Physics - Waves

transverse wave example

transverse wave example

light waves (electromagnetic waves)

Energy transfers .... not .....

energy, matter

electromagnetic waves

ultra violet
infa-red
gamma
radio
x-rays
visible light
microwaves

electromagnetic wave with the highest frequency and the shortest wave length

gamma rays

electromagnetic wave with the lowest frequency ad longest wave lenght

radio waves

frequency

the number of waves that pass a given point per second

Wavelength

the distance from one point on the wave to the very same point on the next wave

what is wavelength measured in?

meters (m) and expressed in lambda (λ)

crest/peak

the top of a transverse wave

trough

bottom of a transverse wave

amplitude

the distance from the peak of the wave to the equilibrium line

Rarefraction

the section of a longitudinal wave where the particles are spread/stretched out

Compression

the section of a longitudinal wave where the particles are close together/compressed.

v = x/t

velocity=displacement/time

s = d/t

speed=distance/time

v = fλ

wave speed = frequency x wavelength

f = 1/T

frequency = 1/period

period

the time it takes for a complete wave to pass

Reflection

the bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through

the normal

an imaginary line perpendicular to the surface

refraction

The bending of a wave as it passes at an angle from one medium to another - it happens because light changes speed in a substance with different densities

the denser the substance...

...the slower the light ray travels

the less dense the substance...

...the faster the light ray travels

Diffraction

The bending of a wave as it moves around an obstacle or passes through a narrow opening

r = vt

??

I = (E/t)/area

Intensity = Power(Energy/Time)/area

n = Sin(i)/Sin(r)

refractive index = angle of incidence/angle of refraction

n = c / v

Refractive index = speed of light/speed of light in a medium


refractive index of a substance, it is a ratio so has no units. It tells us how fast light travels in that material compared to how fast light travels in a vacuum.

Snell's Law

n1/n2 = SinØ2/SinØ1

first material/second material = Ø Refraction/Ø Incidence

total internal reflection

when a light ray is reflected inside a material

Øc = critical angle

When light hits a boundary and travels along the boundary at 90 degrees to the normal

Expression for the critical angle

n1/n2 = Sin90/SinØc

NB. Sin90 = 1

∴ n1/n2 = 1/SinØc

What happens to angles of incidence bigger or smaller then the critical angle (Øc) ?

Bigger = Reflect and cause total internal reflection
Smaller = Refract

How does amplitude effect sound waves?

Higher amplitude = louder sound
Lower amplitude = softer sound

How does frequency effect sound waves?

Higher frequency = higher pitch
Lower frequency = lower pitch

Can sound waves travel in a vacuum?

No, sound waves must have a medium/molecules to travel

What state of matter does sound travel faster in?

solid because the particles are touching making it easier for the waves to travel - vibrations are more easily passed from particle to particle

human hearing range

20 Hz to 20 000 Hz

sounds below 20 Hz

infrasound

Sounds above 20 000 Hz

ultrasound

Decibels

a measure of how loud a sound is

Superposition

the displacement of a wave (the one you see) is the algebraic sum if the individual waves

standing waves

the superposition of 2 waves with the same wavelength, amplitude and frequency moving in the opposite direction.

The wave appears to not move.

nodes

- the point that destructive interference happens
- they don't move
- one wavelength between each node

Antinode

the peak of the standing wave

harmonics

standing waves are described in terms of harmonic depending on how many 'loops' they have. The most simple harmonic is the first harmonic and it has the fundamental frequency (lowest) and the longest wavelength. All other harmonics have frequencies which are multiples of the first harmonic.

What is frequency measured in?

Hertz (Hz)

Ray and wavefront

A ray shows the direction of a wave/the movement of energy and a wave front is perpendicular to the ray

displacement-distance graph vs displacement-time graph

The displacement-time graph illustrate the displacement of an object over time (T = period) whereas the displacement-distance graph tell the position of the vibrating particles of a wave (λ).

interference of waves

the way in which the waves combine

Longitudinal waves definition

the direction of energy(travel) is parallel to the oscillation(vibrations) of the particles

longitudinal wave example

sound waves

transverse wave definition

the direction of the energy(travel) is perpendicular to the oscillation(vibrations) of the particles.

what are two types of interference that happen during superposition?

Destructive: When the waves are opposites
Constructive: When the waves are the same

oscillation

act of swinging back and forth (vibrations)