Chapter 11 Waves 1 Flashcards
Progressive Wave
Transfer energy from one place to another without transferring matter
Transverse Wave
Oscillations perpendicular to direction of energy transfer
Longitudinal Waves
Oscillations parallel to the direction of energy transfer
Why is sound faster through a medium with higher density?
- Air particles are displaced by wave from EP according to force provided by neighbouring particles
In higher density medium:
- As medium’s particles are closer together
- Stronger restoring force
- Energy and vibrations passed more rapidly from one particle to another
Displacement:
Distance from EP in a particular direction
Amplitude
Max displacement of oscillating particle from EP
Wavelength
Minimum distance between 2 points in phase on adjacent waves
Period of oscillation
Time taken for one oscillation
Frequency
Number of waves that pass a given point per unit time
Wave Equation:
V = λf
Frequency Equation
f = 1 / T
Phase difference equation:
ϕ = (x / λ) * 2Π
How can oscilloscope be used to determine wave frequency?
- Using microscope, produce a trace on screen of oscilloscope
- Each horizontal square reps a time interval AKA the timebase
Settings of oscilloscope
- If timebase is 1.0 ms cm^-1, then each square reps a time interval of 1 ms
- A setting of 10 V cm^-1 reps a pd of 10V
Reflection
When a wave changes direction at boundary between 2 different media remaining in original medium
Law of reflection
Angle of incidence = Angle of reflection
What changes happen to a wave when it undergoes reflection?
reFLection
- Frequency and Wavelength DO NOT change
Refraction
When a wave changes direction as it changes speed when it passes from one medium to another
- There is always some partial reflection
What are the rules for waves changing speed?
FAST PEOPLE ARE NOT NORMAL
- If wave slows, then it will refract towards the normal
- If wave quickens, it refracts away from the normal
What are the rules for mediums in relation to the speed of EM and mechanical waves?
EM waves travel slower in more optically dense solutions
Mechanical waves tend to speed up as they enter a physically denser medium
The medium is often the opposite for either
What changes happen to a wave when it undergoes refraction?
reFraction
- Refractions affects wavelengths
- Frequency is constant
Do water waves travel faster in shallower or deeper water?
Think of TSUNAMIs
- Water wave slows down in shallower water
- Wavelength gets shorter
Diffraction:
- Wave phenomena where when waves pass through a gap or travel around an obstacle, they spread out
- All waves can be diffracted
Gap Size in diffraction:
- If wavelength and gap size are similar, it means there is greater diffraction
What changes happen to a wave when it undergoes diffraction?
Nothing changes
Polarisation:
Particles only oscillation along one direction
MEANING
that the wave is confined to a single plane of oscillation
Why can’t longitudinal waves be polarised?
Longitudinal waves have oscillations that are always parallel to direction of energy transfer so wave cannot be plane polarised as oscillations are already limited to only one place
Partial Polarisation
- When transverse waves reflect off a surface, they become partially polarised
- More waves oscillating in one particular place but wave is not completely plane polarised
Intensity
Is defined as the radiant power passing through a surface per unit area
Intensity equation
I = P / A
For a point source:
I = P / 4Πr^2
Relationship between Intensity and Amplitude
Intensity ∝ Amplitude^2
Explain relationship between Intensity and Amplitude:
- Decreased amplitude means reduced average speed of oscillating particles
- Halving amplitude results in particles oscillating with half the speed, and a quarter of kinetic cheeks
- Hence, intensity is directly proportional to the square of an amplitude
EM Waves:
Electric and Magnetic fields oscillating at right angles to each other
Visible Light range:
700nm - 400nm
What is used to polarise microwaves?
A metal grille is used
Refractive Index Equation:
n = c / v
- n is refractive index
Refraction Law:
n sin θ = k
n1 sin θ1 = n2 sin θ2
2 conditions for Total Internal Reflection:
- Light must be travelling from high refractive index to low refractive index
- Incidence Angle > Critical Angle
What happens to light at Critical Angle?
Light refracts along the boundary between 2 media
90 degrees
For air, what is refractive index equation:
sin C = 1 / n
