Edexcel A-Level Physics 9PH0
Working as a Physicist
Mechanics
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Materials
Waves and Particle Nature of Light
Further Mechanics
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Thermodynamics
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Thermodynamics
Black body radiation and Wien's law
- 1 thing to know
- Papers 2 and 3
Overview
Recall questions on what a black body radiator is, the shape of the radiation curve and how it changes with temperature, and Wien's law applied to a star.
What you need to know
Answer each one before you reveal it.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is meant by a black body radiator?
Model answer
It is a body that absorbs all the electromagnetic radiation falling on it and is also the best possible emitter of radiation at every wavelength.
- 2
Why is the radiation from a black body described as a continuous spectrum?
Model answer
It emits at every wavelength rather than at separate discrete wavelengths, so the intensity varies smoothly across the spectrum.
- 3
What shape does the radiation curve for a black body have?
Model answer
The intensity rises from almost zero at very short wavelengths to a single peak, then falls away more gradually at longer wavelengths without reaching zero.
- 4
How does the radiation curve change as the temperature of the black body is increased?
Model answer
The peak shifts to a shorter wavelength and the intensity rises at every wavelength, so the area under the curve becomes much larger.
- 5
Can the radiation curves for two different temperatures ever cross?
Model answer
No, because the curve for the higher temperature lies above the other at every single wavelength.
- 6
State Wien's law:
Model answer
Wien's law is λₘₐₓT = 2.898 × 10⁻³ m K.
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