Electromagnetic Radiation

Light is just one form of electromagnetic radiation. The relationship between the frequency of light and the wavelength is given by the equation:

c = ln

c = 3.00 X 10⁸ m/s = speed of light

l = wavelength

n = frequency

wavelength and frequency are ____________ proportional

The Photoelectric Effect

Einstein (1905)

(ROY G BIV)

Observations:

1. Light with a frequency less than that of red light shows ________________________________________

2. If the freq. is greater than or equal to that of red light, ____________________________________________

3. The kinetic energy of the ejected electrons _____________________________________

Einstein's Hypothesis:

Light has a dual nature:

Wave-Particle Nature of Light

Quotation: "Anyone who is not shocked by quantum theory has not understood

it."

-Niels Bohr

The Delayed Choice Experiment (Scientific American Jan. 1988, p. 46)

Experimental setup.

Procedure:

1. The laser is fired and one photon is sent into the beam splitter.

2. If the photon behaves like a __________ it will take either path A or A' as it leaves the beam splitter.

3. If the photon behaves like a _________ it will "split" in two and take both paths and interfere with itself.

4. After the photon leaves the beam splitter the switch is ______________.

5. If the switch is turned to the _____ position the photon either takes path A or path A' and is detected by the photodetector. It behaves as a _____________________

6. If the switch is turned to the _______ position the photon takes both paths and produces an interference pattern. It behaves as a _________.

How does the photon decide how to behave?

Possible Explanations

1. The photon knows how the switch will be turned in advance and makes a decision before leaving the beam splitter.

2. The nature of the photon is indeterminate until the switch is turned and an observation is made: the photon becomes a wave or becomes a particle.

3. God controls both the "decision" of the photon and the experimenter.

Atomic Emission Spectrum of Hydrogen

Continuous spectrum (electric arc; light bulb) vs. line spectrum (hydrogen lamp)

How can we explain the line spectrum of hydrogen?

The Bohr Model

Niels Bohr (1913)

Assumptions:

1. The electron in the hydrogen atom orbits around the nucleus with a ____________.

problem:_______________

2. The energy of the electron is ____________________________________-

Energy levels and the corresponding orbits in the Bohr model.

n = quantum no.:

3. Energy transitions

E₂ - E₁ = DE = hn = energy of the photon emitted

Problem: the Bohr model only works for H

Bohr model: