P6-waves Flashcards
what is the direction of the oscillations in transverse waves?
they are perpendicular to the direction of energy transfer
give three examples of transverse waves:
light waves, ripples in water, a wave on a string ( like on a guitar)
what direction are the oscillations of a longitudinal wave?
they are parallel to the direction of energy transfer
give two examples of longitudinal waves:
sound waves in air shock waves (e.g seismic waves)
how do waves transfer energy?
When waves travel through a medium,the particles of the medium oscillate, transferring energy between each other. (particles stay in the same place though)
what is the amplitude of a wave?
the max. displacement of a point on the wave from it’s undisturbed position.
what is the wavelength of a wave?
the distance between the same point on two adjacent waves.
what is the frequency of a wave?
the number of complete waves passing a certain point per second. measured in Hz
what is 1Hz equal to?
1 wave per second
what is the equation linking frequency, wave speed and wavelength?
wave speed (m/s)= frequency (Hz) x wavelength (m)
when are waves refracted?
when a wave crosses a boundary at an angle, it’s direction gets changed.
what determines how much a wave is refracted?
How much the wave speeds up/slows down . This depends on the density of the material
what happens to a wave that slows down when it crosses the boundary?
It bends towards the normal.
what happens to a wave that speeds up as it crosses a boundary?
it bends away from the normal
what changes and what stays the same when a wave is refracted?
the wavelength changes, the frequency stays the same.
what is the optical density of a material?
a measure of how quickly light can travel through it. Higher optical density-light waves travel slower.
Drawing a ray diagram for refraction:
draw in the __________between 2 materials, and the _______
draw an _____ ray which meets the normal at the boundary. the < between the ray and the normal is the angle of _________.
now draw the ________ray . the angle of refraction depends on the _______ of the material.
boundary, normal. Incident, incidence.refracted, optically dense.
radio waves are apart of…?
the electromagnetic spectrum. EM waves are made up of oscillating electric and magnetic fields.
radio waves travel at the speed of what?
light
are radio waves transverse or longitudinal?
transverse.
can radio waves travel through a vacuum?
yes
give three examples of signals that radio waves carry:
Tv, radio and mobile phone signals
give another use of radio waves:
they can wirelessly connect a computer to a printer. Bluetooth
State three properties of short length radio waves:
they carry more information
they have a shorter range
they spread out less ( they don’t weaken as much)
what are radio wave lengths of less than 1 metre used for and why?
they are used for TV broadcasting from TV masts. This is because they carry a lot of information.
what are radio waves of length 1m-100m used for and why?
local radio stations, emergency services. they have a short range.
what are radio waves length greater than 100 m used for?
national/international radio stations. They have a longer range.
what is different about how long length radio waves compared to short ones?
Long waves diffract around the curved surface of the earth.They can diffract around hills and into tunnels. Whereas short wavelengths are reflected from the ionosphere
transmitting and receiving radio waves:
1-microphone produces an_______ ______
2-this causes_____to oscillate in _______ aerial
3-the aerial emits ______ waves
4-the waves are absorbed by ______ aerial
5- electrons_____ in the receiver, generating an _______ current with the same _______ as radio waves.
alternating current electrons, transmitter radio receiver oscillate, alternating frequency
if you can’t hear radio waves, how can radios produce the noise from the waves?
radio waves carry signals which the receiver converts into sound waves.
How do lenses work?
they refract light and change it’s direction.
what are the two types of lens?
concave and convex.
what is the shape of a convex lens and how does it refract light?
It bulges outwards () . Rays of light parallel to the axis are brought together and converge at the principal focus.
what is the shape of a concave lens and how does it refract light?
it caves inwards )(. rays of light parallel to the axis diverge.
what is the axis of a lens?
a line passing through the middle of the lens
what is the principal focus of a convex lens?
where the rays hitting the lens parallel to the axis all meet.
what is the principal focus of a concave lens?
where all the rays hitting the lens parallel to the axis APPEAR to all come from (they can be traced back until they all appear to meet up at a point behind the lens)
what is the focal length?
the distance from the centre of the lens to the principal focus (there’s a principal focus on either side of the lens)
what are the three rules of convex lenses?
1-an incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
2-an Incident ray passing through the principal focus will refract through the lens and travel parallel to the axis
3-an incident ray traveling through the centre of of the lens carried on in the same direction.
what are the three rules for concave lenses?
1-An incident ray parallel to the axis will refract through lens and travel in line with the principal focus
2-an incident ray travelling through lens towards principal focus will refract and travel parallel to the axis
3-incident ray passing through centre carries on in same direction
what is a real image and give an example:
the light from an object comes together to form an ‘image on a screen’. Eg the image formed on an eye’s retina.
what is a virtual image? give an example
where rays are diverging so light appears to be coming from somewhere else. Eg a mirror. you can use a magnifying glass to get a virtual image.
what three things are needed to describe an image?
1-size compared to object
2-if it’s upright or inverted compared to object
3-of its real or virtual
will a concave lens always give a real or virtual image?
virtual
