__Ch. 27-30: Modern Physics__ Relativity, Quantum and Nuclear Physics

__Ch. 27-30: Modern Physics__

__Reading__

Young & Geller book. Read the sections of Ch. 27-30 which are indicated below.

__Topics__

Relativity - Ch. 27. Read and study sections 27.1 through 27.5.

Quantum Physics - Ch. 28. Read and study sections 28.1 through 28.3.

Nuclear Reactions - Ch. 30. Read and study sections 30.1 through 30.7.

__Labs (depending on time available)__

Transistor Switching lab

Atomic Fusion PhET weblab

Flame Testing of metal salts for emission "line spectra"

__Homework__

I will assign selected end-of-chapter problems. See Canvas for instructions and due dates.

19._relativity_lecture_notes.docx |

20._quantum_physics_lecture_notes_2023.docx |

__Quantum Physics chapter summary__

A

*photon*is simply a packet of light (or other electromagnetic energy). The energy

*E*of a photon is given by

**where h is Planck's constant and**

*E=hf**f*is the frequency. Planck's constant is 6.6 x 10^-34 J-s, but also can be expressed in electron volts as 4.1 x 10^-15 eV-s. Therefore, you can say 1 eV = 1.6 x 10^-19 J. The frequency

*f*is in cycles/s, otherwise known as Hertz (Hz).

Velocity of a wave is

*frequency*x

*wavelength*

*. This is basic wave mechanics that we learned a long time ago. Furthermore, light moves at 3 x 10^8 m/s, so we can set*

**v = fλ***v = 3.0 x 10^8 m/s*when talking about electromagnetic waves.

Bohr said that you have energy levels within a hydrogen atom (n=1, n=2, n=3), and the single electron in the H atom can only occupy these discreet energy levels or 'orbitals'. The orbital closest to the nucleus is n=1, and the numbers get bigger as you go outward. When an electron jumps down a level (from example from n=2 to n=1), it emits a photon having that much energy. Therefore, in order to jump up a level (or two, or three levels), it must absorb a photon having sufficient energy. If the incoming photon doesn't have enough energy (i.e. high enough frequency), it won't elevate the electron to a higher level. Like I said above, the energy of a photon is given by

*E = hf*, and therefore the higher the frequency is, the more energy that photon will possess. The energy can be calculated in Joules (a really big unit of energy) or electron volts (a really small unit of energy). I gave you the conversion factor above, so you can convert between J and eV easily. Another thing: the total energy

*E*of each 'orbital' is stated as a negative number, just like you would expect: the closer an electron is to the nucleus, the larger the negative number becomes, because it's sitting in a larger 'energy hole'. So, for example,

*n=1*might be -100 eV and

*n=3*might be -11 eV.

The

__radius__of a given energy level

**(n=1, n=2, etc) within the Bohr atom is directly proportional to n^2. In other words,**

*n***. That means n=2 would have a radius 4 times larger than n=1, and n=3 would have a radius 9 times larger than n=1, and so on. ALSO, the total**

*radius ∝ n^2*__energy__of a given energy level

*n*is

*inversely proportional*to -

*n^*2. In other words,

**. So for example if**

*energy ∝ 1/-n^2**n=1*was -100 eV, then

*n=2*would be -25 eV, and

*n=3*would be -11 eV. If you kept going out from the nucleus, n(infinity) would have total energy = 0.

__Flame Testing of Metals (Emission spectra lab)__

lab_handout__flame_testing_metal_ions_.pdf |

flame_test_chart_metal_ions.png |

__Transistor Switching lab__

- We will explore how transistors work as switches and amplifiers, by making circuits using transistors
- We will measure the current gain (IE/IB) of the 2N2222 transistor, and discuss what that means

transistor_switching_lab_handout.pdf |