LIGHT Flashcards
what things affect what waves do at a boundary
- the material
- the wavelength of the wave
angle of reflection =
angle of incidence
what is refraction
when a wave changes speed or direction when changing from one medium to another
what happens when a ray of light is reflected onto a rough surface
- each rays of light are reflected in different directions
- angle of incidence is different for each ray
what happens when light passes from air into glass
the speed of light decreases, causing the direction of the waves to change
what happens when waves slow down in a ray diagram
they bend towards the normal
what happens when waves speed up in a ray diagram
they bend away from the normal
when do waves not change direction
when they enter or leave the medium at right angles to the surface
what is the wavefront
an imaginary line that connects all the same points in a set of waves
what do all lenses do
they refract light
why does the central ray in a convex lens not get refracted
because the ray is passing directly along the normal
what is the centre of the lens called
the principal axis
what is the point that all other refracted rays are focused on called
principal focus
what is the focal length
the distance from the centre of the lens to the principal focus
properties of images formed from convex lenses
- inverted
- real
meaning of real image
an image where rays of light actually meet at a point
what properties would an image have if the object is more than 2 focal lengths from the lens
- diminished
- inverted
- real
what happens if the object is between 1 and 2 focal lengths from the lens
- magnified
- inverted
- real
how do we show the image in a magnifying glass ray diagram
we draw dotted lines to extend the rays behind the lens, where the dotted lines meet is the position of the image
why dow e use dotted lines for magnified ray diagrams
because these do not represent the actual path of the rays
properties of an image formed by a magnifying glass
- magnified
- same way up as the object (upright)
- virtual
how can we tell if a ray diagram is one from a magnifying glass
the object is less than one focal length away from the lens
meaning of virtual
when the rays do not actually meet at a point, they only appear to meet, so we couldnt see this image on a screen
when is the only time a convex lens produces a virtual image
when its used as a magnifying glass
properties of convex lens
thicker in the centre than the edges
properties of concave lenses
they are thicker at the edges than in the centre
what do concave lenses make light do
spread out(DIVERGE)
where is the principal focus in a concave lens
behind the lens
why do we draw a dotted line to show the refracted ray in a concave lens
because a concave lens is not actually focusing the light at the principal focus, it only appears to be
how can we show the position of an image in a concave lens ray diagram
where the dotted line and the first ray meet
properties of concave images
- diminished
- right way up
- VIRTUAL
why are concave images virtual
because the rays do not actually cross there, they only appear to cross there
what is specular reflection
when all light rays are reflecting in a single direction (smooth surface)
what is diffuse reflection
where light rays are scattered and each rays angle of incidence is different
what happens when we shine light through a prism
it splits into a spectrum
what colours are in the spectrum of light
red, orange, yellow, green, blue, indigo, violet
what does the colour of an object depend on
which wavelengths of light are absorbed, transmitted or reflected
why do white objects appear white
because they reflect all wavelengths of visible light equally
why do black objects appear black
because they absorb all the wavelengths of visible light
meaning of opaque
objects that do not transmit light, only absorb or reflect it
how do coloured filters work
by absorbing specific wavelengths and transmitting (allowing through) other wavelengths
what happens when you shine white light on a red filter
the filter absorbs all colours of visible light except red, so only red light is transmitted through the filter
what type of objects can transmit light
transparent and translucent objects
why cant we see through translucent objects
because they scatter the light rays so we cannot see through them clearly
why do white objects appear white
because they reflect all wavelengths of visible light equally
why do black objects appear black
because they absorb all the wavelengths of visible light
what happens when white light is shone onto a red object
the red absorbs all the colours of white light, apart from red which is reflected
what happens when you shine a red filter onto a red object
the red filter absorbs all colours of light except red, which is transmitted,
the red light can then reflect off the red object, so the object appears red
what happens if you shine a red filter on a green object
the red filter absorbs all wavelengths of visible light apart from red, which is transmitted
the green object completely absorbs the red light so none is reflected
the green object will appear black, as it is not reflecting any light
what factors affect what a wave does at a boundary
- the material
- the waves wavelength
why cant we see through translucent objects clearly
because they scatter light rays
what does the wavelength and intensity of radiation depend on
the temperature of the object, very hot objects emit shorter wavelength radiation than cooler objects
what dies a perfect black body do
absorbs all the radiation incident on it, no radiation is transmitted or reflected
- best possible emitter of radiation
what will happen if an object is warmer than its surroubdibgs
it will emit more radiation than it absorbs, and its temperature will decrease
what will happen if an object is cooler than its surroundings
it will absorb more radiation than it emits, and its temperature will increase
what will happen to radiation if an object is at constant temperature
it will absorb and emit radiation at the same rate
how does radiation affect the temperature of the earth
- the sun emits short wavelength radiation, such as visible light and UV
- this radiation travels to the earth
- some of the radiation is reflected eg by clouds
- the remaining radiation can then be absorbed by the earth
- this causes the temperature of the earth to increase
- the earth then emits infrared radiation back into space
- however some of the energy of the infrared is trapped by greenhouse gases
what happens to radiation as the levels of greenhouse gases increase
more heat energy is trapped in the atmosphere and less is radiated back into soace
what factors can affect how much energy is radiated from the earth
cloud cover - cloudier nights tend to be warmer than clear nights, because clouds can reflect infrared back to earth and prevent it being radiated into space
features of matt black surfaces
best emitters and absorbers of infrared radiation
what do the wavelength and the intensity of radiation depend on
the temperature of the object
how does temperature change with wavelength size
- very hot objects emit shorter wavelength radiation than cooler objects
- as the object gets hotter, it emits more short wavelength radiation
