Gustav Robert Kirchhoff

Wilhelm Wien

1824 –1887

Born Königsberg, Kingdom of Prussia

He coined the term "black body" radiation in 1862

1864 –1928

born at Gaffken near Fischhausen (Rybaki), Province of Prussia (now

Primorsk, Russia)
In 1896 Wien empirically determined a
distribution law of blackbody radiation,
later named after him: Wien's	11

Max Planck

•1858 –1947

•Planck was gifted when it came to music. He took singing lessons and played piano, organ and cello(Violoncello ), and

composed songs and operas. However, instead of music he chose to study physics.

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1-st Wien’s law (Displacement law)

Distribution of energy in an absolute Bb radiation spectrum is not homogeneous. It depends on the body temperature. Suppose:

T1 T2 T3

T1	T2	T3
B	B	B
	λ	m1 m2 m3
		λ
m1	m2	m3

There is one wavelength (λm) where radiant energy is maximal.

The λm value depends on the body temperature. The lower the temperature, the larger the λm value.

	c(1)	с(1) 0,29 10 2 mK
m	T
		13

Practical application of the 1 Wien’s law?

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•Much of a person's energy is radiated away in the form of infrared light. Some materials are transparent in the infrared, while opaque to visible light, as is the plastic bag in this infrared image (bottom). Other materials are transparent to visible light, while opaque or reflective in the infrared, noticeable by darkness of the man's glasses.

http://en.wikipedia.org/wiki/Black_body

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Temperatures of flames by appearance

The temperature of flames with carbon particles emitting light can be assessed by their color:

•Red

–Just visible: 525 °C (980 °F)

–Dull: 700 °C (1,300 °F)

–Cherry, dull: 800 °C (1,500 °F)

–Cherry, full: 900 °C (1,700 °F)

–Cherry, clear: 1,000 °C (1,800 °F)

•Orange

–Deep: 1,100 °C (2,000 °F)

–Clear: 1,200 °C (2,200 °F)

• White

–Whitish: 1,300 °C (2,400 °F)

–Bright: 1,400 °C (2,600 °F)

–Dazzling: 1,500 °C (2,700 °F)

•

http://en.wikipedia.org/wiki/Fire#Typical_temperatures_of_fires_and_flames

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Some interesting results gained from the 1-st Wien’s law

Body	Tav, K	λm, μ	λ value
			(observed)
The Sun	6000	0,4738	0,47
The Earth	288	10	3 - 80
Venus	600?	4,8	3 - 10?
Mars	265?	11	6 – 100?

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The total flux and 2-nd Wien’s law

The total flux of Bb radiation includes energy of all wavelengths

emitted by the body.						5
				B	C1				d
		B ,T d				C2
B				0
					exp			1
	0					T

After integration		5,67 10	8	W	2	4	Stephan-Boltzman
	B T 4
					m K		constant

2-nd Wien’s law

	C(!!) 1,301 10 5 W 3
B m ,T C(!!)T 5			5
	m	K

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Grey body

Since in the nature there are no absolutely black bodies, we may call all of them grey bodies.

The grey body is a body the absorption capability of which is the same for every wavelength.

a a const

Radiation flux of any grey body can be presented as;

F aB

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Extinction and Bouguer’s law

Notion of extinction

The term extinction means weakening of the radiation energy as its flux passing through a body (or atmospheric layer).

			F	Extinction=absorption + diffusion
	dl			Bouguer’s law holds: the flux of radiation is
			dF	extinguished proportionally to its intensity (Fλ),
				density of the medium it passes through (ρ),
				and the passing distance (dl).
							dF F dl
is mass extinction index, its dimension is m					2	Kg

dF
				Kg
F		dl		dl m2
		Kg	m
Dimensionless
		m3

To make right hand part dimensionless

must be m2

Kg

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Extinction (Ex) is function of absorption (Ab) and diffusion (Df). However, Ab = Ab(λ), and Df = Df(λ). Hence, the value of extinction

index depends on λ too.

			k			Kg m2			1
Volume extinction index					(*)	m3		m
							Kg

dF k F dl
			k	dF
Adopting dl 1;				F

The volume extinction index is numerically equal to the relative value of the radiation flux extinction as the beam of rays passes through a unit distance.

As it follows from the formula (*), the value of the volume extinction index depends not only on the medium composition but also upon its density. Therefore, it can be applied in case of non-variable density.

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