Flashcards
2022-01-26
What simplifying model do we use when talking about emitters and absorbers of electromagnetic radiation??
Black bodies.
What two main assumptions are made about a black body??
- They are perfect emitters and absorbers of electromagnetic radiation
- They emit radiation at all wavelengths
Why is the sun yellow if it can be modelled as a near-perfect black body??
Because it is hotter than its surroundings and so is glowing.
What is special about how a black body emits radiation at all wavelengths??
It follows a standard curve.
What is on the $x$-axis for a black body curve??
Wavelength.
What is on the $y$-axis for a black body curve??
Intensity.
What does the area under a black body curve represent??
Luminosity.
Why do toasters glow red hot??
Because they are like a black body emitting E.M. radiation.
What is this??
A black body curve.
What does a black body curve show you??
The distribution of wavelengths emitted by a black body.
What happens to the position of the peak for a cooler object??
It will have a lower peak and move to the right.
What happens to the position of the peak for a hotter object??
It will have a higher peak and move to the left.
What does Wien’s displacement law state??
$$ \lambda_\text{max} \propto \frac{1}{T} $$
What law says that the peak wavelength emitted by an object is proportional to one over its temperature??
Wien’s displacement law.
What is the constant of proportionality in Wien’s displacement law, $\lambda_\text{max} \propto \frac{1}{T}$??
Wien’s constant.
Why is Wien’s displacement law, $\lambda_\text{max} \propto \frac{1}{T}$, useful??
Because it lets you work out the temperature of a star by measuring only its wavelength.
What does Stefan’s law state??
The total power radiated per unit surface area is directly proportional to the fourth power of the absolute temperature of black body.
What is Stefan’s law in equation form for $L$ in terms of radius, temperature and Stefan’s constant??
$$ L = 4\pi r^2 \sigma T^4 $$
What is Stefan’s law in terms of proportionality??
$$ L \propto T^4 $$
What law says that $L \propto T^4$??
Stefan’s law.
By combining Stefan’s law and Wien’s displacement law, what can you work out from just looking at starlight??
The radius of a star.
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date: 2022-01-26 18:56
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title: Physics - Black-Body Curves