Quantum Mechanics Flashcards
EMR
Electromagnetic Radiation (EMR) is emitted by all objects and systems with a peak wavelength that depends almost entirely on temperature of the object
Higher temps - higher frequency
Wiens Law Equation
Wien found that peak wavelength at which an object will emit maximum intensity of radiation is dependant on surfact temperature
peak wavelength where max intensity of radiation is emitted = b (2.898 x 10-3) / T is the temperature of the object in kelvin (K)
Wien’s Law
An object at 1200K will emit its peak wavelength in the ultraviolet range
An obhect at 500K (our Sun) will emit its peak wavelength at approx 500nm
BlackBody Radiation
Wiens law is based on a theoretical object called a blackbody
A blackbody absorbs all EMR and therefore does not reflect any radiation - it may glow as though it emits all
Radiation emitted by an object can be approxiamated by the radiation emitted by a blakc at that same temperature
Peak Intensity
The spectrum is continous but has a peak intensity at a wavelength inversely porportional to temperature
max peaklength is inversaly proprtional to 1/T
One increases while other decreases at same rate
Re - Radiated EMR
Radiant energy interacts through reflection, transmission and/or absorption
Smaller molecules on Earth absorb very short wavelengths from the Sun
Larger molecules on Earth absorb larger wavelengths from the Sun
Lower layers of the atmosphere are predominantly heated by radiation from the Earth - must be emitted as infrared radiation
Links to Blackbody Radiation
Youngs Double Slit - Light as a Wave #1
The changing magnetic field will, in turn produce a changing electric field and the cycle will be repeated.
In effect, this produces two mutually propogating fields and the EMR is self-propogating - it can extend outward into space at the speed of light
Youngs Double Slit - Light as a Wave #2
Both the electric and magnetic fields oscillate at the same frequency; the frequency of the light wave
Forms of EMR include visible lights, infrared and UV radiation, radio waves, microwaves, X-rays and gamma rays
Youngs Double Slit - Light as a Wave Equation
v = wavelength (m) x frequency (Hz)
For light:
c = wavelength x frequency
Youngs Double Slit Experiment
Light was like plane waves and that as they passed through narrow slits, the plane waves were diffracted into coherent circular waves. Circular waves would interact causing interference.
Interference patten produced by the two waves would result in lines of constructive (antinodal) and destructive (nodal) intereference that matches the bright and dark fringes.
The Ultraviolet Catastrophe
When predicting the energy emitted by a body with really small wavelengths (UV radiation), it was found that it should approach infinity
Hence the idea was tweaked by Planck using experimental results and assumed light was emitted in discrete packets one energy called ‘quanta’
Plancks Equation
E = hf
where
E is the energy of a quantam of light (J)
f is the frequency of the EMR (Hz)
h is the constant 6.626 x 10-34
Light is often combined with Plancks equation
E = hc / wavelength
The Photon
All EMR is made up of photons
Evidence that light behaves as both a wave (Young’s Double Slit) and a particle (Planck’s equation)
Photons are always electrically neutral
Photons do not decay on thier own
Photons are massless (and ust travel at the speed of light)
The Photoelectric Effect
Noticed some types of EMR interacting with a piece of metal becoming positively charged
Charge is due to the ejection of electrons - known as photoelectrons
This is known as photoelectric effect and is reponsible for photocurrent
