Class Five

Question 1

what is direct current

Answer 1

current flows in one direction

Question 2

what is alternating current

Answer 2

when the direction of current changes → electrons are constantly shuttling back + forth

Question 3

RMS voltage formula

Answer 3

V max / √2

Question 4

magnetic fields are created by..

Answer 4

moving electric charges aka electric current

Question 5

magnetic force formula

Answer 5

F_B = q(v x B)

v = velocity of charge

Question 6

magnitude of magnetic force equation

Answer 6

F_B = qvBsin∅

∅ = angle between v and B

Question 7

when do you use the right hand rule

Answer 7

when q is positive

Question 8

what is the right hand rule

Answer 8

point your thumb at direction of velocity

point fingers at direction of B

and so the direction of F_B will be perpendicular to your palm

Question 9

ammeters must be connected in..

Answer 9

series

Question 10

voltmeters must be connected in..

Answer 10

parallel

Question 11

what is periodic/harmonic motion

Answer 11

any motion that regularly repeats

Question 12

what is a period

Answer 12

time it takes an object to move through one full cycle of motion

Question 13

what is frequency

Answer 13

the number of cycles that occur in one second

Question 14

period and frequency relationships

Answer 14

frequency = 1/period

period = 1/frequency

Question 15

Hooke’s law

Answer 15

F = -kx

springs exert a force on a block that is proportional to its displacement

k = spring constant (how strong it is)

Question 16

elastic potential energy formula

Answer 16

PE_elastic = ½kx²

Question 17

what is the amplitude

Answer 17

maximum displacement of a block from equilibrium

Question 18

what is a mechanical wave

Answer 18

series of disturbances within a medium that transfers energy from one place to another

Question 19

electromagnetic waves do not need..

Answer 19

a medium

Question 20

wave equation

Answer 20

v = velocity

length of a wavelength

f = frequency

Question 21

the speed of a wave is determined by the..

Answer 21

type of wave and the characteristics of the medium, not by the frequency

Question 22

when a wave passes into another medium..

Answer 22

its speed changes but its frequency does not

Question 23

wavelength is proportional to

Answer 23

wave speed

Question 24

what is interference of waves

Answer 24

when 2 or more waves are superimposed on eachother → forms a single resultant wave

Question 25

waves that are in phase with eachother

Answer 25

when crest meets crest and trough meets trough their amplitudes add

Question 26

what happens to amplitudes to waves in phase with eachother

Answer 26

they add

Question 27

waves out of phase

Answer 27

crest meets trough amplitudes subtract

Question 28

what happens to amplitudes of waves out of phase

Answer 28

they subtract

Question 29

if the path difference = nλ and n = 1,2,3 then..

Answer 29

the waves will be in phase and will constructively interfere

Question 30

if the path difference = (n + ½)λ, the waves will be 180 degrees out of phase and..

Answer 30

will therefore destructively interfere

Question 31

what are nodes

Answer 31

points of no displacement

Question 32

what are antinodes

Answer 32

halfway between 2 nodes where amplitude is maximized

Question 33

standing wave wavelengths for 2 fixed ends

Answer 33

2L/n n = harmonic number

Question 34

standing wave frequencies for 2 fixed ends formula

Answer 34

n/2L (v)

Question 35

how much work do magnetic fields do

Answer 35

zero

Question 36

transverse vs longitudinal waves

Answer 36

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

Question 37

sound waves are a type of..

Answer 37

longitudinal wave

Question 38

sound travels the slowest through ___ and faster through \_\_\_

Answer 38

slow: gases fast: solids

Question 39

speed of sound depends on 2 things

Answer 39

medium's resistance to compression and density

Question 40

why do beats occur

Answer 40

2 waves with different frequencies

Question 41

beat frequency formula

Answer 41

f1-f2 difference between the frequencies of the 2 original sound waves

Question 42

what is the intensity of a sound wave

Answer 42

the energy it transmits per second per unit area

Question 43

intensity level in decibels formula

Answer 43

10log₁₀(I/I_o)

Question 44

everytime we multiple I by 10..

Answer 44

we add 10 to B

Question 45

everytime we divide I by 10..

Answer 45

we subtract 10 from B

Question 46

Doppler effect

Answer 46

arises when a source of waves is moving relative to the detector

Question 47

Doppler effect formula

Answer 47