Scientist Name: Student #: Date: LAB: Wave Basics, Interference, and Media-Transfer

Transcription

1 Scientist Name: Student #: Date: LAB: Wave Basics, Interference, and Media-Transfer Directive: READ and HIGHLIGHT THESE SAFETY TIPS FIRST I. Respect for Each Other a. When measuring with a meter stick, carry it by your side, not over your shoulder. b. Keep slinky and spring away from your neck. II. Respect for the Equipment a. Slinky i. ALWAYS HAVE YOUR EYES ON THE SLINKY. ii. When carrying slinky, use both hands on each opposite side of the slinky. Do not walk around with the slinky unless it is compressed all the way. Do not only use 1 hand. iii. If you are unsure of how to use the slinky as the lab instructs, ask your teacher. If you use the slinky incorrectly, you can create a kink in it, or tangle it, which may be difficult or impossible to remove, destroying the slinky. b. Spring i. When carrying the spring, use both hands and be sure that it is not dragging behind you for someone to trip over. Directive: STOP and wait for your teacher/class. You will be using a Frayer Model to Diagram the word: Medium

2 INTRODUCTORY READING: Directive: STOP. Wait for your teacher. 1. Then, Get the GIST. Read the first paragraph and orally summarize contents with a partner in twenty words or less. Does not need to be in complete sentences. 2. Read the second paragraph and orally summarize the first two paragraphs in twenty words or less. Waves are transmissions of energy but not matter, and they occur all over the natural world. Some examples of wave phenomena are: light, sound, water ripples. There are two main types of waves that are found in the physical world: transverse waves, and longitudinal waves (you will create these in lab). Wave phenomena abide by the same rules regardless of the medium (a material or empty space through which signals, waves, or forces pass) it is transferred through or in other words, there are not separate characteristics for light waves, or sound waves, or water ripples. Because of this we can investigate the characteristics of all waves using a coiled spring (slinky). Paragraph 1: Paragraph 1 +2: Summarize both paragraphs orally in ½ your words or less: PART 1: TYPES OF WAVES Directive: Get your slinky out of its box and stretch it between two people on the table. Circles are where teammates should sit. Definition: LONGITUDINAL WAVE: also known as a compression wave a longitudinal wave is a wave in which the vibrational displacement occurs in the same direction (parallel) as the motion of the wave. Directive: Create a longitudinal wave pulse by creating a disturbance in a direction parallel to the direction of the wave motion. Describe: What happens to the medium (slinky coils) as the pulse travels from one end to the other. Use the words: coils, energy, material, and medium in your answer. Definition: TRANSVERSE WAVE: a transverse wave is a wave in which the vibrational displacement occurs in a direction perpendicular to the motion of a wave. Directive: Generate a transverse wave pulse by moving your hand quickly to either the left or the right and then returning your hand to where it started. Describe: The motion of the medium as the pulse moves through it. Directive: Fill in the blanks with information you have learned so far.

3 PULSE: a disturbance in a that moves along in a wave. PARALLEL: when the motion of vibrational displacement occurs in the direction as the motion of the wave. PERPENDICULAR: when the motion of vibration displacement occurs at an angle of degrees with respect to the motion of the. WAVELENGTH: the length of a single. PART II: WAVE CHARACTERISTICS Directive: Use a cell phone stopwatch. Stretch the slinky out to 4-5 meters out on the floor for the questions. IF YOU NEED TO LET GO OF THE SLINKY, guide it back together with your hand SLOWLY. Be sure not to tangle the slinky in any other way. 1. Record the time it takes a short wavelength pulse to get to from one end to another, and return (a total of 8-10m traveled). Repeat this several times, changing the width from center (amplitude) of the pulse each time and recording the time from one end of the slinky to the other. Round results to 1 sig fig. Small Amplitude Medium Amplitude Large Amplitude Diagram: Diagram: Diagram: Time 1: Time 2: Time 3: Average time: Time 1: Time 2: Time 3: Average time: Time 1: Time 2: Time 3: Average time: How does changing the amplitude of the pulse affect how long it takes to get from one end to the other? 2. How long was your slinky stretched? meters. We can find the wave speed by using our speed equation. speed = distance. Find the average speed of each wave above (use the average time). time Small Amplitude Medium Amplitude Large Amplitude Work: Work: Work: Average Speed: m s Average Speed: m s Average Speed: m s

4 Directive: Fill in the following Frayer Model Diagram on the word: AMPLITUDE. Check out your partner s Frayer Diagram when they are done. My response and my partner s response are similar because: My response and my partner s response are different because: Now make any changes to make your Frayer Diagram as complete as possible! How much energy did a low amplitude pulse take for you to make? How much energy did a higher amplitude pulse take for you to make? A loud sound is a sound with high amplitude. Use the words: energy, amplitude, and wave to explain that sentence in terms of energy.

5 FREQUENCY: Directive: Summarize the 1 st paragraph in 20 words (not complete sentences) or less. Then summarize the 1 st and 2 nd paragraph in 20 words or less. Then all 3 in 20 words. Suppose that a hand holding the first coil of a slinky is moved back-and-forth two complete cycles in one second. The rate of the hand's motion would be 2 cycles/second. The first coil, being attached to the hand, in turn would vibrate at a rate of 2 cycles/second. The second coil, being attached to the first coil, would vibrate at a rate of 2 cycles/second. The third coil, being attached to the second coil, would vibrate at a rate of 2 cycles/second. In fact, every coil of the slinky would vibrate at this rate of 2 cycles/second. This rate of 2 cycles/second is referred to as the frequency of the wave. The frequency of a wave refers to how often the particles of the medium vibrate when a wave passes through the medium. Frequency is a part of our common, everyday language. For example, it is not uncommon to hear a question like "How frequently do you go to the grocery store?" Of course the question is an inquiry about how often you go to the grocery store and the answer is usually given in the form of "1 time per week." In mathematical terms, the frequency is the number of complete vibrational cycles of a medium per a given amount of time. Given this definition, it is reasonable that the quantity frequency would have units of cycles/second, waves/second, vibrations/second, or something/second. Another unit for frequency is the Hertz (abbreviated Hz) where 1 Hz is equivalent to 1 cycle/second. If a coil of slinky makes 2 vibrational cycles in one second, then the frequency is 2 Hz. If a coil of slinky makes 3 vibrational cycles in one second, then the frequency is 3 Hz. And if a coil makes 8 vibrational cycles in 4 seconds, then the frequency is 2 Hz (8 cycles/4 s = 2 cycles/s). Paragraph 1: Paragraph 1+2: Paragraph 1+2+3: Summarize both paragraphs orally in 20 words or less: 3. Stretch the slinky back to the length you had before. Now try generating more than one pulse. Slowly move you hand side to side at a constant rate. Diagram: Amplitude and wavelength with exactly how many waves you see on your slinky: Describe: What you see about the speed of the wave. (small, mid-size, large) Speed: Frequency: Wavelength: 4. Now move your hand side to side at a faster rate and describe what you see. Diagram: Amplitude and wavelength with exactly how many waves you see on your slinky: Fill in what happens to the speed, frequency and wavelength. (increase, decrease, stay the same) Speed: Frequency: Wavelength: 5. Now change the tension in the slinky. One person will gather about a quarter of the slinky in your hands making this the end and then stretch the remaining slinky 4 to 5 meters like before. Make a wave pulse with as close to an identical disturbance as you did above and record the time it takes travel away and back (8-10m). Repeat this again making the slinky even tighter. Describe how this changing the tension affects the characteristics of the wave (wavelength and speed). Tighter: Tighter Again: Time Wave Speed Describe:

6 III. Mathematical Relationship Between Speed, Frequency, and Wavelength Directive: Stretch the slinky as normal back out to 4-5 meters. Remember how amplitude didn t affect the speed of the wave? Go back and make sure you have that information in your Amplitude Frayer Diagram. Now move the slinky back and forth on one side. Have someone timing and someone counting how many times the slinky ONE HALF WAVELENGTH has been moved back and forth. Do this until you can get a certain number of standing waves (waves that look like they aren t moving backwards or ONE FULL WAVELENGTH forwards). When recording number of standing waves, be mindful of the following. Number of Standing Waves Times Moving the Slinky Back and Forth Total Time Keeping the Standing Wave Frequency of the Wave (f): f = # of back and forth motions Total time Measured Wavelength: length of slinky λ = number of standing waves Calculated Velocity of Wave (v): v = λf List the steps you had to take in order to find the wave speed for a standing wave IV. Wave Math Practice Directive: Using what you know about the velocity of objects, answer the questions to your best ability, including Knowns, Find, Drawing, Equation, and Solve. Box in your answers. 1. A slinky wave travels forward 5 meters in 2 seconds. Determine the velocity of the wave on the slinky. 2. You splash into an undisturbed pool and send waves around you in all directions. The distance between you and the nearest wall of the pool is 4m. A friend above water tells you it took about 8 seconds for the wave to hit the wall of the pool. What is the wave speed in the water? 3. You see a powerful lightning bolt strike a great distance away. Knowing that sound waves travel about 320 m through air, you count that it took 6 seconds before you heard the thunder (sound wave). How far s away did the lightning strike?

7 (# of cycles) f = t Directive: In your notebook, write down knowns, diagram the wave as best as you can, and solve. 4. Find the frequency when a slinky is moved back and forth 100 times in 10 seconds. 5. Find the frequency when 10 water waves hit the shore in 40 seconds. 6. Find how many times a slinky moves back and forth in 1 minute if it has a frequency of 1 Hz. (Hz means per second ( 1 ) and is the unit for frequency, GO BACK and edit answers for 1 and 2) s 7. Find how many wave hit the shore in 1 second if water waves hit the shore with a frequency of 0.5 Hz. 8. A sound wave travels at about 320 m at room temperature. If the frequency is 262 Hz (middle C for all s you musicians), find the wavelength of the sound wave. v = fλ Directive: Answer all questions in your notebook, the first 2 give you numbers to work with, as on the end of your lab manual. 9. What is the velocity of a wave with a frequency of 760 Hz and a wavelength of 0.45m? 10. What is the frequency of a sound wave moving at 340 m with a wavelength of 2m? s Directive: Prove these problems by putting your own numbers in. This is a useful way of answering conceptual problems. 11. What would happen to the velocity of a wave if the frequency is increased and the wavelength remains the same? 12. What would happen to the velocity of a wave if the frequency is doubled and the wavelength is cut in half? 13. What would happen to the wavelength of a wave as the velocity is increased and the frequency remains the same? 14. What would happen to the wavelength of a wave if the velocity is doubled and the frequency is doubled? 15. What would happen to the frequency of a wave if the wavelength is tripled and the velocity stays the same? 16. Green light has a wavelength of 5.20x10 7 m. The speed of light is 3 x 10 8 m. Calculate the frequency s of green light waves with this wavelength. 17. Blue light has a wavelength of 6.50x10 7 m. Use the speed of light to find the frequency. 18. Which light carries more energy, blue or green? Why? Connect your reasoning to the slinky lab!

8 V. Wave Interference Directive: Practice sending waves from opposite ends of the slinky at the same time. Label them as crest and trough. Directive: Send two transverse waves like the image shown: First: (one of very large amplitude, one small) Then: (both waves same amplitude and wavelength) Describe: what happens when the two waves meet. This is called destructive interference. Why do you think it is named this way? Directive: Practice sending waves from opposite ends of the slinky at the same time. Label them as crest and trough. Directive: Send two transverse waves like the image shown: First: (one of very large amplitude, one small) Then: (both waves same amplitude and wavelength) Describe: what happens when the two waves meet. This is called constructive interference. Why do you think it is named this way? These types of waves apply all over the universe. If two sound waves meet and interfere destructively, what do you think you would hear during the interference? Circle One: If two sound waves interfere constructively, you would hear a (louder) (quieter) (no) sound. Complete: the Venn Diagram. You must fill in 1 observation/idea per line (fewer allowed in the middle area). Destructive Interference: Constructive Interference:

9 VI. Waves Changing Media Directive: Look to see if a group is not using one of the two long springs, if there is one available, take it and attach it by winding one loose end of the slinky through the loop on one side of the spring. Do this so that 4 coils are in the loop of the spring. Directive: Stretch the slinky out to about 3 meters and let the spring lay loosely (but in line with the slinky) on the floor. Directive: Send a high amplitude and short wavelength transverse wave pulse down the slinky. Draw: both media (the slinky and spring) while the wave is: Only on slinky: While changing media: Done changing media: Describe: what happens when the wave encounters the different medium. When a wave hits something and then part (or all) of the wave moves backwards, this is called a reflection. Use the words: energy, wave, slinky, continue, reflect and spring to rewrite your description. Directive: Now have a teammate hold the slinky stretched out. Read, write, and then act. Read: have another teammate send 1 high amplitude and short wavelength transverse pulse from the relaxed spring. First, predict what you think will happen. Write: Prediction: Act: Try it! Draw: both media (the slinky and spring) while the wave is: Only on spring: While changing media: Done changing media:

10 Directive: Use your observations and pictures to fill in the following with words from the bank. You may repeat words. Smaller Larger Reflected Continued Large Small Mass When we sent a wave down the spring, a wave moved down the spring. When it encountered the slinky, a wave to the slinky, and a wave back onto the spring. This is because the spring has ( more / less ). Use the words: energy, wave, slinky, continue, change and spring to add information to the above sentences. A single sound wave pulse travels through the air and encounters a wall. Using what you have learned about waves changing media, describe what will happen in the most detail you possibly can, and draw a picture of a pulse traveling from air into a wall! Only in air: While changing media: Done changing media: Wall Wall Wall Think like a physicist: How would 1 wave pulse act after they pass through the wall and get to the other side? 1. Pulse only in air on side 1: 2. While changing from side 1 to wall: 3. Pulse in wall and reflected back into air on side 1 (S1): 1 Wall 2 1 Wall 2 1 Wall 2 4. Pulse changing from wall to air on side 2 (what happened to wave on S1?): 5. Pulse in air on Side 2 and reflecting back into wall: 6. Pulse meeting air on side 1 and will then back into the wall Wall Wall Wall