Lab#3

Lab #3: Light and the Properties of Waves Objectives: ● Practice making careful measurements ● Describe the relation between two variables in terms of one or the other ● Understand the properties of a wave (wavelength and frequency) and how they relate to each other as well as the energy of a wave Name: Betsy A. Lab partner(s): Date:2.26.24 WARNING • This lab uses a ruler that is difficult to read, but has FIVE (5) spaces between major number marks rather than FOUR (4): • That means that each minor number mark is not 0.25, but 0.2! • To make this a bit easier (and because I really don’t want

to spend my time taking points off for little mistakes), here is a reference for what sort of numbers you should use for each mark: • Warning #2: please round your answers. If you get something like 0.998234, that’s approximately 1. If you get 0.33289 that’s basically .333 which is approximately 1/3. I picked the numbers of this lab carefully to make these kinds of rounding easy. Part 1: Set up the simulation For this lab we are going to use the following simulation: https://phet.colorado.edu/sims/html/wave-on-a-string/latest/wave-on- a-string_en.html • FIRST: Hit the Pause button. Then select “No End” in the upper right and “Oscillate” in the upper left. Then select the Slow Motion option • NEXT, drag the Damping slider to None and drag the Tension slider to High. (The behavior of a wave depends on the medium, or material, it moves through. This lab also works for waves on a string or rope, but we will think almost exclusively about waves of light traveling in space, where there is no medium, so neither Damping nor Tension matter.) • NOW, turn on the Rulers in the lower right. You can click and drag to move these around. • FINALLY, hit Play and observe. 1. (0.5 pt) The simulation begins with a Frequency of 1.5 Hz or hertz. What is the definition of this unit? is the unit of frequency in the International system of Units is defined as one cycle per second.

Part 2: Observe Adjust the frequency to 1.5 Hz and wait for the wave to settle. Turn off the timer and turn on the Reference Line . Click and drag to align this with the highest possible spot that the wave touches—to mark the place of the wave peaks . Then pause the simulation when at least two wave peaks are touching this red Reference Line . 12. (3 pts) Using the horizontal ruler, measure the distance between these two peaks that touch the Reference Line You want to measure the distance from one peak to another, so measure between dots at the same position in the wave. Several may look like they are touching the reference line. Do your best; you only need a two digit number like 0.1 or 2.2. Wavelength of the 1.5 Hz wave with units 0.6667 13. (3 pts) Now set the frequency to 3.0 Hz and Wait at least 15 seconds, until the wave has adjusted to this new frequency. Then, measure the wavelength of the 3.0 Hz wave with units 0.3333 14. (2 pts) How much more is Q13’s frequency than Q12’s frequency? 0.5 Hz 15. (1 pt) Divide your answer for Q13 by your answer for Q12 : 2.003 16. (3 pts) Using your answers from Q14 and Q15, describe what happened to the wavelength when the frequency changed: The frequency _increases and decreases per second and the wavelength keep decreases as a result . Part 3: Think About It/Experiment further 17. (1 pts) When one wave (wave A) has twice (2x) the wavelength of another wave (wave B), what is the relationship between their frequencies? The frequency of wave A is 0.2234 the frequency of wave B 18. (2pts) When the frequency of a wave is tripled (3x), what precisely happens to the wavelength? When the frequency of a wave is tripled, the wavelength becomes one-third of its original value. 19. (4 pts) Light is an electromagnetic wave—a wave of electric and magnetic fields. The wavelength of red light is approximately 7 x 10-7 meters. The wavelength of blue light is approximately 4 x 10-7 m. If the energy of a wave increases with increasing frequency , which color of light has more energy—red, or blue? Blue light has more energy. 20. (1 point) What effect does the wavelength of a wave have on its amplitude? What about the frequency of a wave? The wavelength of a wave does not affect its amplitude. Similarly, the frequency of a wave also does not affect its amplitude

21. (3 pts, 0.25 each): The electromagnetic spectrum is a way to describe all of light, not just the very small bit of visible light that our human eyes have adapted to see. The graphic below represents the electromagnetic spectrum. Given what you know about visible light’s wavelength, frequency, and energy (see question 20), add the following labels to the appropriate sides of this diagram: higher and lower frequency ; longer and shorter wavelength ; higher and lower energy