Notes

Slide Show

Outline

1	Background Introduction
2	Abstract/Introduction to the Presentation
3	The Nature of Light
4	What is Light? Light usually refers to visible light but can technically mean electromagnetic radiation of any wavelength
5	What is Electromagnetic Radiation?
6	How is EM Radiation categorized?
7	The answer is wavelengths!
8	How is EM Radiation categorized?
9	So what is the Nature of Light?
10	Some Wave Characteristics
11	Another Wave Characteristic
12	We will start with some Diffraction Demonstration Light diffracts when it enters a single aperture of comparable size to its wavelength
13	Diffraction Demonstration
14	Diffraction Demonstration
15	Another wave characteristic is interference. Let’s investigate Interference Patterns Just like sound waves interference but at a smaller scale A laser through double slits should look like:
16	Demonstration of Interference Patterns Interference of Double Slit
17	Demonstration of Interference Patterns
18	Nature of Light Now that we’ve seen some of lights characteristics as a wave, is there anything that suggests light acts like a particle too? To answer that question, we need to understand a particular phenomenon known as the photoelectric effect.
19	Photoelectric Effect The photoelectric effect is the process of emission of photoelectrons from a material after the absorption of energy from electromagnetic radiation
20	Photoelectric Effect The photoelectric effect is when a material emits photoelectrons after absorbing electromagnetic energy.
21	Solar Cells Solar cells convert electromagnetic energy (light) into electricity. It demonstrates the photoelectric effect because this electromagnetic radiation is absorbed by the material of a solar cell, emitting electrons. The emitted electrons are then driven by a voltage (potential difference) to produce a current (flow of electrons), and that is what electricity is.
22	Photoelectric Effect Applet But how does this demonstrate that light is a particle? Well, if light was strictly a wave, then increasing the intensity (brightness) of the light should increase the energy and number of electrons emitted However, only the number of electrons increases. The energy of the electrons do not increase. In a certain material like Sodium, an intense bright red light will be unable to emit any electrons, but a very dim blue light would be able to.
23	Photoelectric Effect Applet Einstein in 1905 explained this phenomenon by looking at light as packets of energy (photons). For example: The energy of Blue Light with wavelength about 400nm E = hf = hc/λ = 6.626x10^-34 J.S x 3 x 10^8m/s / 400 x 10^-9m Energy of Blue Light = 4.97 x 10^-19 Joules Energy of Red Light at 700nm = 2.84 x 10^-19 Joules
24	Photoelectric Effect Applet
25	Particle Wave Duality