Unit 4C - Lenses, Vision and Colours Flashcards
Lenses and Applications
- Lenses can make image size change related to object, change altitude or misshapen object
- Uses refraction twice when light ray enters and leaves lens to refocus light
Lens
- Thin, transparent glass/plastic with at least one curved side (concave/convex)
- Many sizes and shapes for many purposes
Converging v. Diverging Lens
- Converging lens makes parallel rays converge (opposite for diverging)
- Extent of conversion/diversion determined by material and shape of lens
Focal Points of Lenses
- Lenses have focal point on each side from having two sides
- F’ → Same side as origin of light ray (opposite for F)
Rules of Rays for Converging Lenses
- Ray entering lens parallel to principal axis will pass through focal point
- Ray travelling through centre of lens keeps travelling in same direction
- Ray entering lens from focal point will leave parallel to principal axis
Refraction on Centre of Lens
Rays of light through centre of lens refracted by same amount on both sides as lens is nearly flat on both sides
Object of Converging Lens Beyond 2F
Image: Smaller, Inverted, Between 2F’ and F’, Real
Object of Converging Lens At 2F
Image: Same size, Inverted, At 2F’, Real
Object of Converging Lens Between 2F and F
Image: Larger, Inverted, Beyond 2F’, Real
Object of Converging Lens At F
No clear image
Object of Converging Lens Inside F’
Larger, Upright, Same Side as Object, Virtual
d0
- Distance from object to optical centre (centre of lens)
- Always positive
di
- Distance from image to optical centre
- Positive for real; negative for virtual
h
- h0: Height of object
- hi: Height of image
- Positive when measured upward; negative when measured downward
f
- Focal length of lens
- Distance from optical centre to focus
- Positive for converging; negative for diverging
Thin Lens Equation
1/d0 + 1/di = 1/f
Rules of Rays for Diverging Lenses
- Ray entering lens parallel to principal axis will pass opposite to prime focal point
- Ray through centre of lens keeps travelling in same direction
- Ray aimed at principal focus before getting refracted will pass parallel to principal axis
Magnification Equation
- M = hi/h0 = -di/d0
- Positive for upright image; negative for inverted image
First Lens Used
- Reading stone was converging lens (on two sides)
- Formed images upright and larger than object
Object of Diverging Lens
Image: Smaller, upright, virtual, same side as object
Filter
Object that has colour but still allows light to pass through.
Wheel of Colours
- Red, Yellow, Green, Cyan, Blue, Magenta
- = 60(n - 1), where n is the colour
Retina
Layer near the end of eye
Iris
Thin, veiny layer right in front of the lens
Lens
Large, circular shape behind iris
Pupil
- Gap in front of eye
- Between the iris and the lens
Optical Nerve
Nerves at the end (close to circle) and exit of eye
Presbyopia
- Far-sightedness from loss of elasticity of eye lens with age
- Needs converging lenses
Hyperopia
- Far-sightedness from light focusing behind retina
- Inability of eye to focus light from nearby objects
- Needs lenses with positive meniscus
Meniscus
- Positive meniscus: Converging lens
- Negative meniscus: Diverging lens
Myopia
- Near-sightedness from light focusing in front of retina
- Inability of eye to focus light from distant objects
- Needs lenses with negative meniscus
Reflective Surfaces/Pigments
Reflects what is in common with the surface
Additive vs. Subtractive Colour Theory
Adding colours vs. Taking colours away
Primary Colours
- Red, Green and Blue
- White: All Colours
- Black: No Colour
- Can be added and removed with spotlights, filters and pigments
