electromagnetic waves

science section 4

unification

recurring theme of great leaps forward in physics; two seemingly different phenomena can be explained by the same fundamental principle

what was the first great unifcation

newton’s laws of motion

another great unification

electricity and magnetism

what set of equations summarizes the connection between electricity and magnetism

maxwell’s equations

who made maxwell’s equations

james clerk maxwell

what equations makeup maxwell’s equations

gauss’s law for electric field, gauss’s law for magnetic field, faraday’s law, ampere’s law

what is gauss’s law for electric field

E = electric field

da = closed surface like a sphere, da is like a tiny arrow sticking out of the surface (tiny vector pointing outward)

q = charge

Eo = permittivity of free space

what is gauss’s law for magnetic field

B = magnetic field

da = tiny vector pointing outward

faraday’s law of induction

E = electric field

dl = A tiny piece of a path that has both a length and a direction, taken along a closed loop.

last term = rate of change of magnetic flux

ampere’s law

B = magnetic field

dl = same def from above

u thing = permiability of free space

I = current passing thru loop

last term = changing electric field/maxwell’s displacement current

gauss’s law for electric field describes

how an electric field is created around charge

gauss’s law for magnetic field describes

how a magnetic field is created around moving charges.

why does magnetic field equation equal 0

its impossible to draw a closed surface thru which there is a non-zero magnetic flux. no individual magnetic charges, only dipoles

what does faraday’s law expalin

changing magnetic field gives rise to an electric field

amperes law says

electric current (or any changing electric field), gives rise to a magnetic field

what is maxwell’s displacement current (equation)

changing electric field between plates of a discharging capacitor

maxwell was the first person to do what

write out all the ideas in a rigorous mathematical form and explicitly define what is meant by an electric and/or magnetic “field” in the form of an equation

james clerk maxwell was a

theoretical physicist

describe the electric field of a proton when it moves

when the proton is stationary, the electric field will point away from it. proton moves to new position and electric field will now be pointing away from the new position. for this to happen, the field next to the proton will change first and then the field at points further and further away will change in succession

analogy for electric field of moving proton

duck (proton) moving back and forth in water causing ripples (propogate outward like electric field) in the water. more quickly the duck moves back and forth = closer wave crests will be together

how to make electromagnetic wave

proton moves back and forth —> electric field switches back and forth —> magnetic field switch back and forth

our bodies can detect what through what

changing electric and magnetic fields through our eyes

the color red has a frequency of

400 trillion times per sec

yellow

500 trillion times per sec

green

600 trillion times per sec

blue

700 trillion times per sec

light is an

electromagnetic wave

maxwell took the unification of electricity and magnetism and unified them both with

the physics of light

what three things can light do

make a rainbow, reflect your image, make a straw look bent in water

if you manipulate maxwell’s equations correctly you get an equation that describes

wave motion

what are the speed of the electromagnetic waves (speed of light)

3×10^8 m/s

speed of light was measured by

astronomers

maxwell was the first to truly know

the nature of light

astronomers were able to measure the speed of light by

noting the delay in observations of jupiter’s moons depending on where Jupiter was in its orbit

a wave is how we describe

the transference of energy thru a substance without any of the substance itself being transported (ripples carry energy of impact but after wave passes, water itself is in same position as it was before)

longitudinal wave

material move back and forth in same direction as the wave

what is a what is b

a) longitudinal wave

b) transverse wave

example of longitudinal wave

sound: vocal chords vibrate back and forth —> air nearby vibrates back and forth —> air next to that vibrate, and so on until air in someone’s ears start to vibrate

power plant sends vibrations of electrons to your home rather than electrons themselves

transverse wave

direction of vibration is perpendicular to the direction of the wave

examples of transverse waves

guitar string plucked, “the wave” at sports stadium (people stand up, but direction of wave moves right/left)

lambda

wavelength (peak to peak) (trough to trough)

sound wave amplitude is

loudness of sound

light wave amplitude

brightness of light

amplitude describes the

instensity of the wave which is measured in diff units depending on type of wave

we can also describe a wave with a

sense of time

wave frequency (f)

how many full wavelengths pass through a given point per sec

frequency of wave is measured in

hertz (1 hertz = 1 wavelength per sec)

velocity

wavelength * frequency (measured in m/s)

speed of sound waves in air

300 m/s (760 mph)

speed of light in m/s

300 mill m/s

which is faster light or sound

light (by a million)

sound is a wave that passes through a

substance

sound is the vibrtaion of a (blank) so if there is no (blank), there will be no sound

substance (for both)

(blank) cannot travel through a vacuum of space but (blank) can

sound; light (variation of electric and magnetic fields)

how many miles of vacuum between the sun and earth

100 mill miles

electromagnetic waves travel across the universe for (blank) of years to end their journey in our eyes

billions

speed of light is a (blank) usually represented as 

constant; c

knowing speed of light is a constant what is that helpful with

if we know the wavelength, we can find the frequency and vice versa

wavelength and frequency have a (blank) relationship

inverse

high-frequency wave will have a (blank) wavelength

short wavelength

wavelengths of the colors

any visible color not in the rainbow is a

comibantion of colors

white has

no single wavelength but is a combination of multiple wavelengths added on top of each other

black is the

absence of any light at all

wavelengths of visible spectrum range from

400 nm (blue) to 700 nm (red)

nm = nanometers

the given numbers for wavelengths are (blank) because they gradually

arbitrary; fade into each other

high wavelength, low frequency to low wavelength, high frequency in order

go longer in wavelength and lower in frequency than (color), we get

red; infrared

what is infrared

feel heat, don’t see

atoms of some objects such as (blank) or (blank) are vibrating fast enough to emit visible light waves

incandescent light bulb, toaster filament

(blank) in our environment gives off some infrared radition

everyhting

what are typically used in long-stance communication

microwave and radio wave

why are microwaves and radio waves used for long-distance communication

certain obstacles that are opaque to visible radiation are transparent to these waves —> phone still works even tho its surrounded by walls

(blank) blocks infrared while allowing (blank) to pass through giving rise to the (blank)

glass; light; greenhouse effect

wi-fi frequencies are in the (blank) part of the spectrum

microwave

microwave oven has a (blank) inside of it, which causes (blank) to emit (blank)

miniature particle accelerator; electrons; microwave radiation

microwave wavelengths are (large/small) compared to visible light, but they are still smaller than a (blank)

large; cm

what is the purpose of the holes behind the microwave door

they are small so the microwaves themselves don't get out so there is no danger to you

if you had the microwave door open what is the worst that can happen to you

youll feel hot from the radiation but no danger because of the normal use of microwave ovens

if you gathered enough wifi routers in a room, it would

cook anything inside just like a microwave oven, but you wouldn’t be able to fit enough routers in a room to generate that much heat

dangerous radiation is on what side of spectrum

UV, X-ray, gamma rays

ultraviolet radiation is most commonly associatedwith

getting a sunburn

sunblock contains chemicals that are good at

absorbing UV radiation

what can UV damage

skin cells, inks, dyes

uv radiation in outer space is much more (blank) than on earth’s surface

intense

american flag on moon is now

white

x-rays were discovered in (year) by (name) when he found that they were emitted by (blank)

1895; Wilhelm rontgen; electrons accelerated by high voltages

x-rays can pass through

atoms in the skin, mostly hydrogen and oxygen (water), but are absorbed by the large calcium atoms in bone

first x-ray photo was of

rontgen’s wife’s hand

what makes x-rays damaging

the dose

gamma rays typically come from

atomic nuclei that are undergoing radioactive decay (nuclear fallout)

everyhting from UV and beyond is referred to as

ionizing radiation

ionizing radiation

radiation capable of breaking apart atoms within human body

there are diff kinds of radiation but there is fundamentally (blank) between gamma rays, radio waves, color blue

no difference

radiaiton is (blank) for life

necessary

unless you (blank) or (blank), you are not likely to encounter dangerous levels of ionizing radiation

go to space; wander into a nuclear reactor

electric and magnetic fields point (blank) to the direction of the wave

perpendicular

we choose the (blank) component of the wave to be the main direction of the oscillation of the wave. why? what is this called?

electric field; because electric charges are the origin of the waves; wave polarization

if electric field component of wave oscialltes int he +x and -x direction it is polarized in the

x direction

if polarized in the x direction, the wave is

transverse since the direction of vibration is perpendicular to the direction of the wave