Lecture 6: Light And Optics

Question 1

Speed of waves

Answer 1

1. Speed of any wave: v=f λ
   1a. V=m/s (in a vaccum v=c=3x10^8m/s=speed of light)
   1b. Frequency =f
   1c. λ=wavelength (m)

Question 2

Index of refraction

Answer 2

1. Index of refraction: n=c/v
   1a. Vaccum/Air: n=1
   1b. Any other media: n>1…so light moves slower here

Question 3

Electromagnetic spectra

Answer 3

1. Gamma->x ray->ultraviolet->Visible (VIBYOR) light->infrared->microwaves->radiowaves->long waves
   1a. Smallest/lowest λ /highest f —->biggest/highest λ/lowest f
2. Visible light: 400nm(purple)—->700nm (red)

Question 4

Energy of a photon

Answer 4

1. E=hf
   1a. Highest frequency, lowest λ, smallest=highest energy (purple)

Question 5

White vs black light

Answer 5

1. White: mixture of all visible colours
2. Black: how our brain interprets no light striking our retina

Question 6

Polarization overview

Answer 6

1. Changing light to have 1 electric field
2. To make polarized light, we shine light at a Polaroid with horizontal hydrocarbon chains ….blocks light from going through (only vertical components get through)
3. Loses intensity by 1/2

Question 7

Linear polarization

Answer 7

1. Shine unpolarized light through vertical transmission axis…E1 is 1/2 intensity of E0
2. To find intensity of E2 use Malus’ law: I=(Io)cos^20
   2a. I=intensity of E2
   2b. Io=original intensity
   2c. Cos^20: angle between 2 transmission axis
3. Remove filter=less intense

Question 8

Circular polarization

Answer 8

1. Shift linear polarized light and phase shift it 90 degrees to make it out of phase
2. Use right hand rule

Question 9

Diffraction

Answer 9

1. Occurs when a wave encounters an obstacle/gap smaller than its wavelength so the wave spreads out/diffracts as it passes obstacle
   1a. Smaller gap=wider diffraction

Question 10

Young’s double slit experiment

Answer 10

1. Combines diffraction and interference to prove light behaves like a wave
   1a. In phase waves: interfere constructively to create a maxima bright fringes (dsin0=m λ)
   1b. Out of phase waves: interfere destructively to create maxima dark fringes (dsin0=(m+1/2) λ

Question 11

Reflection

Answer 11

1. Angle of incidence=angle of reflection

Question 12

Refraction

Answer 12

1. Happens when light moves through a medium with a different refractive index
2. Shown through snells law: n1sin1=n2sin2
   2a. Light is slower when higher refraction index

Question 13

Total internal reflection (TIR)

Answer 13

1. When the critical angle where refraction ray bends so much it can’t get out into new material

Question 14

Thin film interference

Answer 14

1. Cancels out reflection

Question 15

Dispersion

Answer 15

1. When smth is split or spreads out
   1a. Chromatic dispersion: when a light spreads out because of its frequency
2. Higher frequencies have higher refractive indices: purple light travels slower than red light

Question 16

Mirrors vs lenses

Answer 16

1. Mirrors: reflect light
   1a. Concave
   1b. Convex
2. Lenses: refract light
   2a. Converge concave: makes parallels rays converge to a focal point
   2b. Diverge convex: makes parallel rays diverge, spreading out as if they came from a focal point

Question 17

Definition of images

Answer 17

1. Real or virtual
   1a. Real: light is from image point
   1b. Virtual: light only looks it was from image point
2. Upright/downright
   2a. Upright: image is oriented same as object
   2b. Inverted: image is flipped from up to down and left to right
3. Magnified or diminished
   3a. Magnified: image is larger than object
   3b. Diminished: image is smaller than object

Question 18

Focal length for spherical optics

Answer 18

1. Focal length=hald radius of curvature
   1a. F=r/2=c/2

Question 19

Shortcuts for images

Answer 19

1. Real images: always inverted, front of mirror/behind lens
2. Virtual images: always upright, behind mirror/in front lens, always for convex mirror , always for diverging lens (diminished as well)

Question 20

To draw images

Answer 20

1. Draw 3 lines all from top of object arrow: parallel, hitting centre of mirror, going through focal point

Question 21

Equation for object and image distances with mirrors and lenses

Answer 21

1. 1/f=1/o+1/i
   1a. F=focal point : (positive for concave mirrors/converging lenses) (negative for convex mirrors/diverging lenses)
   1b. O=object: positive in front of object (always in front for Mcat)
   1c. I=image: (positive for real) (negative for virtual)

Question 22

Magnification

Answer 22

1. M=hi/hi=-i/o

Question 23

Multiple lens system: microscope

Answer 23

1. MTotal=M1 x M2
   1a. Magnification of 2 lens system

Question 24

Lens power

Answer 24

1. P=1/f
   1a. If multiple lenses: Ptot=P1+P2… and ft=1/Pt

Question 25

Human eye

Answer 25

1. Near sighted (myopic): need diverging lenses because can’t see far
2. Far sighted (hyperopic): can’t see close so need converging lenses