MEC203 - Quantum

Who discovered a simple mathematical relationship that described the effect of a change in temperature on the distribution of blackbody radiation?

Wien

Who first developed the concept of perfect absorber and emitter of radiation?

Kirchhoff

Who can rightly be considered the father of quantum mechanics?

Planck

What does Wien's displacement law state?

the wavelength at which the maximum amount of radiation is emitted multiplied by the temperature of a blackbody is always a constant. If the temperature doubles, the 'peak' wavelength will be half the previous length.

When was Wien's displacement law discovered

In February 1893

What were 3 crucial pieces of information that Planck had to construct his formula?

1. Wien's law (accounted for the intensity of radiation at short wavelengths)

2. Wien's law failed in infrared (where Rubens and Kurlbaum had found intensity was proportional to temperature)

3. Wien's law was correct

Explain how Planck's distribution law improved Wien's law to fit the experimental data at the time

It was more comprehensive because it fit all the experimental data not just the data from small wavelengths. Also, it was based on the second law of thermodynamics

Was Planck more impressed by Clausius's or by Kirchhoff's style of teaching?

Clausius's

(because his style of teaching was lucid and his clarity of reasoning enlightening)

Which physical law struck Planck 'like a revelation' when he was still a school boy?

The conservation of energy

When did Planck discover the equation for the distribution of radiation emitted by a blackbody? How old was he?

December 1900. He was 42

What did Isaac Newton show and when?

1666

a beam of white light is made up of different colours of light, he did this by passing it through a prism

What did William Herschel discover and when?

1800

infrared radiation by moving a mercury thermometer in front of a spectrum of light

What did Johann Ritter discover and when?

1801

ultraviolet radiation by observing silver nitrate darken when exposed to light

What did Kirchhoff develop?

The concept of a perfect absorber and perfect emitter of radiation - the blackbody

How did Kirchhoff envision the blackbody?

• simple hollow container w a tiny hole in one of its walls

• any radiation entering does so through the hole

• hole acts as perfect absorber

• radiation is reflected back and forth inside the box until fully absorbed

Why was progress halted and for how long?

• 40 years

• technical obstacles in constructing a blackbody and needing precision instruments

Describe Plank’s university career

• aged 16, october 1874 enrolled at munich

• moved to Berlin after 3 years, 1877

• was disappointed by Helmholtz and Kirchhoff’s dry teaching

• enthralled by Clausius

• returned to Munich after a year

• wrote a paper that flopped with his mentors

• 1880 became an unpaid lecturer (privatdozent)

• offered a professorship at Kiel in 1885

• asked to succeed Kirchhoff at Berlin as professor of theoretical physics in Nov 1888

• became senior physicist in 1894 after Helmholtz and Kundt died

What were the 2 laws of thermodynamics at the time?

1. conservation of energy

2. heat will not pass spontaneously from a colder body to a hotter one (entropy)

Who developed and defined theories on entropy?

Clausius

What did Planck do his doctoral thesis on? How was it received?

• concept of irreversibilty

• top physicists didn’t gaf

  • Helmholtz didn’t read it

  • Kirchhoff disagreed

  • Clausius didn’t even answer his letter

How did Planck become a professor?

He’s a nepo baby on his dad’s side