Topic 6 - Waves Flashcards
Describe transverse waves
The vibrations are perpendicular to the direction of energy transfer
e.g water waves
Describe longitudinal
The vibrations are parallel to the direction of energy transfer
e.g sound waves
Define time period
the time taken for a particle to complete one vibrational cycle
Define frequency
the number of complete waves every second (measured in hertz)
Time period =
1 / frequency
Define wave speed
the speed at which energy is being transferred
Wave speed =
frequency x wavelength
Describe how you would use a ripple tank to measure the speed of waves
- set up the ripple tank, put a large sheet of card under the tank on the floor and pour about 5mm of water into the tank
- put the wooden rod so it just touches the surface of the water
- switch on the overhead lamp and motor and adjust so the waves are low frequency and you can see it clearly on the card
- place a meter ruler on the card, measure across as many waves as possible and divide that length by the number of waves (gives the wavelength)
- count the number of waves passing a point in 10 seconds and divide by 10 (gives the frequency)
- calculate wave speed using wave speed = frequency x wavelength
Describe how you would calculate the wave speed on an elastic cord
- set up a vibration generator, power supply, elastic cord, masses and a hanger, a wooden bridge and pulley on a clamp
- turn on the vibration generator
- use a meter ruler to measure as many half wavelengths as possible, then divide total length by the number of half waves then times by 2 (gives the wavelength)
- frequency is the frequency of the power supply
- use wave speed = frequency x wavelength
What is the law of reflection?
angle of incidence = angle of reflection
What 3 things could happen when a wave arrives at an interface (boundary between 2 mediums)?
- absorbed
- transmitted (continue travelling)
- reflected
Describe the angle of incidence
the angle between the incoming ray and the normal
Describe the angle of reflection
the angle between the reflected ray and the normal
Reflection produces a _____ image.
virtual
What is specular reflection?
- happens when a wave is reflected in a single direction by a smooth surface
What is diffuse reflection?
- happens when a wave is reflected by a rough surface and the reflected rays are scattered in lots of directions
What is refraction?
when light passes from one medium to another with a different optical density, the light changes direction
Describe how to investigate refraction
- place a transparent rectangular block on a piece of paper and trace around it
- use a ray box to shine a ray of light in the middle of one side of the block and trace the incident ray and emerging ray
- remove block and join up the lines to show the path of the refracted ray
- draw the normal where the light ray entered the block and use a protractor to measure the angle of incidence and the angle of refraction
- repeat experiment with different materials of block
Describe how to investigate reflection
- draw a straight line on a piece of paper and place an object so its side lines up
- shine a ray of light at the object and trace the incoming and reflected light beams
- draw the normal where the ray hits the object
- use a protractor to measure the angle of incidence and reflection, and make note of the width and brightness of the reflected ray
- repeat with different objects
Define electromagnetic waves
Transverse waves that transfer energy from the source of the waves to an absorber
All electromagnetic waves are …
- transverse
- can travel through a vacuum
- all travel at the same speed in a vacuum
Name the 7 types of electromagnetic waves, starting with the low energy
- radio waves
- microwaves
- infrared
- visible light
- ultraviolet
- x-rays
- gamma rays
Describe the red end of the EM spectrum
- lower energy
- long wavelength
- low frequency
Describe the violet end of the EM spectrum
- higher energy
- short wavelength
- high frequency
What are radio waves use and why?
- used for long-range communication
- because they can be reflected from the Earth’s atmosphere
What are microwaves use and why?
- satellite communications
- because microwaves can penetrate Earth’s atmosphere
What are infrared use and why?
- optical fibre communication
- because they can undergo total internal reflection
What is visible light use and why?
- taking photos and videos ( and seeing)
- cameras are set up to detect visible light
What is ultraviolet use and why?
- for detecting security ink ( and suntan)
- because it fluoresces with ultraviolet lighting
What is X-Rays use and why?
- to photograph bones
- because X-Rays can penetrate soft tissues but not bones
What is gamma rays use and why?
- to sterilise medical tools
- because gamma kills bacteria
What is the danger of microwaves?
high intensity microwaves can cause heating of internal organs
What is the danger of gamma, x-rays and high intensity UV?
- can harm cells and cause cancer
- because they are highly ionising
Describe the colour black as an absorber/emitter
good absorber
good emitter
Describe the colour dull/dark as an absorber/ emitter
reasonable absorber
reasonable absorber
Describe white as an absorber/emitter
poor absorber
poor emitter
Describe silver as an absorber/emitter
very poor absorber
very poor emitter
If a material is a poor absorber, it will be a good …
reflector
Describe the practical investigating infrared radiation using colour
- set up four identical flasks painted black, grey, white and silver
- fill the flasks with hot water, ensuring the measurements start from the same initial temperature
- note the starting temperature, then measure the temperatures at regular intervals
- plot the results on a graph
All warm objects emit thermal radiation in the form of ………..
infrared waves
Define a perfect black body
An object that absorbs all of the radiation that hits it and does not reflect/transmit any radiation
What are the 3 sets of words you use to describe an image?
- magnified (bigger) or diminished (smaller)
- inverted (upside down) or upright
- real (on the opposite side of the lens) or virtual (on the same side of the lens)
What do filters do?
Filters absorb every colour but one, which they transmit.
