Objects may be luminous or non-luminous (ie. Emits its own light)
Some definitions:
Aperture: Hole or opening that controls the amount of light which is admitted
Beam: Wide stream of light rays traveling in the same direction
Concave: An inward curving surface
Cones: Cells located in the retina that respond to either red, green or blue light
Converge: Light rays moving towards each other
Convex: And outward curving surface
Dispersion: The separation of colours that make up white light
Diverge: Light rays moving so that they spread out
Focal Point: The point where light rays meet after passing through a lens
Opaque: Describes a substance that does not allow any light to pass through (brick wall)
Ray: Narrow beams that trace the path of light
Reflection: Where light bounces off a surface
Refraction: The changing in speed and thus direction of light as it passes into different media
Rods: Cells located in the retina that respond to the brightness of light, they are responsible for peripheral and night vision
Scattering: Where light is sent in many directions
Translucent: Describes a substance that allows some light to pass through meaning shapes can be seen but with little clarity (frosted glass)
Transparent: Describes a substance that allows most light to pass through meaning objects can be seen clearly (window)
Virtual focus: The common point from where light rays appear to originate, ie. a focus that does not exist but is imagined or assumed by continuing light paths
The Moon
-Phases of the moon change on a 29.5 day cycle
-Caused by relative position of sun, moon and earth
-Half the moon is ALWAYS lit by the sun
-Light always travels in straight lines, so the moon may block the sun (lunar eclipse)
-The sun, moon and earth are on different planes
Phases:
Light Refraction
-Observations: Images in the water at an angle appear magnified and bent
-Apparent position is above the actual position
-Refraction occurs when light travels between media
-Slows down, wavelength changes
-Light through air: 3x108 m/s (300 000 000)
-Light through water: 2x108 m/s (200 000 000)
-Light through glass: 2.25x108 m/s (225 000 000)
-Directional change as it enters the second medium
-When approaching at a perpendicular angle, refraction does not occur
-Refracted light reaches the eye as if it were approaching from a different angle
-After reaching the eye, light is traced back as a straight line
-Traced lines will have a focus different from where the actual ray originates
-Light bends towards the normal as it slows, and away as it quickens
-Angle varies as prism is turned, closer/further to normal means less/more refraction
Pinhole Camera
-The image shown will be upside down, as rays travel through the pinhole and to a point on the opposite face
-When the camera is moved toward the object, image will be larger and blurrier
-When the camera is moved away from the object, image will be smaller but sharper
-A bigger pinhole will produce brighter but blurrier images because more light is able to enter
-A smaller pinhole will produce sharper but duller images
Mirrors and lenses
Always measure the angle from the ray to the normal
The focal length is measured from the middle of the lens to the focal point
-The angle of incidence is equal to the angle of reflection on a plane mirror
-Biconvex Lens: converges light
-Thicker biconvex lens: focal length will be shorter because the curve is at a greater angle
-Biconcave Lens: diverges light (virtual focus)
-Concave mirror: reflects and converges light
-Convex mirror: reflects and diverges light (virtual focus)
A: Biconvex lens
B: Biconcave lens
C: Triangular Perspex
D: Rectangular Perspex
The Eye
The eye works a bit like the pinhole camera; the image will be upside down and instead of a pinhole there is the pupil
Cornea: Transparent front part of the eye connecting to the sclera through which light enters. Light is refracted here, but not as much as the lens
Sclera: The hard, flexible outer layer of the eye which is attached to tendons
Iris: The coloured part of the eye, it contracts and expands to control the amount of light entering the eye.
Muscle for movement: Controls eye movement
Vitreous Humour: Jelly-like substance that fills the space betwen the lens and the retina, helps to maintain eye shape
Lens: Biconvex structure that refracts light so that it focuses on the retina. Its shape can be changed by the ciliary muscle.
Aqueous Humour: Watery substance filling the space between the lens and the cornea
Suspensory ligament: Holds the lens in place, is directly attached to the lens
Ciliary muscles: Changes the shape of the lens in order to accommodate distances to an object. It contracts to round the lens for close work, and relaxes to flatten the lens for longer distances. It is connected to the suspensory ligament.
Retina: Sensory tissue lining the back of the eye containing photoreceptors (cone and rod cells) that capture light rays and convert them into electrical impulses. Looks like a thin, murky grey to pink film.
Choroid: The layer between the retina and the sclera that contains blood vessels and connective tissue
Blind Spot: This is the location where the retina joins to the optic nerve, meaning there are no photoreceptors in the area. When an image is at this certain position, it cannot be seen.
Optic Nerve: Transport messages from the photoreceptors to the brain
Pupil: Hole in the centre of the eye through which light passes, its size is controlled by the iris
Destinations for a light ray:
1. Outer Eye
2. Cornea
3. Aqueous Humour
4. Iris and pupil
5. Lens
6. Retina
7. Choroid via optic nerve
8. Sclera via optic nerve
9. Optic nerve
10. Brain
Seeing Colour
Cone cells are responsible for colour.
-Sensitive to red, green and blue
-These are the primary colours of light; they cannot be made by mixing other colours
-Note: They are not the same as paint
-Cone cells concentrated in the middle of the retina, with fewer on the periphery
-White light contains all colours
-When white light hits an object, all colours are absorbed except the colour that it appears to be which is reflected allowing us to see it
-We see a wide range of colours because different combinations and amounts mix to create various colours and shades.
Colours Combined Colour observed
Red + green + blue White
Red + green Yellow
Red + blue Magenta
Green + blue Cyan
Yellow + magenta + cyan White
*The secondary colours of light are magenta, cyan and yellow. They form when the primary colours overlap
