Waves Flashcards
What do waves transfer?
waves transfer energy without transferring matter
What is displacement in a wave?
distance from rest position (of a particle)
What is amplitude?
the furthest distance a particle in a wave moves from its rest position
What is wavelength?
distance between successive crests or successive troughs
Define ‘wavelength’ in terms of particles.
distance between successive particles moving in phase
What are some examples of transverse waves?
water
all electromagnetic radiation
seismic S-waves (secondary)
What is time period T?
time for one complete oscillation of a particle
What is frequency?
number of oscillations per second
Formula for wave speed.
frequency x wavelength
What is the direction of vibration in a transverse wave?
perpendicular (right angle) to the direction of propagation
What is the direction of vibration in a longitudinal wave?
parallel to the direction of propagation
What are some examples of longitudinal waves?
sound waves
seismic P-waves (primary)
What causes wave refraction?
change of speed
What is refraction?
change in wave speed that results in a change of wave direction
What causes wave diffraction?
when waves go through a narrow gap or meet an obstacle
What causes LITTLE diffraction?
when the gap size is bigger than the wavelength
What causes A LOT of diffraction?
when the gap size is a similar size to the wavelength
What is diffraction?
the spreading out of waves through a gap or around an obstacle
How does wavelength affect diffraction at an edge/obstacle?
the bigger the wavelength, the more diffraction
when wavelength is small there is no diffraction (eg microwaves)
What happens when water waves go from deep to shallow water?
when they enter shallow water at an angle, they slow down an change direction
What happens to the frequency of the wave when it slows down?
does not change
What happens to the wavelength of the wave when it slows down?
wavelength decreases
what moves waves forward
transfer of kinetic energy
transverse waves
oscillation is perpendicular to direction of energy transfer (propagation)
examples of transverse waves
light, electromagnetic
longitudinal wave
direction of vibration is parallel to direction of energy transfer (propagation)
examples of longitudinal waves
sound
longitudinal waves have
compressions and rarefractions
wavelength in transverse
from crest to crest
What do waves do?
transfer energy from one place to another without transporting any matter
What is oscillation?
vibration repeated (side to side/back and forth)
motion about a fixed point
particle oscillation is at __ degrees to the wave direction
90
What is displacement?
distance from rest position (of a particle in a wave)
What is amplitude?
maximum displacement
What is wavelength?
distance between successive peaks or troughs
What are some examples of transverse waves?
water, springs, electromagnetic waves, seismic waves…
What is frequency?
number of oscillations per second
formula for frequency
1/time for one complete oscillation (T)ORnumber of oscillations/time taken
formula for wave speed
frequency X wavelength
What is a time period (T)?
time for one complete oscillation of a particle
What is the formula for speed?
distance/time
In what direction do wave particles oscillate?
parallel to direction of wave travel
What is a compression?
higher particle density (greater pressure than Atmospheric)
What is a rarefaction?
lower particle density (lower pressure than Atmospheric)
What is wavelength in a longitudinal wave?
distance between successive rarefactions or compressionsOR distance between successive particles oscillating in place
What are some examples of longitudinal waves?
sound, springs, seismic p-waves (primary)
Name 4 properties of images in plane mirrors.
- upright
- virtual (real light rays do not come together)
- laterally inverted
- same size as object
- image is same perpendicular distance behind the mirror as the object is in front
Is an image in a plane mirror real or virtual?
virtual (real light rays do not come together)
What happens to light as it enters a different medium?
changes speed and direction
When light goes from a LESS dense to a MORE dense medium, what happens to the refraction?
refraction is towards the normal
i>r
When light goes from a MORE dense to a LESS dense medium, what happens to the refraction?
refraction is away from the normal
i<r
What happens in refraction when the angle of incidence is 0?
no refraction
What is the critical angle?
angle between incident ray and normal, when the refracted ray is parallel to mediums surface
What is refractive index (n)?
the ratio of the speeds of a wave in two different regions
What causes total internal reflection?
when angle of incidence is greater than the critical angle and when wave speeds up after crossing boundary
How does an optic fibre work in telecommunication?
used to transmit optical pulses over long distances
short pulse of light produced at one end, travels along fibre, if it encounters a boundary it totally internally reflects
What are properties of an image formed when object is beyond 2F?
real
upside down (inverted)
diminished
What are properties of an image formed when object is in between F and 2F?
real
upside down (inverted)
magnified
What are properties of an image formed when object is in between F and the lens?
virtual
upright
magnified
Formula for magnification
img height/object height or /img distance/object distance
How is a virtual image formed?
when diverging rays are extrapolated (extended) backwards, not forming a visible screen projection
How can short-sightedness be corrected?
adding a diverging lens in front of the cornea
How can long-sightedness be corrected?
adding a converging lens in front of the cornea
What is the focal length?
distance along principal axis from centre of lens to principal focus
What is the focal point/principal focus?
light parallel to principal axis incident on the lens is refracted and meet at the focal point
What is the principal axis?
the line that passes through both the centre of the lens surfaces and their centres of curvature
What is monochromatic?
visible light of a single frequency
order of rainbow (visible spectrum)
ROY G BIV
Which colour is refracted the least? Which one the most?
red the least
violet the most
What is the speed of red light compared to the others? How does this affect refraction?
faster
refracts less
What is the speed of violet light compared to the others? How does this affect refraction?
slower
refracts more
In glass, what are the relative wavelengths of red and violet light?
wavelength of red is bigger than wavelength of violet
State properties of red light.
- faster
- refracts less
- greater wavelength
State properties of violet light.
- slower
- refracts more
- smaller wavelength
State the main regions of the electromagnetic spectrum in order of wavelength, from longer to shorter.
radio waves
micro waves
infrared
visible light
ultra violet
x rays
gamma rays
State the main regions of the electromagnetic spectrum in order of frequency, from low to high.
radio waves
micro waves
infrared
visible light
ultra violet
x rays
gamma rays
How is the wavelength and the frequency in radio waves?
large wavelength
low frequency
How is the wavelength and the frequency in gamma rays?
short wavelength
high frequency
All electromagnetic waves travel at the ______ speed in a vacuum.
same
State typical uses of radio waves.
radio and television transmissions
astronomy
radio frequency identification
State typical uses of microwaves.
satellite television
mobile phones
microwave ovens
State typical uses of infrared.
electric grills
short range communications (eg TV control remotes)
intruder alarms
thermal imaging
optical fibres
State typical uses of visible light.
vision
photography
illumination
State typical uses of ultraviolet.
security marking
detecting fake bank notes
sterilising water
State typical uses of X-rays.
medical scanning
security scanners
State typical uses of gamma rays.
sterilising food
sterilising medical equipment
detecting and treating cancer
State typical uses of gamma rays.
sterilising food
sterilising medical equipment
detecting and treating cancer
What are harmful effects on people of excessive exposure to microwaves?
internal heating of body cells
What are harmful effects on people of excessive exposure to infrared?
skin burns
What are harmful effects on people of excessive exposure to ultraviolet?
damage to surface cells and eyes, leading to skin cancer/eye conditions
What are harmful effects on people of excessive exposure to X-rays and gamma rays?
mutation or damage to cells in the body
What is the speed of electromagnetic waves in a vacuum?
3 x 10ˆ8 m/s
What is the speed of electromagnetic waves in air?
approximately same as vacuum
What type of electromagnetic radiation is used for communication with artificial satellites?
microwaves
What do satellite phones use?
some use low orbit artificial satellites
some use geostationary satellites
What does direct broadcast satellite television use?
geostationary satellites
What are geostationary satellites used for?
some satellite phones
satellite television
What are low orbit artificial satellites used for?
some satellite phones
What do mobile phones and wireless internet use?
microwaves
Why are microwaves used for mobile phones and wireless internet?
- can penetrate some walls
- only require a short aerial (antenna) for transmission and reception
What does bluetooth use?
radio waves
Why are radio waves used for bluetooth?
radio waves pass through walls (but signal is weakened if this happens)
What are uses of optical fibres?
cable television
high-speed broadband
Why is glass used in optical fibres?
it is transparent to both visible and some infrared light
What two waves can carry high rates of data (optical fibre)?
visible light
some infrared
What is an analogue signal?
signal can be any level within a range and varies continuously
What is a digital signal?
signal has fixed values, information is sent in pulses of fixed duration (eg binary)
What are benefits of digital signaling?
- increased rate of transmission of data
- increased range due to accurate signal regeneration
Why does digital signalling increase range?
because of accurate signal regeneration
what is angle of incidence?
angle between normal and ray of light
what is angle of reflection?
angle between reflected ray and normal
what is refraction
when waves change speed and direction when passing from one medium to another
when light travels from a less dense medium to another what happens
it bends towards the normal
lens can be
diverging or converging
diverging lens (mari ignora)
espalha dps de passar
converging lens (mari ignora)
junta dps de passar
when top of an image is formed below the optical axis, the image is
inverted
when image is formed by extension of light rays, the image is
virtual
what is principal focus
point where rays of light travelling parallel to axis meet and converge
what is focal length
distance between centre os lens and focal point
how is long sight corrected
converging lens
how is short sight corrected
diverging lens
what is dispersion
splitting of white light through a glass prism into each colour
order of colours from longest to shortest wavelength
red
orange
yellow
green
blue
indigo
violet
order of colours from shortest to longest frequence
red
orange
yellow
green
blue
indigo
violet
what do analogue signals have
continuous electrical signals
what do digital signals have
non-continuous electrical signals
is sound transmitted as analogue or digital
both :)
How is sound produced?
vibrating sources
Are sound waves transverse or longitudinal?
longitudinal
What is the approximate range of frequencies audible to humans?
20 Hz to 20 000 Hz
Is a medium necessary or not to transmit sound waves?
yes
What is the speed of sound in air?
approximately 330-350 m/s
Which state of matter does sound travel faster in?
solids
Which state of matter does sound travel slower in?
gases
What is an echo?
reflection of sound waves
What is ultrasound?
sound with a frequency higher than 20 kHz
What are uses of ultrasound?
non-destructive testing of materials
medical scanning of soft tissue
sonar
What are compressions?
regions of air (or another material) where particles are compressed closer together than normal due to the passing of a sound wave
What are rarefactions?
regions of air (or another material) where particles are spread out further than normal due to the passing of a sound wave
what happens to the angle of incidence in a reflection? (equation)
angle of incidence = angle of reflection
what is the normal
line drawn perpendicular to a surface from which angles of incidence, reflection and refraction are measured.
what is the angle of incidence
angle between the incident ray and the normal to the mirror
what is the angle of reflection
angle between the reflected ray and the normal in the mirror
equation for refractive index
n = sin i / sin r
what is refractive index
ratio of the speeds of a wave in two different regions
what is snell’s law
n = sin i / sin r
What is the critical angle?
The largest angle of incidence which allows light to leave a material. Above this angle the light will be totally internally reflected.
equation for critical angle
n = 1 / sin c
what is internal reflection
When light moves across a boundary between materials some of it is reflected back from the boundary.
what is total internal reflection
When light is perfectly reflected as its reaches a boundary. The effect only happens if the angle of incidence is above the critical angle.
colors are essentially
rays of light with different frequencies
visible light of a single frequency is
monochromatic
Uses of LEO satellites
some for spying or observing weather
many are now part of phone networks or the internet
Are geostationary satellites suitable for fast internet?
no, as the signals need to travel a large distance, there can be a delay in communications
