Physics- Longitudinal and Transverse waves

In mechanical waves, particles _______ about a fixed point

oscillate

oscillate definition

Rapidly moving back and forth between two points

What is a progressive wave?

Oscillations that transfer E and info

Transverse wave definition

A wave in which particles oscillate perpendicular to the direction of wave of travel (and E transfer)

e.g. of transverse waves

electromagnetic waves (radio, visible light, UV)

Can transverse waves be polarised

yes

polarised in waves defintion

When waves are polarized, their oscillations occur in a single plane. This means that the waves vibrate in a specific direction, perpendicular to the direction of wave propagation

Longitudinal waves definition

A wave in which particles oscillate parallel to direction of wave travel (+ E transfer)

e.g. of longitudinal waves

sound and ultrasound waves

Can longitudinal waves be polarised?

No

What is displacement in waves and what axis is it usually on?

Distance of point on wave from equilibrium position

Y-axis

Wavelength definition and symbol

Distance between points on successive oscillation of wave in phase

Greek letter lambda (λ).

amplitude definition

max displacement of particle in wave from equilibrium position

how to measure wavelength is longitudinal waves

distance between 2 compressions/ rarefactions

what is period/ time period ?

time taken for one complete oscillation or cycle of wave

what is frequency ?

n. of complete oscillations/ wavelengths passing a point her unit time

what is wave speed?

distance travelled by wave per unit time

Phase definition

how far the cycle of one point is compared to another point on the same wave

what does phase tell us

how much a point/ wave is in front/ behind another

When are waves in phase?

when relative crests/ troughs are aligned

Is 360

When are waves in antiphase?

when crest of one wave allinges with trough of another

is 180

how to convert λ to degrees and radian

X by 360 / 2π

What is a CRO and its full name?

Cathode- Ray Oscilloscope

Lab instrument used to display, measure and analyse wavefront of electrical circuits

Using wave speed equation for wave of constant speed if:

• Wavelength increases = frequency decreases

• Wavelength decrease= frequency increase

What are compresssions?

Areas of high pressure due to particles being close together

What are rarefractions?

Areas of low pressure due to particles spread further apart

What is intensity in waves?

Amount of energy passing thru a unit of area per unit time / power per unit area

Intensity unit

Watts per metre squared, Wm^-2

What is Intensity proportional to?

Amplitude squared and frequency squared

What are spherical waves?

Wave from a point source which spreads out equally in all directions

What is the area spherical waves move through?

Surface area of a sphere: 4πr²

Does intensity increase or decrease as spherical wave through increasing distance from source?

Decreases (assuming there is no absorption)

Intensity is also proportional to _____ in spherical wave

1/r²

distance travelled by a wave in 1 oscillation is = to

wavelength

If two waves have same frequency they also have same ____

time period

how to find phase difference in degrress

360 x d/λ

d=- distance between two points

ever ___ of a n osculation in standing waves they have 0 displacement

1/4

stationary waves need to hace the same ___ to form

frequency

stationary waves are in a constant _____ _____

phase relationship

coherent waves are waves with:

• constant phase relationship

• same frequency

coherent waves produce a _____ interference pattern

stable

what is a stable interference pattern

contain fixed positions of constructive and destructive interference

way to create stable interference pattern

• stationary wave

• coherent waves travelling in opposite directions or they cross at a point

monochromatic light

continuous stream of oscillations of the electromagnetic field at a single frequency

how to find distance between slits in a diffraction grating

d= L/ n

d= distance

L= length along the grating

n= the n. of lines

amplitude is inversely proportional to what

distance

what does an oscilloscope show and what can this be used to work out?

time period

frequency

how can you find refractive index using the critical angle method

Another critical angle equation

SinC= n2/n1

how can you demonstrate in lab that light is plane polarised

• Use a polaroid / polarising filter

• Rotation of this will change the intensity (of the light)

if working out distance of refracted wave from depth use

work out it with trig using angle

show that the speed v of the wave is given by the equation v = fλ

• v=s/t

• Since distance is  and time is : v=λ/ T

• as T=1/f

• therefore v=fλ

phase difference

phase difference = time t for the two rays to travel between the dashed lines X and Y x 360/ period T of the light wave

Constructive interference is only possible when the phase difference is __

a whole n. of wavelengths

tubes closed at one end only have _____-numbered harmonics

odd i.e. 1st, 3rd, 5th etc

SHM Equation: 

equation used in diffraction grating equation (learn)

nλ= dSinθ

n=order of diffraction pattern (use heights n.)

d= distane between slits (m)

θ= normal to maxima angle

How to work out distance between slits, d

d=1/N

N= n. of slits per m

What do each “axes” on an oscilloscope measure?

Vertical divisions= voltage/ amplitude of wave

Horizontal divisions= time

Can a wave be both refracted and reflected at a boundary?

Yes, at low angle of incidence most will be refracted, but some will reflect

Superpose definition

2 waves in the same place combining

Coherence definition:

Coherent waves have same frequency and wavelength and a fixed phase difference

Path difference v phase difference

Path difference: difference in distance that two waves have travelled in terms of wavelength ( units of length)

Phase difference: difference in the point in the cycle of two waves as a proportion of a full wave cycle ( units of degrees/ radians)

What is youngs double slit experiment?

A single source of light directed towards a double slit, which creates 2 coherent beams of light. This intereferes as it hits the screen and creates an intereference pattern

What is the impact of increasing slit width?

Increases width of the central diffraction maximum

units of λ=ax/D

λ- wavelength

a- slit spacing

x- fringe

d- distance to screen

What 2 properties can be explained if light is a wave?

• Diffraction

• Interference

What is a stationary wave?

Consists of alternating fixed pattern of nodes (0 amplitude + no vibrations ) and antinodes (points of max amplitude). No energy is transferred across the wave

Similarity and difference between stationary and progessive waves

S: Both have wavelength, frequency and amplitude

D: stationary waves don’t transmit energy from one place to another

What is meant by harmonics ?

Points where stationary wave form doesn’t change beacuse the waves in each direction are reinforce each other

How many nodes and antinodes does 1st harmonic have?

Nodes- 2 (1 at either end)

Antinodes- 1 (in the middle)