P2: Wave motion, Sound waves, Electromagnetic waves Flashcards
Nemonic for remembering electromegnetic spectrum
Rich Men Invent Very Unusual Xray Guns
In order of decreasing wavelength (i.e. largest to smallest wavelength)
- Radiowaves
- Microwaves
- Infrared waves
- Visible light
- ultraviolet waves
- Xrays
- Gamma Rays
What is a longitudinal wave?
A wave in which the oscillations or vibration are parallel to the direction the wave is travelling.
What is a transverse wave?
One in which the oscillations or vibrations take place at right angles to the direction the wave is traveling.
points are said to be in phase in a progressive wave when (1)___________________ , which means the distance between them along the direction of propagation is (2) _____________ Points that are in phase have the same (3)_______________ (4)_______________ and (5)______________ in their vibrations.
- they are at the same corresponding position
- the distance between them along the direction of propagation is 0λ, 1λ, 2λ etc.
- direction
- displacement
- speed
points in a progressive wave are said to be out of phase if (1)____________ and so the do not have the same (2)____________ (3)_____________ or (4)______________________.
- they are not at the same corresponding position in the wave
- direction
- speed
- displacement
what is a pluse?
a single disturbance that propagates from one point to another
What are electromagnetic waves classed as?
Transverse waves
What are sound waves classed as?
Longitudinal
What is the amplitude of a wave?
the maximum displacement of the vibration or oscilation form its mean position
What is a wave?
A mean of transferring energy from place to place.
What is the wavelength of a wave?
The distance from a particular point on a wave and the same point on the next wave.
What is the frequency of a wave?
The number of waves produced each second. Measured in hertz.
What is the relationship between speed, frequency and the wavelength of a wave?
Wave speed = frequency x wavelength
What is the relationship between frequency and time period?
Frequency = 1/time period f = 1/T
What is T measured in?
Seconds
Why do waves travel more slowly in shallower water?
As a wave enters a region of shallower water the wavelength is decreased, yet the frequency remains the same. In deeper water their wavelength increases.
What is refraction?
When a change in speed causes a change in direction of travel at the boundary eg water waves bend towards the normal when travelling from deep to shallow water
What is diffraction?
The spreading out of waves as they pass through a small gap.
Give the EM spectrum from low to high frequency
Radiowaves, microwaves, infrared, visible, ultraviolet, x-rays, gamma rays
Uses of ultraviolet waves (UV)
The main use of UV radiation is FLUORESCENCE
- flourescent light bulbs
- -highlighters
- -security markers on money
- -forensics, eg identifying body fluids such as sperm and blood
- -teeth whitening
- -detergents have fluoresent substances that make clothes appear brigher.
What is flourescence?
the process where an object absorbs UV radiation and then emits visible light in return. i.e the object converts invisible UV light to visible light
Uses of X-rays?
- Medical imaging
- Scanning of passengers and luggage at airport security checkpoints
- Investigating the structure of crystals
Uses of gamma radiation
- Sterilizing surgical equipment
- cancer treatment(radiotherapy)
- gamma imaging such as looking at engine parts for breaks.
Uses of microwaves
- cooking using microwave ovens
- satellite transmissions
Uses of infrared waves (infrared radiation)
- Night vision equipment and infrared cameras
- Cooking equipment such as toasters and heat ovens that use heat to cook food
- remote controls
- Used in fibre optic cables to transmit information
What are the risks of UV?
Damage to surface cells (can lead to skin cancer) and blindless
Uses of visible light?
- Optical fibres in telecommunications
- photography
What are the risks of infrared?
Skin burns
What are the risks of microwaves?
Internal heating of body tissue
What are the risks of gamma radiation?
Can cause cells to mutate and cause cancer
What are sound waves?
Longitudinal waves which can be reflected, refracted and diffracted
What property of electromagnetic waves makes then good for communication?
They can travel long distances and travel fast
points are said to be in antiphase in a progressive wave when (1)___________________ , which means the distance between them along the direction of propagation is (2) _____________ Points that are in phase have the same (3)_______________ (4)_______________ and (5)______________ in their vibrations.
- the distance between them along the direction of propagation is ½λ, 1½λ, 2½λ etc.
- direction
- displacement
- speed
which particles are
- in phase
- in antiphase
- in phase: (A, E), (C, G), (B, F), (D, H)
- (A,C), (C, E), (E, G), (B, D), (D, F), (F, H)
Identify how these groups of points are related
- A, C
- B, F
- C, E,
- C, F, H
- E, F, G
- C, H
- A, G
- D, H
- A, F
- B, D
- antiphase
- in phase
- antiphase
- out of phase
- out of phase
- out of phase
- antiphase
- in phase
- out of phase
- antiphase
the number of complete vibrations per second of a wave is known as its ____________
frequency
this wave parameter, its____________, is the time for one complete vibration
Period
symbol for period
T
symbol for frequency
f
symbol for wavelength
λ
symbol for refractive index
η
The (1)_____________is a line perpendular to the propagation of a wave on which all points are (2)______________. Wavefronts are are generally taken througth the (3)___________ of transverse wave and throught the (4)___________ of longitudinal waves.
- wavefront
- in phase
- crests
- compressions
the (1) ___________ of a wave is the rate at which the wavefront of a wave is propagated. The formulafor wave speed is (2)_____________ and dependson (3)_______________
- speed
- v = λf
- medium in which the wave is travelling
what is the relationship between the frequency and Period(T) of a wave?
T = 1/f
How is the frequency and period of a wave related?
Period is inversely proportional to its frequency
which of these affect the speed of a wave?
- density of the media in which it travels
- its frequency
- its wavelength
- its period
- the angle at which the wave travels
- only - density of the media
these change when a wave passes from one media to another
- its speed, v
- wavelength, λ
- angle (except if incident wave is at 90 degrees)
these do not change when a wave passes from one medium to another
Period and Frequency
when an electromagnetic wave reaches the earth from the sun, what properties of the wave will change when it passes throught the earth’s atmosphere? (1)_________________ and (2)______________
Its speed will (3) _____________ and its wavelength will (4)______________
- speed
- wavelength
- decrease
- decrease
if the speed of light doubles when it passes from a (1)_______________ to a (2)______________ medium, then is wavelegth and sinθ will (3)_____________ but its frequency will (4)____________
- more dense
- less dense
- double
- remain unchanged
what is the Hertz (Hz)
unit of frequency
what is the expanded form of the following?
- 10 MHz
- 2.5 kHz
- 5 GHz
- 10 000000 Hertz
- 2500 Hertz
- 5000000000 Hertz
this is the only thing that affects the frequency of a wave
its source
The general properties of electromagnetic waves
- transverse waves
- all have the same speed in a vaccum
- (3x108ms-1)
- they travel in a vacuum
- have electrical and magnetic fields
- they can reflect
- they refract
- the diffract
- they exhibit interference
- they transfer energy
what is the electromagnetic spectrum?
arranges electromagnetic waves acccording to their frequency and wavelengths
How does a microwave work?
- The water molecules in the food absorb the microwaves. 2. Therefore the water particles have more energy and so mover faster and get excited, producing heat and so the food becomes heated.
How can you protect yourself from UV light?
- Sunscreen with UV filters
- Ozone in the Earth’s atmosphere absorbs large quantities of the Sun’s UV radiation, and protects us
How can you protect yourself from X-rays (and Gamma rays)?
- -Stand behind lead screens or wear protective clothing (lead shield as too dense for x-rays)
- -Gamma rays are only aimed carefully so that they cross at the exact location of the cancerous cells,
- -Radioactive sources of gamma rays should be kept in lead-lined boxes when not in use
- -When people are exposed to gamma rays e,g, in medical treatment the exposure time should be as short as possible
What does an optical fibre do?
Carries data over long distances as pulses of light
How is the danger of EM radiation related to frequency?
- The effects of EM radiation depend on its frequency. The higher the frequency of EM radiation, the more energy it has and generally the more harmful it can be
- In general waves with lower frequencies (like radio waves, which are harmless as far as we know) are less harmful than high frequency waves like X-rays and Gamma Rays
What is diffraction?
The spread of waves when passing through a gap or round the edge of an obstacle.
How does diffraction effect ultrasonic imaging?
If the transmitter is too narrow, the waves spread out making the image unclear.
What is the range of human hearing?
20-20,000 Hz
What are sound waves?
Vibrations that travel through a medium.
how is are the pitch and frequency of sound related:
greater frequency produces higher pitch
What are echoes?
Sound waves reflected from a smooth, hard surface.
how are the loudness and amplitude of a sound wave related
greater amplitude gives higher volume
what kind of wave is sound?
longitudinal wave
why does the speed of sound increase in the following order?
Solid > liquid > gas
the closer the packing of the particle and rigidity of the bonds allow vibrations to travel more readilty
How does air temperature affect the speed of sound?
The warmer the air, the greater the speed of sound.
Where does sound refraction take place in air?
The boundaries between layers of air at different temperatures.
Which way does sound reflect in the day and why?
In daytime, sound refracts upwards because the air near the ground is warmer than the air higher up.
why is it that sound does not travel in a vacuum?
vacuum has no particles to pass on the vibrations
this property of sound waves is affected by frequency
pitch
this property of sound is affected by it amplitude
its loudness or volume
in order for humas to hear a sound wave, its (1)_______________ has to be between (2)_________ Hz and (3)_________kHz
- frequency
- 20
- 20
sound wave is ultrasound if its (1)______________is above (2)_______kHz and is (3)__________ if below (4) 20 Hz
- frequency
- 20
- infrasound
uses of ultrasound
- measuring distance
- communicating
- diagnostic imaging in medicine
- testing solid materials for flaws
- cleaning of small object such as electronic components
a simple method of estimating the speed of sound in air
using echoes
how to use echoes to measure the speed of sound in air
- two persons A and B stand 50m away form a tall hard and smooth vetical wall
- person A claps 2 blocks of wood 20 times, each time clap coinciding with the echo.
- Person B will record the time it takesto clap 20 times.
- The speed is calculated using the total distance (50 x2)m/ total time
what is the speed of sound in air?
approx. 330m/s
using sound to estimate how far a thunder storm is
(sound travels at about 330m/s)
- when you see a lightning flash start the timer
- record the amount time it took to hear the thunder in seconds
- use the equation v = d/t, transposing as necessary to find d, the distance.
how to use echoes to determine the depth of water.
- A transmitter emits the sound and timer started automatically
- a receiver detects the reflected pulses and records the time
- a computer calculates the depth of the water from the equation: v = 2x/t where x is the distance to determine
How can you measure the speed of sound in air using echoes?
- 1) Stand 50m away from a large, blank wall and clap or bang two pieces of wood together and listen for the echo
- Set up a rhythm of claps so that the echo comes exactly between two claps
- Ask a friend to time 20 claps - during this time the sound has travelled 2000m (to the wall and back 20 times)
- Repeat the experiment to get an average time and to make the experiment more reliable
- You now divide the distance (2000m) by the average time.
NB Control variables that are necessary for this to work: still air; set stopwatch to zero before experiment
