waves (reflection, refraction, lenses) Flashcards
what is the relationship between the angle of incidence and the angle of reflection when waves are reflected
when waves are reflected the angle of incidence is equal to the angle of reflection
what is the normal
the normal is a construction line perpendicular to the reflecting surface at the point of incidence
describe the image in the plane mirror
-virtual (it cannot be touched or projected onto a screen) -upright (if you stand in front of a mirror, you look the right way up) -laterally inverted (if you stand in front of a mirror, your left side seems to be on the right in the reflection)
Refraction
The change of direction of light waves when they pass from one medium to another at an interface
which way does light refract when it enters a more dense medium
it refracts towards the normal
which way does light refract when it enters a less dense medium
it refracts away from the normal
what happens when waves travel along the normal
they are not refracted
why are waves refracted
due to change of speed
what can refraction by a prism lead to
dispersion (the separation of visible light into its different colours)
what is the refractive index of a medium defined as
speed of light in vacuum (air) —————————————– speed of light in the medium
what us the relationship between refractive index, angle of incidence and angle of refraction
sin (angle of incidence) refractive index = ———————————- sin (angle of refraction) sin i n = ——– sin r
What is the relationship between refractive index and critical angle
1 refractive index = ———————– sin (critical angle) 1 n = ——— sin c
what is the critical angle
the critical angle, c, is the angle of incidence at which maximum refraction occurs (when the angle of refraction = 90°)
what is total internal reflection
total internal reflection is a special case of refraction, which occurs if the angle of incidence within the more dense medium is greater than the critical angle
how can visible light go through optical fibres
visible light can be transmitted through optical fibres by total internal reflection
what is an example use of light being transmitted through optical fibres by total internal reflection
the endoscope for internal imaging
how does a lens form an image
a lens forms an image by refracting light. each section of a lens acts like a tiny prism, each section refracting light as it goes in and again as it comes out
what happens with a convex lens
in a convex lens, parallel rays of light are refracted so that they come together (brought to a focus) at the principal focus (F)
what is another name for a convex lens
a converging lens
what can a converging lens be used as
a magnifying glass
what is the nature of images produced by converging lens
converging lenses focus the rays of light to form a real image
what is a real image
A real image is the image formed where the light rays are focussed.
what is a virtual image
A virtual image is one from which the light rays appear to come but don’t actually come from that image like in a mirror.
what is the focal length
the distance from the lens to the principal focus
what is the focal length of a lens determined by
-the refractive index of the material from which the lens is made -the curvature of the two surfaces of the lens
For a given focal length, the greater the refractive index, the …….. the lens
for a given focal length, the greater the refractive index, the flatter the lens. this means that lens can be manufactured thinner
what happens in a concave lens
in a concave lens, parallel ray of light diverge as if coming from the principal focus
what is another name for a concave lens
a diverging lens
what does a diverging lens do
diverging lenses refract the parallel rays of light so that they spread apart from one another. This means that they form a virtual image
what is the nature of an object defined by
P -position O -orientation (upright or inverted - relative to the object) T -type (real or virtual) S -size (diminished or enlarged - relative to the object)
equation for calculating the magnification produced by a lens
image height magnification = —————————- object height
what is the relationship between the power of a lens and the focal length
1 Power = ————- focal length 1 P = —– f
