Wednesday, Nov 17, 2010

Quiz on wave vocabulary and "Name that Sound"

Didn't get to do this today*********
Finish Bill Nye video
Go over and collect sheets for video
**************

Why do we make a big deal about transverse vs longitudinal waves?
They have different properties. Transverse waves can be polarized but longitudinal cannot.

Demo: picket fence and telephone cord

Demo: Polarizer on cell phone or calculator
Demo: seeing stress with polarized light. Use protractors to find stress points. Check out plastic fork. Now bend tine and check for different stress pattern.
Demo: polarization of corn syrup
Demo: milk powder in aquarium. See that transmitted light is reddish and scattered light is bluish. Check for polarization above and to the side.
Demo: Polarization of scattered light

Polarization is a property of just transverse waves like light.
Other properties are common to both transverse and longitudinal waves.

Sent a student out of the room and around the corner. Asked if they could hear me? see me? The sound waves bend around the corners so you can hear around corners. The light bends a little too, but it has a short wavelength so it does not bend as much.

Diffraction - the bending of a wave around a barrier or through an opening. The longer the wavelength, the greater the bending. Sound waves have a much longer wavelength than light so sound bends more. You can hear around corners but not see around corners due to diffraction.

Put a pencil in a cup of water. It appeared to be bent. This was due to refraction.
Refraction - the bending of a wave as it goes from one material into another.

Demo: marching line *****didn't do

Eyeglasses work by bending the light. Light takes the path of least time. Show how a converging lens can focus light.
Other examples: Einstein rings, mirages

Diversion into black hole discussion

Brought out a mirror - what do you see in it? A reflection. Light waves bounce off the surface of the mirror.

******Cut this short or didn't do: Held it up so one person could see the image of another. I then moved the mirror to the side and the first person could no longer see the image of the second. The angle of the incoming wave (incident wave) is equal to the angle of the outgoing (reflected) wave.******

We see because light is reflected off objects into our eyes. We, and the objects in the room are not hot enough to glow in visible light.

For some reason this didn't work well with Newton Computer screen*********
Showed belly-dancing tuning fork with computer. Waves are caused by vibrations. Waves are wiggles that move through space. If you look closely you can also see nodes and antinodes.*****************************

Collected RA 11.1
Handed out RA 11.2a, RA 11.2b and allowed students to get books and work on the reading assignments in class. Students didn't have time to work on homework in class

Microwaved CD and Soap.