Class Five Flashcards
what is direct current
current flows in one direction
what is alternating current
when the direction of current changes → electrons are constantly shuttling back + forth
RMS voltage formula
V max / √2
magnetic fields are created by..
moving electric charges aka electric current
magnetic force formula
FB = q(v x B)
v = velocity of charge
magnitude of magnetic force equation
FB = qvBsin∅
∅ = angle between v and B
when do you use the right hand rule
when q is positive
what is the right hand rule
point your thumb at direction of velocity
point fingers at direction of B
and so the direction of FB will be perpendicular to your palm
ammeters must be connected in..
series
voltmeters must be connected in..
parallel
what is periodic/harmonic motion
any motion that regularly repeats
what is a period
time it takes an object to move through one full cycle of motion
what is frequency
the number of cycles that occur in one second
period and frequency relationships
frequency = 1/period
period = 1/frequency
Hooke’s law
F = -kx
springs exert a force on a block that is proportional to its displacement
k = spring constant (how strong it is)
elastic potential energy formula
PEelastic = ½kx2
what is the amplitude
maximum displacement of a block from equilibrium
what is a mechanical wave
series of disturbances within a medium that transfers energy from one place to another
electromagnetic waves do not need..
a medium
wave equation
v = velocity
length of a wavelength
f = frequency
the speed of a wave is determined by the..
type of wave and the characteristics of the medium, not by the frequency
when a wave passes into another medium..
its speed changes but its frequency does not
wavelength is proportional to
wave speed
what is interference of waves
when 2 or more waves are superimposed on eachother → forms a single resultant wave
waves that are in phase with eachother
when crest meets crest and trough meets trough
their amplitudes add
what happens to amplitudes to waves in phase with eachother
they add
waves out of phase
crest meets trough
amplitudes subtract
what happens to amplitudes of waves out of phase
they subtract
if the path difference = nλ and n = 1,2,3 then..
the waves will be in phase and will constructively interfere
if the path difference = (n + ½)λ, the waves will be 180 degrees out of phase and..
will therefore destructively interfere
what are nodes
points of no displacement
what are antinodes
halfway between 2 nodes
where amplitude is maximized
standing wave wavelengths for 2 fixed ends
2L/n
n = harmonic number
standing wave frequencies for 2 fixed ends formula
n/2L (v)
how much work do magnetic fields do
zero
transverse vs longitudinal waves
transerve: direction of the medium particles is perpendicular to the direction the wave travels
longitudinal: direction of the medium particles is parallel to the direction the wave travels
sound waves are a type of..
longitudinal wave
sound travels the slowest through ___ and faster through ___
slow: gases
fast: solids
speed of sound depends on 2 things
medium’s resistance to compression and density
why do beats occur
2 waves with different frequencies
beat frequency formula
f1-f2
difference between the frequencies of the 2 original sound waves
what is the intensity of a sound wave
the energy it transmits per second per unit area
intensity level in decibels formula
10log10(I/Io)
everytime we multiple I by 10..
we add 10 to B
everytime we divide I by 10..
we subtract 10 from B
Doppler effect
arises when a source of waves is moving relative to the detector
Doppler effect formula
