waves- topic 3 Flashcards
waves
Oscillations in a medium that transfer energy not matter
wave motion
Wave motion is the transfer of energy from one point to another. We can demonstrate this by hanging an object on a stretched string and then sending a pulse down the string (by moving it up and down quickly like a wave)
oscillation
vibration repeated side to side or back and forth motion in a fixed point
displacement
distance from rest position (0 displacement)
amplitude (A)
a wave is its maximum distance from the equilibrium.
maximum displacement
from x axis to wave peak (A)
wavelength
distance between successive crests or successive troughs
crest (peaks) vs troughs
crests=The peak of a wave. The part of a wave at maximum amplitude.
troughs=The bottom of a wave. The point with minimum amplitude.
frequency
the number of waves produced each second. It is denoted by the letter f and is measured in hertz (Hz).
wavefront
an imaginary surface that we draw to represent the vibrating part of a wave
wave speed
the distance travelled by a wave each second.
frequency * wavelength
transverse waves
the particle oscillates perpendicular (at right angles) to the direction of propagation of the wave
electromagnetic radiation, water waves and
seismic S-waves
troughs and crests
longitudinal waves
the oscillation of the particles is parallel (in the same direction) to the direction of propagation of the wave
sound waves
and seismic P-waves (primary)
rarefactions and compressions
reflection of a wave
a wave ‘bounces’ off a boundary
changes direction
wave speed, frequency and wavelength does not change
rarefraction of a wave
a wave moves from one medium to another
change in speed caused by movmeent form one material to the other causes a change in wavelength, can also cause change in direction in which wave is travelling depending on angle wavefront reaches boundary
If the wavefronts are parallel to the boundary, the wave will just change speed
no change in direction
diffraction
a wave spreads as it moves through a gap. curved pattern
incident ray
The path of a wave which travels from the source. reaches boundary
reflected wave
The path of a wave which has reflected from a surface. hit boundary and bounced off
what happens if wavefront is parallel to surface when it hits
wavefront will be reflected back in the direction it came from
what happens when waves travel from deep to shallow if not parallel to block
waves slow down, due to this frequency does not change, and wavelength decreases
direction of travel will change towards the normal. angle of rarefaction is smaller than incidence wave
what are two ways to increase diffraction
decrease size of the gap
increase wavelength of wave
A gap width similar to the wavelength of the waves passing through causes a lot of spreading
Describe how wavelength affects diffraction at an
edge
this amount of diffraction increases as the wavelength of the wave increases. Waves with long wavelengths diffract more than waves with short wavelengths.
what diffracts more and why? sound or light waves through an edge
As sound waves have much longer wavelength than light waves they are much more strongly diffracted by edges. This allows sound waves to spread around corners in a way that is not possible for light.
describe refraction from deep water to shallow water at an angle
wave travelling through deep water is faster, when it enters shallow surface, it slows down and this causes a change i direciton, when waves slow down wavelengths decrease, angle of incidence is bigger than angle of rearefraction, getts smaller with bigger angle
what happens when a wave is travlleing from deep water to shallow water but is parallel to boundary
no change in direction only change in speed goes from fast to slow, wavelengths decrease
what is light
electromagnetic transverse wave
what is the law of reflection
i=r
what are the properties of images in a plane mirror
image is uprights, image is virtual, laterally inverted (right side of object is left side of image), same size, image same perpendicular distance behind mirror as object is infront
describe rarefraction of light
when light enters a different medium it changes speed and direction, same speed in same medium
describe rarefraction of light from a less dense medium to a more dense
eg. air- water or air- glass
incidence ray is bigger than refracted one refraction towards normal speed decreases, frequency is constant, wavelength decreases
describe rarefraction of light from a more dense medium to a less dense
eg. water- air or glass- air
incidence ray is smaller than refracted one, refraction away from normal, speed increases, freuqunecy is constant, wavelenth increases
Describe an experiment to show refraction of light by transparent blocks of different shapes
use a raybox to point light at an angle to a differnet medium, eg, transparnet block trace light rays by markey 3 crosses per ray and connecting with a ruler
use a protractor to measure angles
large angles have less measurment errors
or use pins by looking at their bases, and then trace their paths, repeat both expirments 5 times and calculate average refractive index (n)
describe refraction with ray going 90 degrees to boundary
no refraction
what are formulas for refractive indx
n= sini/sinr
n=1/sinc
n=v1/v2
n=wavelengthfrequnecy/ wavelength2frequency2
define n
refractive index, ratio of speeds of a wave in two different regions
what is meant by critical angle
angle of incidence that results in an angle of refraction of 90 degrees, therefore at boundary, no “seen”refraction”only reflection
when does total internal reflection take place
when light moves from more dense to less dense medium angle of incidnce= critical angle refraction= 90 degrees
angle of incidence is called critical angle
what are optical fibres why are they used?
in optical fibres only total internal reflection occurs, i is greater than critical angle used for telecommunications- carry binary digit code as a series of infrared or visible light signals , carry more info than electrical signlas and are more secure and harder to “tap”
made from glass which is much cheaper can carry several different signals down fibre at same time
used in endoscopes- bundle of optical fibre fed into patients stomach allows doctor to look inside
principal focus
he point where rays of light travelling parallel to the principal axis intersect the principal axis and converge (F)
focal length
distance between the centre of the lens and the focal point.
principal axis
The horizontal line passing through the optical centre of the lens
describe ray diagram and caracteristics of image beyond 2F
image is real
upside down (inverted)
smaller than object( diminuished)
describe ray diagram and caracteristics of image at 2F
real
inverted
same size as object
describe ray diagram and caracteristics of image between F and 2F
real
inverted
magnified
magnificaton formula
image hiehgt/ object hiehgt
image distance/object distance
describe ray diagram and caracteristics of image inbetween F and lens
virtual
magnified
upright
(image to the left of the object)
describe a virtual image
formed when diverging rays are extrapolated backwards and does not form a visible projection on a screen
describe how short sightedness is fixed
diverging lens is used
diverging lens forms a virtual image of the distance object, closer to the eye
light rays will diverge when passing through lens and form focused image on retina
describe short sightedness
unfocused image formed on retina, lens is too powerful
decribe long sightedness
unclear unfocussed image formed on retina, eyelens is too weak or eyeball too short
describe correcting long sightedness
use convergins lens
forms a virtual image further away from object
converges light rays and a focussed image is formed on retina
describe dispersion
dispersion is when white light which consists of all the colours travelling in same speed (3 *10ˆ8) hit a glass prism and because of their differnet wavelengths, travel at different speeds and undergo refraction
what is order of colours from less refraction to more
red,orange, yellow, green, blue, indigo,violet
what is meant by monochromatic
visible light of a single frequency
explain red light and its refraction
red light has a greater speed in glass, lower freuqunecy and bigger wavelength, refracts less
explain blue light and its refraction
has a smaller speed in glass, higher freuqunecy and smaller wavelength, refracts more
what is the order of electromagnetic spectrum and trends
(rich men in vegas use expensive girls)
radio waves, microwaves, infrared, visible( red, violet), ultraviolet, xrays, gamma
from longest wavelength to shortest
from smaller frequency to bigger
describe some properties of electromagnetic waves
all transverse waves
travel at same speed in a vaccum ( 3* 10ˆ8)
approximately same in air
describe use of radio waves
radio and television
transmissions, astronomy, radio frequency
identification (RFID)
describe use of microwavs
satellite television, mobile
phones (cell phones), microwave ovens
describe use of infrared
electric grills, short range
communications such as remote controllers
for televisions, intruder alarms, thermal
imaging, optical fibres
describe use of visible light
vision, photography, illumination
describe use of ultraviolet
security marking, detecting fake
bank notes, sterilising water
describe use of x rays
medical scanning, security scanners
describe use of gamma
sterilising food and medical
equipment, detection of cancer and its
treatment
describe harm of microwaves
internal heating of body cells
describe harm of infrared
skin burns
describe harm of ultraviolet
damage surface cells and eyes, skin cancer eye conditions
describe harm of x-rays and gamma
cell mutation and damage to cells
describe mobile phones and how they rely on electromagnetic radiation
use microwaves because microwaves cam penetrate some walls and only require short aerial for transmission and reception
describe bluetooth and how they rely on electromagnetic radiation
uses radio waves because radio waves pass throguh wals but signal is weakened doing so, and with distance from device
describe optical fibres and how they rely on electromagnetic radiation
uses visible light and infrared, for cable tv and high speed broadband because glass is transparent to visible light and some infrare, visible light and short wavelength infrared can carry hight rates of data
communication with artificial
satellites
uses microwaves because it can pass throguh earths atmosphere and have been used to communicate to artifical satellites
describe low orbit satellites
satellite phones use them, data sent very fast
describe high orbit or geostationary setellites
some satellite phones and direct broadcast satellite tv, above equator
analogue signals
continuoes value can be single or mixed frequency
digital signals
digital can only have precise values binary digital value- 0 or 1
not continuos wave
sound can be transmitted as
digital or analouge signals
Explain the benefits of digital signaling
increased range due to accurate signal
regeneration- data can be sent further and have a greater range they by regenerated more accurately than analogue
send more info in shorter space of time- greater rate of transmission of data
digital signals are less affected by noise
Describe the production of sound
whenever two materials rub together or a vibrating source, all longitudinal
what is frequency in sound
number of oscillations of a particles on the wave per sec
human audible frequency range
20- 20000 Hz
what is needed to transmit sound
a medium, doenst flow/ radiate energy through a vaccum
speed of sound in air
330- 350 m/s
compression
a region of high particle density
rarefraction
a region of low particle density
what medium does sound waves travel the fastest and why
solids than in liquids and faster in liquids than in gases
because in solids particles are closer together and oscillate strong forces between molecules
speed of sound in solid
5000 m/s
speed of sound in liquid
1500 m/s
Describe a method involving a measurement of
distance and time for determining the speed of
sound in air
use a gun and measure time taken to hear, then divide distance from person with gun to time taken to listen
greater the amplitude (sound)
greater loudness of a sound
greater freuqunecy
hgiher the pitch, smaller wave length, waves closer togethr
what is an echo
reflection of sound waves
formula used to calculate echos
2d= sound speed * time taken
ultrasound
sound of frequnecy above 20KHz
what are uses of ultrasound in nondestructive testing of materials
ultrasound sent through metal or plastic or other materials, crack will reflect ultrasound eave, good matrial will not reflect, material is tested without cutting it open
what are uses of ultrasound in medical scanning of soft tissue
ultrasound reflects off human tissue of differnet densities, doctor uses transmitter to send ultrasound which reflects off tissue and tected by receiver, comp can calculate depth of tissue
eg. imaging fetus
safe and non ionising
ultrasound travels at differnet speeds in different types of tissue, greater the density of tissue grater speed, faster in muscle slower in fat
