PHYS1006 Lecture Notes - Lecture 18: Work Function, Sunburn, Mercury-In-Glass Thermometer
25 Jun 2018
School
Department
Course
Professor
Zia Palmer
PHYS1006
Atomic and Nuclear radiation
Early Quantum Theory and Models of the Atom
Learning outcomes:
Planck’s Quantum Hypothesis
EM radiation emitted by hot objects
Photoelectric Effect
Bohr model of the hydrogen atom
Atomic Physics
In the early 20th century two new developments in physics revolutionised our
understanding of nature.
1. The theory of relativity.
2. Quantum theory.
Blackbody Radiation
All objects emit radiation whose total intensity is proportional to the fourth power
( of their Kelvin temperature.
A body that emits ALL radiation when hot, is called a blackbody.
A blackbody would also absorb all radiation that is incident on it and will reflect
none, therefore appearing ‘black’.
The sun is a blackbody even though it is not necessarily black in colour.
A hot oven element or glowing filament of a light globe may also be considered a
blackbody radiator.
Quantum Physics
Consider a hot pizza oven at temperature . Measure the intensity and wavelength of
radiation emitted from a small hole in the oven. The plot of intensity vs is called the
spectrum of blackbody radiation.
1. The total power of the emitted radiation increases as increases.
Stefan – Boltzmann Law
is the total power of emitted radiation
is 1, a perfect radiator: blackbody
the Stefan-Boltzmann constant:
is the surface area of an object
is the temperature in Kelvins (K)
2. The peak of the spectra shifts towards shorter as increases.
Wein’s Law
Example 1
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A tungsten filament lamp is operating at 2230C. The surface area of the filament is and .
Assuming the surrounding temperature is 20C what is the power output of the filament
and the at peak intensity.
Information we have:
is the Stefan-Boltzmann constant:
the surface area is
is given as 0.30.
Important – temperature is given in C so therefore needs to be converted to Kelvins (K).
is
Wavelength at peak intensity – Wein’s Law
Referring to the plot of intensity vs it can be concluded that the max intensity is emitted in
the infrared radiation part of the spectrum
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Early quantum theory and models of the atom. In the early 20th century two new developments in physics revolutionised our understanding of nature: the theory of relativity, quantum theory. All objects emit radiation whose total intensity is proportional to the fourth power ( of their kelvin temperature. A body that emits all radiation when hot, is called a blackbody. A blackbody would also absorb all radiation that is incident on it and will reflect none, therefore appearing black". The sun is a blackbody even though it is not necessarily black in colour. A hot oven element or glowing filament of a light globe may also be considered a blackbody radiator. Consider a hot pizza oven at temperature . Measure the intensity and wavelength of radiation emitted from a small hole in the oven. The plot of intensity vs is called the spectrum of blackbody: the total power of the emitted radiation increases as increases.
