Waves

Question 1

displacement (X) (oscillations)

Answer 1

instantaneous distance from the equilibrium position in a specific direction (m)

Question 2

amplitude (Xo) (oscillations)

Answer 2

maximum displacement from the equilibrium position (m)

Question 3

frequency (f) (oscillations)

Answer 3

number of oscillations per second (Hz)

Question 4

period (T) (oscillations)

Answer 4

time for one oscillation (s)

Question 5

phase (oscillations)

Answer 5

measure of how “in step” different particles are (one cycle = 360 degrees or 2 pi radians)

Question 6

Definition of Simple Harmonic Motion (SHM)

Answer 6

SHM is a type of oscillation that takes place when the acceleration of (and force on) an object is:

• proportional to its displacement from the equilibrium position
• in the opposite direction to the displacement (i.e. towards equilibrium position)

Question 7

Longitudinal Waves

Answer 7

the particles in the medium vibrate parallel to the direction of the energy transfer

Question 8

Transverse Waves

Answer 8

the particles of the medium vibrate at right angles to the direction of energy transfer

Question 9

Displacement (waves)

Answer 9

distance the medium has moved from the equilibrium position in a particular direction (m)

Question 10

Frequency (f) (waves)

Answer 10

number of oscillations of the medium (or complete waves passing a point) per second (Hz)

Question 11

Period (T) (waves)

Answer 11

time for one complete oscillation of the medium (or time for one complete wave to pass a given point) (s)

Question 12

Wavelength

Answer 12

shortest distance between two points that are in phase along a wave, e.g. crest to crest (m)

Question 13

Wave Speed

Answer 13

distance travelled per unit time by the energy of the wave (or by wavefront) (m/s)

Question 14

Amplitude (A) (waves)

Answer 14

maximum displacement of the medium from the equilibrium position (m)

Question 15

Intensity Definition

Answer 15

power per unit area received by an observer

Question 16

Mechanical Wave

Answer 16

requires a medium to travel through

Question 17

Electromagnetic Waves

Answer 17

do not require a medium to travel through
all EM waves are transverse
travel at 3 X 10^8 m/s in a vacuum/air

Question 18

Relative Wavelengths of EM Waves

Answer 18

radio waves: 10^2 m 
microwaves: 10^-3 m
infrared: 10^-5 m
visible light: 10^-7 m 
ultra violet: 10^-9 m 
x rays: 10^-12
gamma rays: 10^-14

Question 19

Conditions for Total Internal Reflection

Answer 19

• light is travelling from a more to a less optically dense medium
• the angle of incidence is greater than the critical angle

Question 20

Diffraction

Answer 20

when the waves move past an obstacle or through a gap the waves tend to spread out, this spreading out is called diffraction

Question 21

Principle of Superposition

Answer 21

“if two or more waves meet, the resultant displacement at any point is found by adding the displacements produced by each individual wave”

Question 22

Anti nodal lines (interference)

Answer 22

• waves meet in phase
• constructive interference
• path difference = n x wavelength
• maximum amplitude
• “maxima”
• bright light or loud sound

Question 23

Nodal lines (interference)

Answer 23

• waves meet out of phase
• destructive interference
• path difference = (n+1/2) x wavelength
• zero amplitude
• “minima”
• dark light or quiet sound

Question 24

Conditions for Standing Waves to Form

Answer 24

waves must be:

• of the same amplitude
• of the same frequency
• travelling in opposite directions

Question 25

Summary of Standing Waves

Answer 25

• strings and pipes have a range of resonant frequencies (harmonics) at which they will form standing waves
• strings and open pipes can produce all harmonics
• closed pipes can only produce odd-numbered harmonics

Question 26

Polarisation Definition

Answer 26

if an EM wave such as light is polarised, the electric field vector is oscillating in one plane only

Question 27

Brewster’s Law

Answer 27

when light reflects off a surface it will be polarised in the plane of the surface
the angle between the reflected and refracted ray has to be 90 degrees for polarisation to be 100%

Question 28

Malus’ Law

Answer 28

polarising filter restricts the electric field vector of EM waves passing through it to a direction perpendicular to the embedded crystal chains
an analyser is a device that can detect polarised light, if the angle between the polarisation of the incident light is 0-90 then some light will pass through. If it = 90 then no light passes through.
if unpolarised light passes through a polariser, the light intensity will be reduced by half

Question 29

Interference and Polarisation

Answer 29

two waves must have the same plane of polarisation in order to produce an interference pattern
waves of different polarisation cannot cancel or add they just create a wave of a different plane of polarisation