# Origin of Quantum Theory

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29 Οκτ 2013 (πριν από 4 χρόνια και 8 μήνες)

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Origin of Quantum Theory

Photoelectric Effect

Compton Scattering

Origins of Quantum Theory

Who first postulated the idea of light quanta?

1. Planck

2. Bohr

3. De Broglie

4. Einstein

5. Heisenberg

Origins of Quantum Theory

Who first postulated the idea of light quanta?

1. Planck

2. Bohr

3. De Broglie

4. Einstein

5. Heisenberg

Origins of Quantum Theory

In the photoelectric effect experiment, current
flows when the light frequency is

1. less then the threshold frequency.

2. equal to the threshold frequency.

3. greater then the threshold frequency.

4. less than the cathode’s work function.

5. equal to the cathode’s work function.

Origins of Quantum Theory

In the photoelectric effect experiment, current
flows when the light frequency is

1. less then the threshold frequency.

2. equal to the threshold frequency.

3. greater then the threshold frequency.

4. less than the cathode’s work function.

5. equal to the cathode’s work function.

Origins of Quantum Theory

The minimum amount of energy needed to free an
electron from a piece of metal is called the

1. Gibb’s free energy.

2. quantum energy.

3. liberation potential.

4. threshold energy.

5. work function.

Origins of Quantum Theory

The minimum amount of energy needed to free an
electron from a piece of metal is called the

1. Gibb’s free energy.

2. quantum energy.

3. liberation potential.

4. threshold energy.

5. work function.

Origins of Quantum Theory

Planck

(1900)

E
n

= nhf

Photoelectric Effect

A. Einstein

(1905)

Bohr Atom

N. Bohr

(1911)

Compton scattering

Compton

(1923)

Origins of Quantum Theory

Hot Solid

Hot Gas

Cold Gas

Origins of Quantum Theory

Spectra

Emission or Line spectra

Absorption spectra

Origins of Quantum Theory

This is one way we identify interstellar elements.

Origins of Quantum Theory

What happens when you turn on the electric bunner on a stove?

Demonstration
-

light bulb filament

Demonstration
-

idea blackbody

Origins of Quantum Theory

How was the spectra measured?

Origins of Quantum Theory

Here is what they knew at the turn of the century.

The wavelength for maximum radiation is inversely
proportional to the temperature

The distribution of wavelengths depends

on the temperature only, not the material.

power

area

area under curve

Origins of Quantum Theory

T = ________

max = ________

max T = ________

T = ________

max = ________

max T = ________

T = ________

max = ________

max T = ________

What do you notice about these values?

6,000 K

5,000 K

7,000 K

425 nm

485 nm

3.0X10
-
3

mK

3.0X10
-
3

mK

3.0X10
-
3

mK

600 nm

They all have the same value.

Origins of Quantum Theory

Origins of Quantum Theory

Classical Theory (Maxwell’s Electromagnetic Theory)

Planck’s Theory (Quanta)

ultraviolet catastrophe

Origins of Quantum Theory

Photoelectric Effect

Origins of Quantum Theory

E
0

is the work function or binding energy

Origins of Quantum Theory

Origins of Quantum Theory

Origins of Quantum Theory

Origins of Quantum Theory

Origins of Quantum Theory

Origins of Quantum Theory

Origins of Quantum Theory

Origins of Quantum Theory

Origins of Quantum Theory

Origins of Quantum Theory

Origins of Quantum Theory

Origins of Quantum Theory

Origins of Quantum Theory

The work function of metal A is 3.0 eV. Metals B and C have
work functions of 4.0 eV and 5.0 eV, respectively. Ultraviolet
light shines on all three metals, creating photoelectrons. Rank
in order, from largest to smallest, the stopping voltages for A,
B, and C.

1.
V
A

>
V
B

>
V
C

2.
V
C

>
V
B

>
V
A

3.
V
A

=
V
B

=
V
C

Origins of Quantum Theory

The work function of metal A is 3.0 eV. Metals B and C have
work functions of 4.0 eV and 5.0 eV, respectively. Ultraviolet
light shines on all three metals, creating photoelectrons. Rank
in order, from largest to smallest, the stopping voltages for A,
B, and C.

1.
V
A

>
V
B

>
V
C

2.
V
C

>
V
B

>
V
A

3.
V
A

=
V
B

=
V
C

Origins of Quantum Theory

The intensity of a beam of light is increased but the light’s
frequency is unchanged. Which of the following is true?

1. The photons travel faster.

2. Each photon has more energy.

3. There are more photons per second.

4. The photons are larger.

Origins of Quantum Theory

The intensity of a beam of light is increased but the light’s
frequency is unchanged. Which of the following is true?

1. The photons travel faster.

2. Each photon has more energy.

3. There are more photons per second.

4. The photons are larger.

Origins of Quantum Theory

Compton Scattering

Origins of Quantum Theory

Compton Scattering

Origins of Quantum Theory

Classical Scattering of Electromagnetic Wave

So the radiation wavelength is the
same as the incident wavelength.

We do not have to consider the magnetic field
since it is so small compared to the electric field

Origins of Quantum Theory

Compton Scattering

Answer the first three questions in the tutorial and draw the
diagram for the scattering experiment.

Discuss the Compton experiment in your group. What are the
two physical quantities in the collision?

What is the assumption for light that Compton used?

That light behaved like a particle with energy

And momentum

Origins of Quantum Theory

Compton Scattering

What two equations (conservation law) did Compton use to
find the change in wavelength?

Draw the collision between the electron and the photon. Label
the angles

and

.

Conservation of energy

Conservation of momentum

Origins of Quantum Theory

Write the energy and momentum for each before and after the
collision

Conservation of Energy

Conservation of Momentum

Origins of Quantum Theory

Write the energy and momentum for each before and after the
collision

before

after

electron

photon

?

Origins of Quantum Theory

Origins of Quantum Theory

Solid

Hot Gas

Cold Gas

Origins of Quantum Theory

Planck’s Theory (Quanta)

Classical expression

Origins of Quantum Theory

Planck’s Theory (Quanta)

Origins of Quantum Theory

Optical Pyrometer

Origins of Quantum Theory

Microwave Cosmic Background

Origins of Quantum Theory

Origins of Quantum Theory

Use

the

results

above

and

substitute

into

the

conservation

equation
.

Do

the

same

for

conservation

of

momentum

in

the

x

direction
.

Now

for

momentum

in

the

y

direction
.

Compton

solved

these

three

equations

to

find


=

-

.

Where

is

the

initial

wavelength

for

the

photon

and

is

the

final

wavelength

for

the

photon
.

What is the final results (Compton’s equation) that Compton
found?