3 WAVES Flashcards
Unit for temperature
Degrees
Unit for frequency
Hertz (Hz)
Unit for distance
Metre (m)
Unit for speed
Metre/second (m/s)
Unit for time
Second (s)
Difference between longitudinal and transverse wave
Transverse waves oscillate perpendicular (90) to the direction of wave travel, whereas longitudinal waves oscillate parallel to the direction of wave travel
Examples of transverse wave
- Water waves
- Electromagnetic (specific)
- Seismic S wave
Examples of longitudinal wave
- Sound
- Shock
- Seismic P wave
Define amplitude
Maximum displacement of oscillation from the equilibrium point
Define wavelength
Distance between 2 consecutive crests (on a transverse), or distance between 2 consecutive compressions (on a longitudinal)
Define time period
Time for one wave to pass a certain point
Define frequency
Number of waves that pass per unit time
Wave speed equation
Wave speed = wavelength x frequency
Wavelength equation
Wavelength = wave speed / frequency
Symbol for wave speed
v
Symbol for frequency
f
Law of waves
All waves transfer energy and information, without transferring matter
Frequency equation
Frequency = 1 / Time period
Time Period equation
Time period = 1 / frequency
Time period symbol
T
Define the doppler effect
The apparent change in frequency or wavelength of a wave for an observer moving relative to it’s source
Why do you hear a high then low pitch as a car approaches you?
- As the car moves towards you, the wavefronts bunch up and the wavelength decreases
- Speed of the car remains the same
- v = f (X) means wavelength decreases, and frequency increases for the same speed
- You hear a higher pitch
EM spectrum in increasing wavelength
- Gamma
- X-ray
- Ultraviolet
- Visible light
- Infrared
- Microwave
- Radio wave
EM spectrum in decreasing wavelength
- Radio wave
- Microwave
- Infrared
- Visible light
- Ultraviolet
- X-ray
- Gamma
Common features of EM waves
All travel at 3x10 8 m/s, can be reflected/refracted and can travel through a vacuum
Uses of Radio Wave
Broadcasting and communication
Uses of Microwave
Cooking and satellite transmissions
Uses of Infrared
Heaters and night vision equipment
Uses of visible light
Photography and optical fibres
Uses of Ultraviolet
Fluorescent lamps and tanning beds
Uses of X-rays
Observing the internal structures of objects, and can be used medically
Uses of gamma rays
Sterilising food and medical equipment
Dangers of radio waves
No known dangers
Dangers of microwaves
Internal heating of body tissues
Dangers of infrared
Skin burns
Dangers of visible light
Eye damage
Dangers of ultraviolet
Damage to surface cells and blindness
Dangers of x-rays
Cancer and mutation
Dangers of gamma rays
Cancer and mutation
Law of reflection
angle i = angle r
Ray diagram: Check list
- Draw a normal at 90 to where the incidence ray hits
- Arrow all rays
- Label all angles
- Label values of all angles
Define refraction
The bending of a wave and changing of direction, as it changes speed
What happens when a light goes from air to glass
- Light bends towards normal
- Speed and wavelength decrease
- Frequency remains the same
What happens when a light goes from glass to air
- Light bends away from normal
- Speed and wavelength increase
- Frequency remains the same
Refractive index equation
n = sin i / sin r
Symbol for refractive index
n
PRACTICAL: How to obtain a trace diagram for a light ray
- Place the block of plain paper, and draw around it using a pencil, ensuring it doesn;t move
- Allign the ray box so a single bean hits the block
- Mark it’s entry and exit with a pencil
- Join with a ruler
- Add arrows, normal and other measurements with a protractor
PRACTICAL: How to obtain refractive index of object
- Place the block of plain paper, and draw around it using a pencil, ensuring it doesn;t move
- Allign the ray box so a single bean hits the block
- Mark it’s entry and exit with a pencil
- Join with a ruler
- Add arrows, normal and other measurements with a protractor
- Measure angle i and r with a protractor
- Repeat with at least 4 angles
- Plot a sin i / sin r graph and the gradient = n
Conditions for T.I.F
- Ray must be moving from high refractive index to low refractive index
- Angle of incidence must be greater than the critical angle
Conditions for T.I.R
- Ray must be moving from high refractive index to low refractive index
- Angle of incidence must be greater than the critical angle
T.I.F is used in fibre optics. How a re fibre optics specialsied
Thin, and are made of a high refractive index material
Uses of fibre optics
- Communications (in cable TV and broadband)
- Endoscopes for medicine
What is the critical angle
Critical angle equals angle of incidence when the ange of refraction is 90
Critical angle equation
sin c = 1 / n
Symbol for critical angle
c
Human hearing range
20 - 20,000 Hz
What does pitch correlate to
Frequency
What does amplitude correlate to
Volume
PRACTICAL: How to find the speed of sound in air
- Make a noise heard over 100m like banging 2 wooden blocks together
- Use speed = distance / time
- Must have still air
- Repeat and average
- Stopwatch at zero and have clear visual signal
- Meaure time taken of seeing block hit, and when heard
- Factor in reaction time
How to calculate time period from an oscilloscope (and then frequency)
Multiply the time base by however many it takes for a complete wave to occupy it, then use F = 1/T equation
PRACTICAL: Obtain frequency from an oscilloscope
- Connect microphone to input channel and turn on for a steady trace
- Adjust time base, so there is a complete cycle on the screen
- Measure squares (time base) for a complete cycle
- Multiply number of squares by time ase, to find time period
- Use F = 1/T to get frequency
