Physics 7C SS1, Lecture 10

Quiz 4

Quantum Mechanics

Evaluations

Agenda Any questions about electric potential

energy (PEelec), electric potential (V), their relationships to Felec and/or E?

Any questions about magnetism? Quiz 4 Final information Quantum Mechanics Evaluations

Quiz 4

Current flows into the page; asked about field and force at star’s location

Final Exam As comprehensive

as 1hr 15 minutes can be

Bring calculator, straight edge, ID

As comprehensive as 1hr 15 minutes can be Probably 5 questions (?)

Quantum Mechanics Light and matter both behave like waves

sometimes and like particles other times Confining waves to an area leads to standing

wave patterns For bound matter, this results in only certain

available energy levels Bound matter can gain or lose energy only

between the available levels To conserve energy, usually a photon is absorbed

or emitted with the correct energy (frequency)

Experimental Evidence: Photons

Electrons in metal: Free to move Bound to metal

Think of as binding energy Goal: free from metal

Shine light to add energy. How can we get high energy light?!

Laser

Metal

v

Energy: Photon Model Changing color of light:

If red light does not free electrons, sometimes other colors will

If purple light does not free electrons, no visible light will.

Color (frequency) of light is related to the energy! E = hf = energy of one photon h: Plank’s Constant = 6.62610-34Js

Increasing intensity corresponds to increasing number of photons.

Which type of EM radiation is highest energy?

b) Visible c) X-raya) Radio

Quantum Mechanics: Light

As a wave As a particle: E=hf

Matter As a wave: =h/p As a particle: as you have always studied!

Quantum Mechanics Consequences of wave nature of matter

2-slit interference occurs for particles Confining a particle leads to standing waves

Different standing waves have different wavelengths Different wavelengths correspond to different momenta Different momenta correspond to different energies

All these things are quantized: only certain values are allowed

Atoms: electrons bound to nucleus

Molecules: can model bonds as springs, with atoms bound together

Examples of bound particles

N N

Example of energy levels: Emission Spectra Add energy to an element and wait. Each element

emits light of certain colors. Why?

Hydrogen

Helium

Iron

Emission Spectra Each of the three marked transitions

correspond to visible light. Which one is responsible for the red photon?

E1

E2

E3

E4

E5

a b c

The three previous transitions corresponded to visible light. What part of the spectrum might the bold arrow correspond to?

a) Green light

b) Infrared (IR)

c) Ultraviolet

d) Microwave

e) Gamma ray

Emission Spectra

E1

E2

E3

E4E5

The End Questions?

You’re 1DL and 1 final exam away from completing physics. Congrats!

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