Lecture 3: Waves, Didfraction , Light Waves

Wavelength, frequency, and speed are related

λv = s

Vertical displacement vs. position

Y(x) = Asin (2pi/ λx)

Constructive interference

When two waves are in phase so they combine to create a bigger wave

Destructive interference

When two waves are out of phase and they create a straight line

Fourier transform

A signal in the time domain can be represented in the frequency domain

Diffraction proves

The wave -like nature of light

Interference in time

Waves of differing frequency

Interference in space

Waves originated from same source wave

Period equation

T= 1/v

What determines an elements chemical reactivity and material properties

The electrons in the atom

Why did quantum mechanics develop

To explain phenomena (like atomic stability and emission spectra ) that classical physics couldn’t

List four key premises of quantum mechanics

1) energy is quantized (not continuous ).

2) particle can behave like waves

3) particle waves can superpower to form new states

4) there are fundamental limits to measuring certain properties simultaneously

Relationship between wavelength, frequency, and speed ?

λv = s (for light in vacuum, v = c = 3.0 × 10^8 m/s)

Define amplitude, wavelength, frequency and period

Amplitude : maximum displacement

Wavelength : distance for one full cycle

Frequency : cycles per second

Period : time for one cycle (T= 1/v)

What is a wave vector k

K = 2pi / wavelength , relates spatial variation of wave

What is constructive interference

Waves in phase, add to increase amplitude

What is destructive interference

Waves out of phase by pi cancel each other

What does a Fourier transform show

How a signal in time domain is represented in frequency domain

What experimental demonstrates lights wave nature

The double slit interference experiment

What happens to the two slit when wavelength increases ?

Fringe spacing increases

How does diffraction prove light behaves as wave

Diffraction patterns arise only from wave interference

How are EM waves generated

Oscillating charges create perpendicular electric and magnetic fields that propagate outward

Key equation for EM? Waves

Wavelength ( frequency ) = c (speed of light )

Name the regions of the electromagnetic spectrum from low to high frequency

Radio → microwave → infrared → visible → ultraviolet → x-ray → gamma ray→

What is black body?

An ideal object that absorbs all incident radiation and emits only thermal radiation

How does temperature affect emitted radiation ?

Higher temperature → faster particle motion → higher frequency (shorter wavelength ) radiation (color shifts red → orange → white )

Give examples of diffraction or interference in daily

Soap bubbles, iridescent animal coloring, deli meat sheen

How is diffraction used in research

Determining molecular structures

Bohr model shortcoming