Physics 3 (waves, sound and light)

What is a wave

A disturbance that travels from one place to another transporting energy, but not necessarily matter, along with it.

Energy of a wave

the amount of energy in a wave corresponds to the amplitude of the wave; more amplitude = more energy

Energy is proportional to amplitude squared.

Longitudinal and transverse waves

Longitudinal
particle movement is parallel to the direction of wave propagation

Transverse
particle movement is perpendicular to the direction of wave propagation

wavelength

The distance between two crests

period

time taken to get from one crest to another

frequency

the number of complete wavelengths that pass a point in a given time

frequency = 1 divided by the period
frequency measured in Hertz
1Hz is 1 wave cycle per second. 2Hz is 2 wave cycle per second.

speed of wave

how far the wave travels in a given amount of time

wavelength x frequency

sounds waves are

longitudinal waves.

In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. They molecules pass the vibrational energy to each other which transmits the sound.

sound waves need a medium to propagate. Sound waves have different speeds depending on which medium they travel through because some mediums are more easy to propagate than others. Denser mediums are easier to propagate because the atoms are closer together so can pass on vibrational energy quickly.

attenuation

energy loss

sound of wave

larger amplitude = larger sound

Loundness of sound

loudness of sound is determined by the power density of the wave


power density = power at source/ surface area of a sphere

describe powe density logarithimically

10 times more power = 10 more decibel

power density in decibels

power density/ 10 to the -6W per cm2

brownian motion

the chaotic movement of colloidal particles, caused by collision with particles of the solvent in which they are dispersed.

Lecture 2 10/11/20

waves, sound and light part 3

wave front

A line representing the crest of a wave in two dimensions that can show the wavelength, but not the amplitude, of the wave when drawn to scale

angle of incidence

the angle between the incident ray and the normal

Two types of reflection

1. specular (regular)
when you're reflecting of a smooth surface

2. diffuse (irregular)
when you're reflecting of a rough surface

law of reflection

the angle of incidence is equal to the angle of reflection

refraction

the bending of a light waves at the interface between two materials.

Due to refractive index - different materials have different refractive indexes.

refractive index equation

Speed of light in a vacuum/Speed of light in the medium

n = c/v

Snell's Law of Refraction

States that the product of the index of refraction of a medium and the sine of the angle of incidence equals the product of the index of refraction of a second medium and the sine of the angle of refraction.


If n2 bigger than n1 = ray bends towards the normal
If n1 bigger than than 2 = ray bends away from the normal

angle of left eye

aL - bL = bL - aL

angle of right eye

aR - bR = bR - aR

distance to object

d = o.5S x tanbL

s in cm
d in m

Lecture 3 17/11/20

light waves and photons

light

400-700nm

do longer wavelength diffract more or less?

more

constructive interference

The interference that occurs when two waves combine to make a wave with a larger amplitude.

destructive interference

The interference that occurs when two waves combine to make a wave with a smaller amplitude

rayleighs principle

The Rayleigh criterion is the generally accepted criterion for the minimum resolvable detail - the imaging process is said to be diffraction-limited when the first diffraction minimum of the image of one source point coincides with the maximum of another

The smallest thing that we can resolve in an image or picture can be no smaller than approximately half of the smallest wave length amongst the interfering waves. - rayleighs principle tells us what the fundamental limit to resolution is

the camel shape hump graph thing

other things that limit resolution
1. some optical elements will clip the size of the light beam that goes through it which causes distortion which reduces resolution

photons

particles of light

light of frequency f has photons of energy
E = hf (per photon)
Energy = planks constant x frequency of light

planks constant = 6.6 x 10 to the -34 Joules per second

frequency of light is proportional to the energy of each photon

intensity of light is proportional to the number of photons per time interval

radiation protection

photons of a short wavelength are more dangerous that photons of a larger wavelength - shorter wavelengths have higher energy and can radiate material

Sun emits UV radiation so for us to survive on earth we have to have a form of protection, this protection is called the ozone layer. Ozone layer absorbs a lot of the UV radiation.

two types of photoreceptors

1. rods
very sensitive, can detect single photons but not their colour


2. cones
three types of cones, sensitive to red, green, blue light range of wavelengths.


no signal sent to brain unless about 5-9 receptors are being stimulated simultaneously.