Waves Flashcards
what is the amplitude of a wave?
the maximum displacement of a point on the wave from its undisturbed position
what is the frequency of a wave?
the number of complete waves that pass a point per second
what is the period of a wave?
amount of time taken for a full cycle of the wave to pass a point
what is wave speed?
speed at which energy is being transferred by the wave
what 3 things can happen at a boundary between 2 different materials?
- absorbed, which transfers energy to the material’s energy stores
- transmitted - often causes refraction
- reflected
what is specular reflection?
when a wave is reflected in a single direction by a smooth surface
it forms a clear image
what is diffuse reflection & why does it occur?
when a wave is reflected by a rough surface & reflected waves are scattered in several directions
normal is different for each incident ray so angle of incidence is different for each ray so angle of reflection different
the surface appears matte
image is blury
how does density affect wave speed?
the greater the density, the lower the wave speed
what is optical density?
how quickly light can pass through an object
the higher the optical density, the slower light waves can travel through it
what do em waves transfer energy from & to?
from a source
to an absorber
how are radio waves produced & how do they transfer data?
- an alternating current has oscillating charges, which produce oscillating magnetic fields
- this produces electromagnetic waves/radio waves
- the frequency of waves = frequency of alternating current
- energy is transferred from waves to the electrons in the material of the receiver, causing the electrons to oscillate at the same frequency as the waves
- if circuit is complete, this generates alternating current in the receiver (same frequency as radio wave)
what are the uses of radio waves & why are they suitable?
long-distance communication
radio waves with longer wavelengths diffract/bend around the curved surface of Earth
radio waves with shorter wavelengths reflect off the ionosphere
what are the uses of microwaves & why are they suitable?
satellite communication
can easily pass through Earth’s watery atmosphere
cooking food
absorbed & transfer energy to water molecules in food
what are the uses of visible light waves & why are they suitable?
optical fibres
visible light is not easily absorbed or scattered by fibres
what is radiation does a measure of?
risk of harm from the body being exposed to radiation
not
total amount of radiation absorbed
what does the risk of radiation depend on?
total amount of radiation absorbed & type of radiation
what is the principal focus for a convex lens?
the point where rays of light parallel to the axis meet
what is the principal focus for a concave lens?
the point behind the lens where rays hitting lens parallel to axis seem to come from
what are the 3 rules for refraction in a convex lens?
- an incident ray parallel to axis refracts through lens & passes through principal focus on the other side
- an incident ray passing through the principal focus refracts through the lens & travels parallel to the axis
- an incident ray passing through the centre of the lens continues in same direction
what are the 3 rules of refraction in a concave lens?
- an incident ray parallel to the axis refracts through lens & travels in line with principal focus (appears to have come from the principal focus)
- incident ray passing through the lens towards principal focus refracts through lens & travels parallel to axis
- incident ray through the centre continues in same direction
how does the distance from the lens affect the image produced?
convex lenses:
an object at 2f produces a real, inverted image the same size as the object at 2f
an object between f & 2f produces a real, inverted image larger than the object beyond 2f
an object nearer than f produces a virtual, upright image larger than the object on the same side
what does the colour of an object depend on?
which wavelength of visible light is reflected most strongly
what do non-primary-coloured objects reflect?
the wavelengths of that colour
or
the wavelengths of the primary colours that mix together to make that colour
how do filters for non-primary colours work?
they transmit the wavelengths of light for that colour & the wavelengths of the primary colours that can be added together to make that colour