Topic 9 light Flashcards
Define light
- EM wave that is self-propagating combo = oscillating electric + magnetic fields
What is the speed of light?
- Same no matter direction
- c = 2.99792458x10^8
- In a vacume c = fΞ»
What wavelengths are visible light?
380nm - 750nm
Define refraction
- Ray of light transmitted through boundary between 2 materials of unlike index of refraction = ray bends
What is the absolute index of refraction
n = speed of light in vacum/speedof light in material
What is the relative index between 2 materials?
Relative index = n1/n2
- If n2>n1 = ray bend towards normal
- If n1>n2 = ray bends away from normal
- If n1 = n2 = refraction doesnβt bend light beam
What is Snells law?
ππ πππ π½π = ππ πππ π½π
Define reflection
- Light hits a surface = bounces back
- How we see objects
What is the law of reflection?
- Reflected light leaves surface at same angle as incident
- π½π = π½ππ
Describe the 2 types of reflection
1) Specular = light hits flat surface = all light from single direction = reflected in single direction
2) Diffuse = light hits rough surface = reflected in wide range of directions
Define total internal reflection
- Complete reflection of incident ray at boundary = no transmission
- Only for waves where medium reflective index reduced
Define critical angle
π½c = sin-1 n2/n1
- If incidence angle > critical = no transmission
Describe converging lenses
- Positive lense
- Thicker at center
- Converge bean of parallel light > focus
- Real focus
Describe diverging lens
- Negative
- Thinner in center
- Diverge beam of parallel light from focus
- Virtual focus
Define focal length
Distance from focus > lens
What is the lens equation?
- Rays passing through form image positive distance = d2
1/d1 + 1/d2 = 1/f - Real image at d2 if d1>f
How are the d2 images formed for both lenses?
- Converging = inverted + magnified
- Magnification = di/do = d2/d1 = - y2/y1
- Diverting = erect + magnified
What is the application of lenses in the eyes?
- Cornea + crystalline = positive = real image on retina
- Corrective lenses = either +/- depending on condition
- Presbyopia = positive
- Myopia = negative
What is the power of the lens?
P = 1/f
- Unit = diopters = D
What happens when 2 refracting interfaces in succession?
- Lensmakerβs equation:
1/f = (n-1) ( 1/r1 - 1/r2) - r = radii of curvature
- r = + if curvature = to right of surface
Shapes of lenses
POSITIVE FOCAL
- Biconvex
- Planoconvex
- Positive meniscus
NEGATIVE FOCAL
- Biconcave
- Planoconcave
- Negative meniscus
What type of lenses are isolated cornea + crystalline lenses?
- Isolated cornea = negative meniscus
- Crystalline =asymmetrical biconvex lenses
