a wave to move past a given point or the time taken for one oscillation
- Units are seconds
Describe the relationship between frequency and time period
- They are inversely proportional
- f= 1/T
State the equation for wave speed
- v = wave length x frequency
Waves are oscillations therefore we describe the difference between waves with the use of angles in radians
π = 180 degrees
Define in phase
- When a part of the wave continually has the same displacement
- The wave will have a phase difference of 0 or multiples of 2π radians
Define anti phase
- When a part of the wave continually has the opposite displacement
- The wave will have a phase difference of π radians
State the phase difference equation
- The phase difference
pitchfork = x/lamda x 360
Define a ray
- A representation of a wave
- A straight line with an arrow indication the direction of energy transport
Define reflection
- Occurs when a wave changes direction at a boundary between two materials
Define refraction
- Occurs when a wave changes direction and speed when passing from one material to another
- Reflection and refraction both occur when a wave changes direction at boundaries of different mediums
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law and rules of reflection
- ø incidence = ø reflection
- When waves reflect their wavelength and frequency do not change
- A reflected wave gains an additional 90˚ phase difference from the incident wave
- Refraction is when the wave changes velocity (speed and direction)
- If the refracted ray bends towards the normal the wave has slowed down
- When the refracted ray bend away its speed has increased
1) Start with absolute uncertainty
2) Calculate uncertainties in quantities plotted
3) Uncertainty bars for x and y (vertical box plot)
Diffraction and direction
- When a wave passes through a gap they spread out, this is diffraction
- All waves can undergo diffraction
- The speed, wavelength and frequency of a wave does not change when diffraction occurs
- Diffraction only affects the waves direction
The magnitude of diffraction
- The amount of diffraction depends upon two quantities
- Wavelength of a wave
- Size of gap (or obstacle)
- Diffraction is increased when the size of the gap is comparable to the wavelength of the wave
- The relative size of a doorway and the wavelengths of light and sound is why you can hear someone around a doorway but you cannot see them
- Diffraction - only direction changes
- Refraction - refraction, velocity and frequency changes
- Wavelength of sound is compared to width of the door
Polarisation
- Waves are oscillations that transfer energy
- To date we have only considered waves that oscillate in one dimension
- Yet we live in a three dimensional world so it makes sense that the oscillations can be in three dimensions too
Define plane polarised waves
- Waves that oscillate in one plane (one dimension)
Define unpolarised waves
- Waves that oscillate in many possible planes
Is light from a filament lamp polarised or unpolarised?
- Unpolarised
Can longitudinal waves be plane polarised?
- The direction of energy transport is parallel to oscillation
- As their oscillations are limited to on plane it does not make sense to talk about them being plane polarised
- Therefore, we say longitudinal waves cannot be plane polarised
Reflected partial polarisation
- When transverse waves reflected off a surface they become partially polarised
- This means there are more waves oscillating on one particular plane but no completely plane polarised
- Unpolarised light - possible planes of oscillations
- Partial polarised light - Majority of oscillations in this plane
I = P/A
