Reviewed reflection and refraction.
Asked what value students got for the index of refraction of light in water. Used this value to calculate the speed of light in water.
Showed again that when going from fast to slow the wave bends towards the normal. When going from slow to fast, the wave bends away from the normal.
In going from slow to fast, as you increase the angle of incidence, you reach a point where the angle of diffraction is 90 deg. If you increase the angle of incidence any more, you do not get a refracted ray, instead you get total internal reflection. Demonstrated total internal refraction with laser and optic fiber.
Defined and calculated the critical angle.
Other examples of refraction are mirages and the fact that the Sun is already really well below the horizon when you see it setting.
Talked about diffraction - bending or spreading of a wave as it passes through an opening or around a barrier. Sent student out into hallway. They can hear you but not see you. Calculated the wavelength of the sound wave and compared it to the wavelength of light. Longer wavelengths are diffracted more. That is why you can hear around corners but not see around corners.
Used circular pattern overheads to demonstrated diffraction and interference.
Young's double slit diffraction experiment was used to measure the wavelength of light. Described the set-up and math for the experiment.
We used a double slit to measure the wavelength of laser light.
I then showed how to measure the wavelength using a ruler. We got a value of 590 nm.
Handed out worksheet on reflection and refraction.
Thursday, February 26, 2009
Wednesday, Feb 25, 2009
Collected RA 18.1
Talked about reflection and refraction.
Reflection - for specular reflection, angle of incidence = angle of reflection. Defined the normal. Did problem of viewing self in mirror - how much mirror do you need. Demo of how much of you you can see vs how far away you are.
Mentioned diffuse reflection.
Refraction - Bending of a wave as it goes from one medium into another in which it travels at a different speed. Demo in hallway using people wave.
Sketched pictures of the demo on the board defining wave front and ray. Show that when going from fast to slow, the ray bends towards the normal.
Introduced Snell's Law - n1 * sin(theta1) = n2 * sin(theta2)
n is the index of refraction. For light n = c/v
For other waves, sin(theta1)/v1 = sin(theta2)/v2
Students did lab on measuring the speed of sound using the tube.
Lab write-up due Friday: Include Name, Partners, Date, Name of Lab
Brief description of lab, data table, measured speed of sound.
Calculate the the accepted value and compare measured to accepted for that temperature.
Students also did the Snell's Law lab in which they measured the index of refraction of water using the semi-circular containers. Students measured the angles of incidence and refraction and then used the laptops with Excel to make a data table and plot sin(angle of incidence)/sin (angle of refraction). The slope gave the index of refraction of water assuming the index of refraction in air is 1.
Write-up: Name, Partners, Date, Name of Lab
Brief description of lab, data table, graph from Excel, Conclusion.
Both lab write-ups are due on Friday
Talked about reflection and refraction.
Reflection - for specular reflection, angle of incidence = angle of reflection. Defined the normal. Did problem of viewing self in mirror - how much mirror do you need. Demo of how much of you you can see vs how far away you are.
Mentioned diffuse reflection.
Refraction - Bending of a wave as it goes from one medium into another in which it travels at a different speed. Demo in hallway using people wave.
Sketched pictures of the demo on the board defining wave front and ray. Show that when going from fast to slow, the ray bends towards the normal.
Introduced Snell's Law - n1 * sin(theta1) = n2 * sin(theta2)
n is the index of refraction. For light n = c/v
For other waves, sin(theta1)/v1 = sin(theta2)/v2
Students did lab on measuring the speed of sound using the tube.
Lab write-up due Friday: Include Name, Partners, Date, Name of Lab
Brief description of lab, data table, measured speed of sound.
Calculate the the accepted value and compare measured to accepted for that temperature.
Students also did the Snell's Law lab in which they measured the index of refraction of water using the semi-circular containers. Students measured the angles of incidence and refraction and then used the laptops with Excel to make a data table and plot sin(angle of incidence)/sin (angle of refraction). The slope gave the index of refraction of water assuming the index of refraction in air is 1.
Write-up: Name, Partners, Date, Name of Lab
Brief description of lab, data table, graph from Excel, Conclusion.
Both lab write-ups are due on Friday
Tuesday, Feb 24, 2009
Handed back and went over SHM test
Reviewed characteristics of waves.
Showed oscilloscope demo with frequency generator. Long wavelengths produce low pitch, low frequency sounds. Short wavelengths produce high frequency, high pitch sounds. Showed the same with the pull-a-tune. The longer bar produces a longer wavelength wave and a lower note.
Students did slinky lab in hallway and also used the Vernier equipment to measure the speed of sound in air using the singing rods.
Handed out RA 18.1 due tomorrow.
Reviewed characteristics of waves.
Showed oscilloscope demo with frequency generator. Long wavelengths produce low pitch, low frequency sounds. Short wavelengths produce high frequency, high pitch sounds. Showed the same with the pull-a-tune. The longer bar produces a longer wavelength wave and a lower note.
Students did slinky lab in hallway and also used the Vernier equipment to measure the speed of sound in air using the singing rods.
Handed out RA 18.1 due tomorrow.
Friday, Feb 20, 2009
Reviewed for SHM test. Answered any questions from worksheet. There weren't very many questions.
Started lecturing on waves.
Two types of waves - mechanical and electromagnetic
Waves can also be classified as longitudinal or transverse.
Used slinky to show features of each wave and also to show the relationship between frequency, energy, and wavelength.
Introduced the equation, v = f*wavelength
Found wavelengths of AM and FM radio waves. Wavelength of microwave is about 1 ft to fit inside the box in kitchen.
Test tomorrow on SHM
Started lecturing on waves.
Two types of waves - mechanical and electromagnetic
Waves can also be classified as longitudinal or transverse.
Used slinky to show features of each wave and also to show the relationship between frequency, energy, and wavelength.
Introduced the equation, v = f*wavelength
Found wavelengths of AM and FM radio waves. Wavelength of microwave is about 1 ft to fit inside the box in kitchen.
Test tomorrow on SHM
Wednesday, February 18, 2009
Wednesday, Feb 18, 2009 - Block 3
Class started slowly with several students out giving blood.
Handed back RA 11.1 and asked if there were any questions. I graded the RA part out of 10 and assigned a grade for the problem part. There were 5 answers so I graded it out of 5.
Reviewed and finished problem of block bobbing in water.
Drew sketches of x, v, and a for SHM and showed that the slope of the displacement gives the velocity and the slope of the velocity gives the acceleration.
Covered energy in SHM. Showed that the elastic PE is given by 1/2 k x^2.
E total = 1/2 k x^2 + 1/2 m v^2 = 1/2 k A^2 = 1/2 m vmax^2
Drew sketches of E vs x.
Students calculated the value of x for which KE = elastic PE.
Did problem of SHM with tunnel through the Earth. Showed that the period is 84 min so that you get from one side to the other in 42 min.
Finished class by describing the IB lab - What are the factors that affect the period of a pendulum.
The design part must be done individually and is due on Friday. After that, students may work with a partner for the data collection. I instructed the students to think about using the Vernier lab equipment for data collection. Students will have to design their own pendulums.
Asked students to continue working on the remainder of the problems on the SHM problem sheet.
Test early next week.
Spring constant lab due tomorrow.
Handed back RA 11.1 and asked if there were any questions. I graded the RA part out of 10 and assigned a grade for the problem part. There were 5 answers so I graded it out of 5.
Reviewed and finished problem of block bobbing in water.
Drew sketches of x, v, and a for SHM and showed that the slope of the displacement gives the velocity and the slope of the velocity gives the acceleration.
Covered energy in SHM. Showed that the elastic PE is given by 1/2 k x^2.
E total = 1/2 k x^2 + 1/2 m v^2 = 1/2 k A^2 = 1/2 m vmax^2
Drew sketches of E vs x.
Students calculated the value of x for which KE = elastic PE.
Did problem of SHM with tunnel through the Earth. Showed that the period is 84 min so that you get from one side to the other in 42 min.
Finished class by describing the IB lab - What are the factors that affect the period of a pendulum.
The design part must be done individually and is due on Friday. After that, students may work with a partner for the data collection. I instructed the students to think about using the Vernier lab equipment for data collection. Students will have to design their own pendulums.
Asked students to continue working on the remainder of the problems on the SHM problem sheet.
Test early next week.
Spring constant lab due tomorrow.
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