__Ch. 27-29: Modern Physics__

__Ch. 27-29: Modern Physics__

__Reading__

Relativity - Ch. 27

Quantum - Ch. 28

Nuclear - Ch. 29

__Labs (depending on time available)__

Transistor lab

Semiconductor lab

Atomic Fusion weblab

__Homework__

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

Theory of Relativity_-_BJU_Ch._27_.pdf |

19._relativity_lecture_notes.docx |

20._quantum_physics_lecture_notes_2023.docx |

__Quantum 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. Since light moves at 3 x 10^8 m/s, 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 (for example from n=2 to n=1), it emits a photon having that much energy. Therefore, in order to jump up a level (say from n=2 to n=3), 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 the 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*represented by 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*(close to nucleus) might be -100 eV and

*n=3*(further from nucleus) 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.

__Transistor 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

15._transistor_lab_student_handout.pdf |

__Semiconductor lab__

- We have a fun semiconductor lab using a N555 timer chip. We'll do it if we have time.

__Flame Testing of Metals (Emission spectra lab)__

lab_handout__flame_testing_metal_ions_.pdf |

flame_test_chart_metal_ions.png |