Topic 9 light

Question 1

Define light

Answer 1

• EM wave that is self-propagating combo = oscillating electric + magnetic fields

Question 2

What is the speed of light?

Answer 2

• Same no matter direction
• c = 2.99792458x10^8
• In a vacume c = fλ

Question 3

What wavelengths are visible light?

Answer 3

380nm - 750nm

Question 4

Define refraction

Answer 4

• Ray of light transmitted through boundary between 2 materials of unlike index of refraction = ray bends

Question 5

What is the absolute index of refraction

Answer 5

n = speed of light in vacum/speedof light in material

Question 6

What is the relative index between 2 materials?

Answer 6

Relative index = n1/n2
- If n2>n1 = ray bend towards normal
- If n1>n2 = ray bends away from normal
- If n1 = n2 = refraction doesn’t bend light beam

Question 7

What is Snells law?

Answer 7

𝒏𝒊 𝒔𝒊𝒏 𝜽𝒊 = 𝒏𝒓 𝒔𝒊𝒏 𝜽𝒓

Question 8

Define reflection

Answer 8

• Light hits a surface = bounces back
• How we see objects

Question 9

What is the law of reflection?

Answer 9

• Reflected light leaves surface at same angle as incident
• 𝜽𝒊 = 𝜽𝒓𝒇

Question 10

Describe the 2 types of reflection

Answer 10

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

Question 11

Define total internal reflection

Answer 11

• Complete reflection of incident ray at boundary = no transmission
• Only for waves where medium reflective index reduced

Question 12

Define critical angle

Answer 12

𝜽c = sin-1 n2/n1
- If incidence angle > critical = no transmission

Question 13

Describe converging lenses

Answer 13

• Positive lense
• Thicker at center
• Converge bean of parallel light > focus
• Real focus

Question 14

Describe diverging lens

Answer 14

• Negative
• Thinner in center
• Diverge beam of parallel light from focus
• Virtual focus

Question 15

Define focal length

Answer 15

Distance from focus > lens

Question 16

What is the lens equation?

Answer 16

• Rays passing through form image positive distance = d2
  1/d1 + 1/d2 = 1/f
• Real image at d2 if d1>f

Question 17

How are the d2 images formed for both lenses?

Answer 17

• Converging = inverted + magnified
• Magnification = di/do = d2/d1 = - y2/y1
• Diverting = erect + magnified

Question 18

What is the application of lenses in the eyes?

Answer 18

• Cornea + crystalline = positive = real image on retina
• Corrective lenses = either +/- depending on condition
• Presbyopia = positive
• Myopia = negative

Question 19

What is the power of the lens?

Answer 19

P = 1/f
- Unit = diopters = D

Question 20

What happens when 2 refracting interfaces in succession?

Answer 20

• Lensmaker’s equation:
  1/f = (n-1) ( 1/r1 - 1/r2)
• r = radii of curvature
• r = + if curvature = to right of surface

Question 21

Shapes of lenses

Answer 21

POSITIVE FOCAL
- Biconvex
- Planoconvex
- Positive meniscus
NEGATIVE FOCAL
- Biconcave
- Planoconcave
- Negative meniscus

Question 22

What type of lenses are isolated cornea + crystalline lenses?

Answer 22

• Isolated cornea = negative meniscus
• Crystalline =asymmetrical biconvex lenses