Waves New Flashcards
transverse wave
Waves that vibrate or oscillate perpendicular to the direction of energy transfer
what do transverse waves transfer
-energy but not the particles of the medium
what can mechanical transverse waves travel through
in solids or on the surfaces of liquids but not through liquids or gases
what can electromagnetic waves move in and what type of wave are they
-transverse
-can move in solids, liquids, gases and in a vacuum
highest point above the rest position of a transverse wave
peak or crest
lowest points below the rest position of a transverse wave
trough
examples of transverse waves
-ripples on the surface of water
-electromagnetic waves
-S-waves
longitudinal waves
Waves where the points along its length vibrate parallel to the direction of energy transfer
what state of matter can longitudinal waves travel in
can: solids, liquids and gases
cannot: vacuum as there are no particles
what do longitudinal waves transfer
-energy but not the particles of the medium
what are the two features of a longitudinal waves diagram
-compressions (when the particles are close together
-rarefactions, when the particles are spaced apart
examples of longitudinal waves
-sound waves
-P-waves
what is the amplitude
Amplitude is the maximum or minimum displacement from the undisturbed position
what is the wavelength
The distance from one point on the wave to the same point on the next wave
how can you measure wavelength in transverse and longitudinal waves
-wavelength can be measured from one peak to the next peak in a transverse
-wavelength can be measured from the centre of one compression to the centre of the next in longitudinal waves
what is the frequency
The number of waves passing a point in a second
what do waves with a higher frequency transfer in terms of energy
transfer a higher amount of energy
what is the time period
The time taken for a single wave to pass a point
equation linking frequency and time priod
f = 1/t
equation linking wave speed, frequency and wavelength
wave speed = frequency x wavelength
doppler effect
The apparent change in observed wavelength and frequency of a wave emitted by a moving source relative to an observer
mark scheme for doppler effect question
- doppler effect
- object is the source of the waves
- wavefronts are closer together
- wavelength decreases
- speed of waves stays the same
- frequency increases
list of EM waves in order of frequency(low to high)
- radio
- microwave
- infrared
- visible
- ultraviolet
- x-ray
- gamma ray
how does the wavelength, frequency and speed of EM waves from radio to gamma ray
-wavelength decreases
-speed stays the same(travel at the same speed in free space)
-frequency increases
how does the wavelength of visible light change the colour
-longer wavelength = red
-shorter wavelength = violet
in the list of EM left to right, red first violet last
radio wave use
broadcasting and communications
Microwaves use
Cooking and satellite transmissions
Infrared use
Heaters and night vision equipment
Visible light
Optical fibres and photography
Ultraviolet
Fluorescent lamps
X-rays
Observing the internal structure of objects and materials, including medical applications
Gamma rays use
Sterilising food and medical equipment
dangers of radio waves
the human body temperature can rise up by 0.2C
dangers of microwaves
can cause internal heating of body tissues
dangers of infrared
infrared radiation is felt as heat and causes skin to burn
dangers of visible light
visible light from a laser which is very intense can damage the retina at the back of the eye
dangers of ultraviolet
ultraviolet can damage skin cells and lead to skin cancer and damage the eyes, it can cause skin to age prematurely
dangers of X-rays
X-rays damage cells inside the body. They can damage the genetic material of a cell, the DNA. This can lead to cancer.
dangers of gamma rays
gamma rays also damage the genetic material of a cell, the DNA. This can lead to cell death and cancer.
how do microwave ovens prevent microwaves escaping
-metal walls and metal grid in the glass door
how to protect against infrared
-protective clothing such as gloves and prevent skin from feeling the heat
-how to protect against ultraviolet
-wearing sunglasses that absorb UV. sunscreen also absorbs it and prevents it from damaging the skin
gamma and x-rays protection
-doctors leave room during x-rays
-radiographers wear radiation badges to measure exposure
what type of waves are light and sound
-light: transverse
-sound: longitudinal
what does a higher amplitude mean in sound waves
-louder sound
what does a higher frequency mean in sound waves
higher pitch sound
when does reflection occur
A wave hits a boundary between two media and does not pass through, but instead stays in the original medium
when does refraction occur
A wave passes a boundary between two different transparent media and undergoes a change in direction
law of reflection
angle of incidence = angle of reflection
what is the normal
-a line at 90 degrees to the boundary
angle of incidence
angle of the wave approaching the boundary
angle of reflection
angle of the wave leaving the boundary
how does light bend from less dense to more dense medium
light bends towards the normal
why is there a change in direction of light when travelling in different substances
-when light passes into a denser substance the rays will slow down, and bend towards the normal
how does the frequency, speed and wavelength of waves change after a wave enters a medium with a different refractive index
-frequency stays the same
-speed and wavelength changes
method to investigate refractions
- Place glass block on a sheet of paper, and draw around the rectangular perspex block using a pencil
- Switch on the ray box and direct a beam of light at the side face of the block
3.mark on the paper: a point on the ray close to the ray box, the point where the ray enters the block, the point where the ray exits the block and the point on the exit light ray about 5cm away from the block - draw a dashed line to the outline of the block where the points are
- remove the block and join the points marked with three straight lines
6.replace the block within its outline and repeat the process for a ray striking the block at a different angle
snell’s law
n2/n1 = sin(i)/sin(r)
equation for refractive index
n = speed of light in a vacuum/speed of light in material(no units)
method to investigate snell’s law
same experiment as earlier, but plot sin i/sinr, sini = y axis. Gradient = n
what it total internal reflection
-when light reflected of a less dense medium when moving from a denser medium, and does not refract
when does total internal reflection happen
-the angle of incidence is greater than the critical angle and the incident material is dense than than the second material
method to measure the speed of sound in air
- use a trundle wheel to measure a distance of 100m between two people
- one of the people should have two wooden blocks, which they will bang together above their head to generate sound waves
3.the second person should have a stopwatch which they start when they see the first person banging the blocks together and stop when they hear the sound - This should be repeated several times and an average taken for the time travelled by the sound waves
- repeat for various distances
what is an oscilloscope
a device that can be used to study a rapidly changing signal e.g. sound wave or alternating current
what is the time base
like the x-axis, used to measure the time period of the wave in an oscilloscope
method to measure the frequency of a sound wave using an oscilloscope
- Connect the microphone to the oscilloscope
- Test the microphone displays a signal by humming
- Adjust the time base of the oscilloscope until the signal fits on the screen - ensure that multiple complete waves can be seen
- Strike the tuning fork on the edge of a hard surface to generate sound waves of a pure frequency
- Hold the tuning fork near to the microphone and observe the sound wave on the oscilloscope screen
- Freeze the image on the oscilloscope screen, or take a picture of it
- Measure and record the time period of the wave signal on the screen by counting the number of divisions for one complete wave cycle
8.Repeat steps 4-6 for a variety of tuning forks
range of human hearing
20Hz-20,000Hz
P waves
-longitudinal
-fast
-can travel through solids and liquids
S waves
-transverse
-slow
can only travel through solids
Equation relating refractive index and critical angle
n2/n1 = 1/sin(c)
c = critical angle
Equation relating refractive index of two medium and speed of waves in the two medium
n1/n2 = v1/v2
