agenda1. Physics presentations2. What you should know about lightUpdates:- EXTRA CREDIT OPPORTUNITY: construct a mobile that is at least three levels - What physics concept does this involve?
Mobiles use torque!• Be creative – make the mobile reflect YOU and your interests, or have a theme to the mobile!• The more levels, the more extra credit
Physics in the summer olympics!• Order will be based on volunteer, and then based on names picked from popsicle sticks• YOU WILL LOSE POINTS if you interrupt another group’s presentation• There will be time for questions at the end• I will be timing your presentations
What you should know about light• How light supports the wave model of light: • It reflects, refracts, diffracts, and can be polarized.• Recognize that light has a finite speed• Know the order of visible light on the electromagnetic spectrum and how the color of light tells us about the wavelength, frequency, and energy contained in light.
Electromagnetic spectrum• Visible light is just a small portion of the EMS• We see that from ROY G. to BIV • Wavelength gets shorter • Frequency gets higher • Energy gets higher
Wave-particle duality theory• Light is a more complex phenomenon than just a simple wave or a simple beam of particles! Phenomenon Explained in terms of Explained in terms of waves? particles? Reflection ✔ ✔ Refraction ✔ ✔ Interference ✔ ✗ Diffraction ✔ ✗ Polarization ✔ ✗ Photoelectric Effect ✗ ✔
reflection• It allows us to see objects as different colors • All other colors are absorbed White Only red light light is reflected
Reflection & direction • The direction of light reflected depends on the direction that light is aimed at a reflective object NormalIncident ray Reflected ray Angle of Angle of incidence reflection Mirror
Using mirrors • Two examples: 2) A car headlight 1) A periscope
refraction• As light goes from one medium to another, the path of light bends • Velocity changes, so its path changes. • Analogy is a troop of soldiers going from firm ground to mud
refraction• As light goes from one medium to another, its path changes.• Some light is reflected, while some is refracted!
Refraction – Snell’s Law• A scientist by the name of Snell discovered that the ratios of the index’s and the ratio of the sine of the angles are the same value! • n = index of refraction • Index of refraction is a function of wavelength – the longer the wavelength, the less light will bend n1 sin θ 2 = n2 sin θ 1 Snell s Law n1 sin θ1 = n2 Sinθ 2
refraction• Index of refraction is also the ratio of the speed of light in a vacuum to the speed of light in that substancen=c v
diffraction• Bending of waves around the edge of a barrier. New waves are formed from the original.
Light interferences• Constructive & destructive interferences can cause light and dark patterns of light
dispersion• Each color has a different wavelength, so they bend differently when going into a new medium since index of refraction depends on the wavelength for that media. • It is greater for shorter wavelength – which color on the spectrum has the smallest wavelength?
Reflection & refraction allow us to see rainbows!• Sun rays are hit by spherical water droplets and are reflected off the back surface.• Red is bent the least (since it has the lowest wavelength) so it reaches the observer’s eye from higher in the sky!
Polarized waves P• The alignment of electromagnetic waves in such a way that the vibrations of the electric fields in each of the waves are parallel to each other. • Bottom line…polarizing light shields some light by block the light at right angles from the polarizer.
Facts about Light The speed of light, c, is constant in a vacuum. Light can be: •REFLECTED •ABSORBED •REFRACTEDLight is an electromagnetic wave in that it has wave like properties which can beinfluenced by electric and magnetic fields.