Waves Flashcards
what do waves do?
transfer energy and information without transferring matter; the particles oscillate about a fixed point
what are features of transverse waves?
- have peaks and troughs
- vibrations are at right angles to the direction of travel
- an example = light
what are features of longitudinal waves?
- consists of compressions (particles pushed together) and refractions (particles moved apart)
- vibrations are in the same direction as the direction of travel
- an example = sound
amplitude definition
the distance from the equilibrium position to the maximum displacement
wavefront definition
a line joining points on a wave at the same point in their wave cycle at a give time
frequency definition
the number of waves that pass a single point per second
wavelength definition
the distance between a point on one wave and the same point on the next wave
time period definition
the time taken for one complete wave to pass a fixed point
what is the speed of a wave equal to?
the product of the frequency and wavelength
what is frequency of a wave equal to?
the reciprocal of the time period (1/time period)
what is frequency measured in?
hertz (Hz)
what is the doppler effect?
- if a wave source is moving relative to an observer, there will be a change in the observed frequency and wavelength due to the doppler effect
- this is because the wave fronts either get bunched together or spaced apart
- an example of this is when the siren of an ambulance is high-pitched as it approaches you, and low-pitched as it goes away
when can all waves be reflected?
when they travel from a medium of low optical density (such as air) to one of much higher optical density (such as glass)
what does the law of reflection state?
angle of incidence = angle of reflection
when a wave is reflected what happens to the frequency, wavelength and speed
they are all unchanged
when can all waves be refracted?
when the speed of a wave changes when it enters a new medium
what happens to the speed of a wave when it enters a denser medium?
its speed decreases and it bends towards the normal
what happens to the speed of a wave when it enters a less dense medium?
its speed increases and it bends away from the normal
what happens to the frequency, wavelength and velocity of a wave when it is refracted?
- the frequency stays the same
- the wavelength changes
- as a result, the velocity must change
what is the order of the electromagnetic spectrum?
radio -> microwave -> infrared -> visible -> ultraviolet -> x-ray -> gamma ray
as the EM spectrum goes from radio to gamma ray, what happens to the wavelength and frequency?
the wavelength decreases and the frequency increases
what speed do all the EM waves share?
all electromagnetic waves travel with the same high speed in a vacuum and the same speed in air
what are radio waves used for and why?
- radio and television communicators
- they have a long wavelength and are reflected by a layer of the atmosphere called the ionosphere
what are microwaves used for and why?
- satellite transmissions and in cooking
- they have a greater frequency (shorter wavelength) and they are more penetrating so can pass through the ionosphere and penetrate deep into food
what is infrared radiation used for?
heaters and night vision equipment
what is visible light used for?
fibre optics and photography
what is ultraviolet light used for?
fluorescent lamps
what are x-rays used for and why?
- medical imaging and in security
- they have a very short wavelength and high frequency and they can penetrate material easily
what is gamma radiation used for and why?
- sterilising food and medical equipment
- it has high energy
what are the hazards of microwaves?
they can cause internal heating of body tissues
what are the hazards of infrared radation?
they can cause skin burns
what are the hazards of ultraviolet light?
ultraviolet light exposure increases the risk of skin cancer and blindness
how can you prevent the hazards of UV light?
wear sun cream and sun glasses to prevent over-exposure in summer
what are the hazards of x-rays and gamma rays?
they are ionising radiation that can cause mutations leading to cancer
how can you prevent the hazards of x-rays and gamma rays?
- exposure to these kinds of radiation should be minimised
- you can do this by using protective shielding made of very dense materials such as lead
what are light waves?
transverse waves that can be reflected and refracted
how can reflection of light be shown?
when light reflects at a plane mirror and forms an image - this can be represented by a ray diagram
how can refraction of light be shown?
when light is passed through a glass slab at an angle to its normal
what happens to the angle of incidence when a light enters a more optically dense medium?
the angle of incidence is greater than the angle of refraction
what happens to the angle of incidence when a light enters a less optically dense medium?
the angle of incidence is smaller than the angle of refraction
what does snell’s law state?
it relates the angle of incidence and the angle of refraction to the refractive index of a medium
what is total internal reflection?
- at a certain angle of incidence called the critical angle, the light will travel along the boundary between the two media
- total internal reflection occurs when the angle of incidence is greater than the critical angle and the light reflects back into the medium
- for total internal reflection to occur, the light must be travelling from a more optically dense medium into a less optically dense medium (e.g. glass to air)
- the critical angle can be related to the refractive index by: n = 1/sin C
what is an optical fibre?
an optical fibre is a long thin rod of glass surrounded by cladding which uses total internal reflection to transfer information by light, even when bent
what are optical fibres used for?
they are used extensively in medicine (endoscopes, inside body flexible cameras) and communications (high speed data transfer)
what are sound waves?
longitudinal waves that can be reflected and refracted
what is the range of audible frequencies for a healthy human ear?
20Hz to 20,000Hz
how can you measure the speed of sound in air?
- you can make a noise at a known, large distance from a solid wall and record the time for the echo (reflected sound) to be heard
- then use speed = distance/time (where distance is 2x length)
what does an oscilloscope connected to a microphone show?
it can be used to display a sound wave and find its frequency and amplitude
the greater the amplitude of a sound wave…
the louder it is
the greater the frequency of a sound wave…
the higher its pitch
