chapter 14 Flashcards
what is reflection?
light consists of waves. when plane waves reflect from from a flat barrier the reflected waves are at the same angle to the barrier as the incident waves. when each point on the wavefront reaches the barrier, it creates a wavelet moving away from the barrier. this wavelet lines up with previously reflected wavelets to form a reflected wavefront moving away from the barrier. all wavefront move at same speed. reflected wavefront=angle to barrier as incident wavefront.
how are incident and reflected waves similar?
same frequency and same speed = same wavelength
what is the law of reflection?
light rays used to show direction that light waves are moving in:
line perpendicular to mirror iks the ‘normal’
the ‘angle of incident’ is the angle between the incident ray and the normal
the ‘angle of reflection’ is the angle between the reflected ray and the normal
what is the normal?
the line perpendicular to the mirror
what is the angle of incidence?
the angle between the incident ray and the normal
what is the angle of reflection?
the angle between the reflected ray and the normal
what do measurements show for any light ray reflected by a plane mirror?
the angle of incidence=the angle of reflection
what is a virtual image?
the image formed by a plane mirror is virtual, upright (the same way up as the object), and laterally inverted (back to front but not upside down). it is formed at a place where light rays appear to come from after they have reflected (or refracted), it can’t be projected onto a screen like movies
what is a real image?
an image that can be seen on a screen and is formed by focusing light rays onto the screen
what is specular reflection?
reflection from a smooth surface is specular because parallel light rays are reflected in a single direction
what is diffuse reflection?
reflection from a rough surface is diffuse reflection because the light is scattered in different directions
what is refraction?
at the opticians they may test different lenses infront of your eyes, each lens changes the direction of light passing through it, the change in direction is refraction
how are light waves refracted?
when they travel across a boundary between air and a transparent media, this is because the speed of light changes at this kind of boundary
when light waves enter and leave a glass block the change of direction of each ray relative to the normal at each boundary is what?
towards the normal when light travels from air into glass and away from the normal when light travels from glass to air
because light travels more slowly in glass than in air,glass is said to be ‘optically more dense’ than aur. in general:
when light enters a more dense medium it is refracted towards the normal and when light enters a less dense medium it is refracted away from the normal
when does partial reflection happen?
when waves cross a boundary between two materials it could happen aswell as reflection
how can you investigate refraction of light?
use a ray box and rectangular glass block to investigate the refraction of a light ray when it enters the glass, the ray changes direction at the boundary between air and glass (unless it is along the normal)
at the point where the light ray enters the glass, compare the angle of refraction, with the angle of incidence
ANGLE OF REFRACTION ALWAYS LESS THAN THE ANGLE OF INCIDENCE
what are the rules of refraction?
light ray:
changes direction towards the normal when it travels from air into glass. the angle of refraction smaller than angle of incidence
changes direction away from the normal when it travels from glass into air. angle of refraction greater than angle of incidence changes direction
what does each colour in the visible light spectrum have?
its own narrow band of wavelength and frequency, each band merges into the adjacent bands
why are different light sources different colours?
because they all emit their own range of wavelengths
what are properties of stars and filament lamps?
they have a continuous range of wavelengths across the visible spectrum, a filament lamp is an example of a white light source
what are properties of lasers and neon lamps?
emit narrow range of wavelengths across
how do colour filters work?
they absorb certain wavelengths and transmit other wavelengths
e.g. if white light directed at a red filter, the filter transmits only red light because it absorbs all the parts of the white light spectrum except for red
what are primary colours of light?
red green and blue
because they can be mixed to make any colours of light
