Mcat Physics Lecture 8

Front 1

Electromagnetic wave

Back 1

traveling oscillation of an electric and a magnetic field

fields are perpendicular to each other and directions of propagation is perpendicular to both fields

it is a transverse wave

generated by acceleration of electric charge

Front 2

Speed of electromagnetic wave (c)

Back 2

constant speed and always equal to ratio of magnitudes of electric field and magnetic field

c = E/B

energies of 2 fields are equal

Front 3

Poynting vector (S)

Back 3

describeds the rate and direction in which an electromagnetic wave is transporting energy per unit area

always perpendicular to both E and B

has a magnitude of EBsin0

Front 4

Light

Back 4

tiny sliver from the electromagnetic spectrum

Front 5

visible light

Back 5

includes wavelengths from 390 to 700 nm

shorter wavelengths correspond to violet light and longer wavelengths to red light

Front 6

ultraviolet light

Back 6

just beyond visible spectrum on smaller wavelength side

Front 7

infrared

Back 7

just beyond visible spectrum on longer wavelength side

Front 8

colors of visible spectrum

Back 8

Roy G. Biv

Red, orange, yellow, green, blue, indigo, violet

wavelengths toward violet have more energy

Front 9

index of refraction (n)

Back 9

constant for the medium light propagates through

n = c/v
n: index of refraction
c: speed of light in vacuum
v: speed of light in medium

since nothing exceeds the speed of light in a vacuum, all media have an index of refraction greater than 1

the greater the index of refraction, the slower light moves through that medium

n for water = 1.3
n for glass = 1.5

Front 10

plane-polarized light

Back 10

light with electric fields in one particular direction as a result of screening out photons not have an electric field in one particular direction (filter)

Front 11

isotropic light

Back 11

unpolarized light, white light

electric fields point in all directions

when polarized, it loses 1/2 of its intensity

Front 12

dual nature

Back 12

acts both as a wave and a particle

propagation properties can be described with wave theory

energy transformation properties are best described by particle theory

Front 13

angle of incidence

Back 13

angle at which light ray strikes the interface as measured from a line normal to the interface

equals angle of reflection

Front 14

angle of reflection

Back 14

angle at which light ray reflects off of interface as measured from a line normal to the interface

equals angle of incidence

Front 15

angle of refraction

Back 15

angle at which light ray refracts through the interface as measured from a line normal to the interface

given by Snell's law: n1sin01 = n2sin02

Front 16

Snell's law

Back 16

gives you angle of refraction

n1sin01 = n2sin02

Front 17

Energy of a single photon

Back 17

E = hf
E: energy of single photon
h: planck's constant
f: frequency

when light crosses into a new medium, frequency remains the same and wavelength changes

Front 18

total internal reflection

Back 18

occurs when light coming from a medium with higher index of refraction, causes angle of incidence to be so large that entire amount of photons will be reflected at the angle of reflection and none will refract

this angle of reflection is the critical angle

Front 19

critical angle

Back 19

angle at which light reflects when there is total internal reflection (no refraction)

0critical = sin^-1(n2/n1)
0critical: critical angle
n: index of refraction

Front 20

refraction of different waves at interface

Back 20

longer wavelengths (lower frequencies) move faster through a medium and therefore bend less at interface

shorter wavelengths (higher frequencies) move slower through medium and therefore bend more at interface

Front 21

diffraction

Back 21

another type of wave-bending phenomenon

when wave moves through a small opening, it bends around the corners of that opening

the smaller the opening and the larger the wavelength, the greater the diffraction

smaller the hole the greater the spreading of light

results in an image of light and dark bands or in dispersion and the creation of colors (depend upon destructive and constructive interference)

Front 22

virtual image

Back 22

does not actually exist outside the mind of the observer

no light rays emanate from virtual image

if a sheet of white paper is placed at the position of a virtual image, no image will appear on the paper

ex: reflection in a flat mirror, a mirage, image under water

Front 23

real image

Back 23

exists separately from the observer

rays of light actually intersect and then emanate from the point of intersection to form a real image

if a sheet of white paper is placed at the position of a real image, the image will appear on the paper

Front 24

two types of mirrors

Back 24

1. convex
2. concave

Front 25

two types of lenses

Back 25

1. diverging (concave), acts like convex mirror
2. converging (convex), acts like concave mirror (3Cs: a thiCk Center Converges light)

Front 26

radius of curvature

Back 26

for small section of curve is radius of extended circle

smaller radius of curvature indicates a sharper curve

Front 27

focal point

Back 27

where light from horizontal rays is reflected by concave mirrors (or refracted by converging lenses) to focus on a single point

varies with frequencies

Front 28

focal length

Back 28

length of separation between mirror or lens and the focal point

it is related to radius of curvature

fmirror = 1/2r
fmirror: focal length
r: radius of curvature

focal point for a lens (flens) is affected by the refractive indices of the lens and the medium that the lens is in

flens is also affected by radii of curvature of both sides of the lens

Front 29

lens maker's equation

Back 29

1/flens = [(n1/n2)-1][(1/r1)-(1/r2)]

when n1=n2, lens will not refract light

Front 30

power

Back 30

measured in diopters, which has equivalent units of m^-1

the inverse of the focal length

P = 1/f
P: power
f: focal length of lens

Front 31

lateral magnification (m)

Back 31

ratio of size of image to size of object (compare heights)

equal to negative of ratio of distance of image and distance of object from mirror or lens

negative sign indicates that if both distances are positive, than the image is inverted

m = -(di/do) = (hi/ho)
m: magnification
di: distance of image
do: distance of object
hi: height of image
ho: height of object

Front 32

thin lens equation

Back 32

for any mirror or lens, distance of image is related to focal length and distance of object

(1/f) = (1/do) + (1/di)
f: focal length
do: distance of object
di: distance of image

applies to mirrors as well

all measurements are given positive or negative values based upon their position relative to the mirror or lens

Front 33

1st rule of mirrors and lenses

Back 33

draw an eye where observer will stand, and label side: positive, real and inverted (PRI)

"I (eye) am positive that real is inverted"

images on side opposite the eye, are: negative, virtual and upright (NVU)

Front 34

2nd rule of mirrors and lenses

Back 34

front of mirror is side that I (eye) am on

back of lens is side that I (eye) am on (stand behind camera to view object)

objects are always positive when they are in front of a lens or mirror and always negative when they are behind a lens or mirror

Front 35

3rd rule of mirrors and lenses

Back 35

if object is in front:
convex mirrors and diverging lenses make negative, virtual and upright images (NVU)

concave mirrors and converging lenses make positive, real and inverted images (PRI), except when object is within the focal distance, in which case, they make a negative, virtual and upright image (NVU)

Front 36

concave mirror and converging lens

Back 36

f is always positive

Front 37

convex mirror and divergent lens

Back 37

f is always negative

Front 38

lateral magnification of a 2 lens system

Back 38

product of lateral magnification of each lens

M = m1m2

Front 39

Effective power of 2 lenses in contact with each other

Back 39

equal to sum of their individual powers

Peff = P1 + P2

Front 40

Electromagnetic radiation equations

Back 40

c = f (wavelength)
c: speed of light
f: frequency

n = c/v
n: refractive index
c: speed of light in vacuum
v: speed of light in medium

E = hf
E: energy of one photon
h: planck's constant
f: frequency

n1sin01 = n2sin02
n: refractive index

Front 41

Mirrors and lenses equations

Back 41

fmirror = (1/2)r
fmirror: focal length of mirror
r: radius of curvature

P = 1/f
P: power
f: focal length

(1/f) = (1/di) + (1/do)
f: focal length
di: distance of image
do: distance of object

m = -(di/do) = hi/ho
m: magnification
di: distance of image
do: distance of object
hi: height of image
ho: height of object