Information about Quantum Theory

simple intro to quantum theory, includes Bohr, deBroglie, emission spectrum, photoelectric effect

Waves: basic math C= speed of light distance / time = 3.0 x 10 8 m/s = wavelength or distance /wave That wavelength can be expressed in any unit, but to work with c, it must be in meters! V = frequency or Hertz, or waves/sec or just sec-1. In physics, they use f instead. (This is another way to write 1/sec)

C= speed of light

distance / time = 3.0 x 10 8 m/s

= wavelength or distance /wave

That wavelength can be expressed in any unit, but to work with c, it must be in meters!

V = frequency or Hertz, or waves/sec or just sec-1. In physics, they use f instead.

(This is another way to write 1/sec)

Overview So c= v tells us that Distance = distance x waves Second wave second c = x v OR Speed = distance/time

So c= v tells us that

Distance = distance x waves Second wave second

c = x v

OR

Speed = distance/time

Max Planck Studied the radiation of hot objects Continuous versus discrete energy Analogy: digital versus analog? If packets of energy are discrete, there must be some minimum size for one of these packets. That packet is called a quantum.

Studied the radiation of hot objects

Continuous versus discrete energy

Analogy: digital versus analog?

If packets of energy are discrete, there must be some minimum size for one of these packets. That packet is called a quantum.

Quantum Leap, and other dumb misuses of the term in pop culture... If a quantum is the smallest possible size for a packet of energy, it must be small, right? So why is a “Quantum Leap” huge? The term “Quantum physics” or “quantum mechanics” refers to the mathematical consequences of a quantized view of energy, and the specific math of the intensely tiny insides of atoms. The regular laws of physics don’t work very well on this tiny scale. We will discuss why, but will not take on the killer math. (you’re welcome!)

If a quantum is the smallest possible size for a packet of energy, it must be small, right? So why is a “Quantum Leap” huge?

The term “Quantum physics” or “quantum mechanics” refers to the mathematical consequences of a quantized view of energy, and the specific math of the intensely tiny insides of atoms.

The regular laws of physics don’t work very well on this tiny scale. We will discuss why, but will not take on the killer math. (you’re welcome!)

Richard Feynman, 1965 Nobel Laureate in Physics, for work in quantum electrodynamics “ I think I can safely say that nobody understands quantum mechanics.”

“ I think I can safely say that nobody understands quantum mechanics.”

How do you find the energy of a quantum? E = hv Where E = energy of a quantum in joules h = Planck’s constant or 6.626 x 10 -34 Js v = frequency in Hertz or sec-1 Quantum Leap by Cheryl Lavender

E = hv

Where E = energy of a quantum in joules

h = Planck’s constant or 6.626 x 10 -34 Js

v = frequency in Hertz or sec-1

Try a few of these problems What is the wavelength of light with a frequency of 8 x 10 14 Hz? What color is that light? What is the frequency of red light? What is the energy of a quantum of green light? What color light has a quantum size of 4.97 x 10 -19 joules?

What is the wavelength of light with a frequency of 8 x 10 14 Hz?

What color is that light?

What is the frequency of red light?

What is the energy of a quantum of green light?

What color light has a quantum size of 4.97 x 10 -19 joules?

The Photoelectric Effect Blue light shines on metal, electrons come off. Even a little blue light will do this. Red light shines on metal, nothing happens. Line up a dozen red lights, still nothing. This undermines the wavelength theory. Why?

Blue light shines on metal, electrons come off. Even a little blue light will do this.

Red light shines on metal, nothing happens. Line up a dozen red lights, still nothing.

This undermines the wavelength theory. Why?

Why is Einstein in this chapter? Einstein was obsessed with light. He recognized that Planck’s discrete packets of energy could explain the photoelectric effect. Einstein called the quanta of light PHOTONS Before Einstein, only the wave nature of light was recognized.

Einstein was obsessed with light. He recognized that Planck’s discrete packets of energy could explain the photoelectric effect.

Einstein called the quanta of light PHOTONS

Before Einstein, only the wave nature of light was recognized.

The Bubblegum machine analogy If this machine only accepts dimes, then feeding a hundred nickels into it won’t get you a gumball. You need the right amount of energy in one KICK to get an electron loose!

If this machine only accepts dimes, then feeding a hundred nickels into it won’t get you a gumball.

You need the right amount of energy in one KICK to get an electron loose!

Emission Spectra

Demonstration Materials: Spectroscopes, exciter, gas tubes Compare sunlight through spectroscope with “naked eye” light Compare fluorescent light through spectroscope with sunlight through spectroscope Observe hydrogen gas tube with spectroscopes How does sunlight differ from hydrogen’s emission spectrum?

Materials: Spectroscopes, exciter, gas tubes

Compare sunlight through spectroscope with “naked eye” light

Compare fluorescent light through spectroscope with sunlight through spectroscope

Observe hydrogen gas tube with spectroscopes

How does sunlight differ from hydrogen’s emission spectrum?

Why do we see lines and not a smooth rainbow?

Niels Bohr: a little bit right!

Bohr’s explanation of hydrogen’s spectrum Electrons exist at certain distances from the nucleus. Excited electrons absorb energy to jump further from the nucleus. When electrons fall back closer to the nucleus, they give off energy equal to that which they absorbed going up. E=hv, so the color tells us the energy!

Electrons exist at certain distances from the nucleus.

Excited electrons absorb energy to jump further from the nucleus.

When electrons fall back closer to the nucleus, they give off energy equal to that which they absorbed going up.

E=hv, so the color tells us the energy!

The famous LADDER ANALOGY An electron can only exist at certain distances from the nucleus. Intermediate distances are like being between rungs of a ladder. They just don’t support electrons.

An electron can only exist at certain distances from the nucleus.

Intermediate distances are like being between rungs of a ladder. They just don’t support electrons.

Why isn’t Bohr the final word on the subject? Atoms other than hydrogen have more than one electron. Their spectra are more complicated. Some atoms have electrons whose ground state isn’t the first possible energy level. The chemical behavior of atoms didn’t substantiate this view completely

Atoms other than hydrogen have more than one electron. Their spectra are more complicated.

Some atoms have electrons whose ground state isn’t the first possible energy level.

The chemical behavior of atoms didn’t substantiate this view completely

Louis de Broglie Considered Bohr’s “quantized orbits” Concluded that electrons must have a wave nature. Note standing wave patterns only exist when is a whole number ratio with the medium

Considered Bohr’s “quantized orbits”

Concluded that electrons must have a wave nature.

Note standing wave patterns only exist when is a whole number ratio with the medium

Now where do we stand? Light has a particle nature. Electrons have a wave nature.

Light has a particle nature.

Electrons have a wave nature.

But wait, there’s more! Werner Heisenberg: the Heisenberg Uncertainty Principle Erwin Schrödinger: Schrödinger’s wave equations

Werner Heisenberg: the Heisenberg Uncertainty Principle

Erwin Schrödinger: Schrödinger’s wave equations

The Dumb Heisenberg Joke... A cop stopped Heisenberg for speeding. Heisenberg rolled down the window. The cop asked him, “Do you know how fast you were going?” Heisenberg answered, “No, but I know where I am!”

A cop stopped Heisenberg for speeding. Heisenberg rolled down the window. The cop asked him, “Do you know how fast you were going?”

Heisenberg answered, “No, but I know where I am!”

Schrödinger’s wave equations We are not doing them! The math is too complex and not necessary. We will only consider the solutions without looking at the equations. The solutions, or quantum numbers, form a simple pattern. The equation above is just for describing hydrogen’s emission spectrum! Imagine how ugly it gets for bigger atoms!

We are not doing them! The math is too complex and not necessary.

We will only consider the solutions without looking at the equations. The solutions, or quantum numbers, form a simple pattern. The equation above is just for describing hydrogen’s emission spectrum! Imagine how ugly it gets for bigger atoms!

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