Light and Optics

Light Waves vs Sound waves

Sound waves:

-Longitudinal

-Needs a medium

-Since space is a vacuum cannot propagate in space (why we don’t hear the sun nuclear fission)

Light waves:

-Transverse

-Does NOT need a medium

Intensity is what

Energy of the wave (bright or dim)

I=A²

I=Power/4pir²

I=1/r²

E=hf

Energy of a PARTICLE

Photons

Color

For light

Amplitude=electric field strength

Frequency, wavelength, energy comparison line

Gamma rays-x rays-UV-ROYGBV-infared-microwaves-radiowaves

Radiowaves=Longest wavelength

Red-longest wavelength, smallest energy

Gamma-highest frequency, shortest wavelengths, most energy

Reflection

For reflection angle of incidence =angle of reflection

Refraction

theta2<theta 1 wave bent towards normal=SLOWING down

theta2>theta 1 wave bent away from normal so SPEEDing up

Index of refraction

n=c/vmedium

nvacuum=nair=1

n>_1 all slower than air

Refraction, indexes of refraction

n1sin(theta)=n2sin(theta)

n1>n2

Sintheta2>sintheta1

theta 2>theta 1

Speeding up

Critical angle

Sintheta=n2/n1

Theta at which theta 2=90 degrees

If theta>critical angle, refraction cannot happen so total internal reflection

Rules to know speed of light in water and speed of sound in water

Light slows down entering water, bends towards normal

Sounds speeds up entering water, away from normal (has to do with the compression ability)

Diffraction

Diffraction is the bending, spreading, and scattering of waves as they encounter an obstacle, pass through a gap, or navigate an aperture. This phenomenon occurs with all types of waves—including light, sound, and water waves—and is most prominent when the size of the obstacle or opening closely matches the wave's wavelength.

Light and sound

Dispersion

Light dispersion is the process where white light is separated into its component colors (the visible spectrum) because different wavelengths of light travel at different speeds and bend at different angles when passing through a medium. [1, 2]

Light only

Polarization

Only light transverse waves

Sounds cannot

Polarization of light is a fundamental property of light waves describing the specific orientation of their oscillating electric and magnetic fields. It determines the plane in which the light wave vibrates as it travels through space

Light vs sounds properties

Light and sound both:

-Both use wave speed V=lambda (f)

-Both reflect, refract, and diffract

Different:

-Different types of waves

Light: transverse sound: longitudinal pressure

-Light does not need medium whereas sounds does

-Light can polarize, sound cannot

-Light slows down when going from air to water

-Sound speeds up from air to water

Mirrors and Lenses

1/f=1/object distance + 1/image distance

m=-image/object

Focal length

+ for a converging lens or mirror

- for a diverging lens or mirror

Converging lens=convex

Converging mirror=concave

Object distance

+ always

Image distance

+ for real images

Magnification

+ for upright image

Concave vs convex mirror

Concave: converging mirror +f

Near focal point

-Image on same side as object

-Image inverted

-Real image (+image distance)

Convex: diverging mirror -f

Far focal point

-Image on opposite side

-Image upright

-Virtual image (-image distance)

Concave vs convex lenses

Concave: Diverging -f

Far focal point

-Image on same side

-Smaller and upright

-Virtual -image

Convex: converging +f

Close focal point

-Image on opposite side

-Real image +image

-Inverted and smaller

Converging for both lens and mirrors

Mirrors: Concave + real image, same side

Lens: convex + real image, opposite side

Myopia

Nearsightedness

Trouble seeing far away

Focal length too short

Diverging lens, concave lens

Lens power

P=1/f

f in meters!!!

Correcting myopia

1/object distance 1/infinity 0

Image of far object bring it closer in front of glasses

Flat mirrors in bathrooms for example

About same size

m=1

Object=-(image distance)

focal length is going towards infinity

Photoelectric effect

The photoelectric effect is the emission of electrons from a material when it is struck by electromagnetic radiation, such as light

Shining light on a metal, can eject electrons from metal (photo electrons)

Detect current-put into a circuit

Measure photoelectrons

Brighter light, brighter intensity (bright vs dim, # of photons), more current read, only if wavelength is short enough

Light behaves as a wave and as a particle

E=hf for particles (photons)

Light: Wave (intensity) and particles (photons)

DeltaKE=-deltaPE

Kemax=hf-(work function, bidnign energy)

KE max=-eVstop

Vary light frequency and battery voltage, measure current

Making a light source brighter (increasing intensity) only increases the number of ejected electrons, never their energy. Only changing the frequency can increase the electrons' energy

Context and importance in medical imaging devices

Photon is absorbed via photoelectric effect, is more prominent in denser tissues

Lungs-least dense (air)-precludes ultrasounds need to use XRAY

Heisenberg uncertainty principle deltaXdeltaP=constant

PET scan real specific, laser if we want delta X to lower for specific region, limits resolution in technologies

Mass to energy equation (:

E=mc²

c=3×10^8 m/s speed of light in a vacuum