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Lab 12 Wave Simulations AND Electromagnetic waves Learning objectives: 1) Explain how waves are generated, and whether they are motion of energy, particles, or both. 2) Classify waves based on the relationship between the velocity direction and medium vibration 3) Determine the relationships between frequency wavelength, period, and wave's velocity 4) Identify the units of frequency wavelength, period, and wave's velocity 5) Contrast amplitude and wavelength. 6) Solve problems that involve frequency wavelength, period, and wave's speed. 7) Determine the conversions needed to solve such problems 8) Explain the physical characteristics of electromagnetic waves. 9) State how electromagnetic waves of different frequencies are generated and detected. PART1: Wave Simulations: Read about longitudinal and transverse waves on the internet. A sample website is below http://hyperphysics phy-astr.gsu.edu/hbase/Sound/tralon.html Click on the following link and follow the instructions on how to use the simulations. http://www.physicsclassroom.com/Physics ... nd/Simple- Wave-Simulator/Simple-Wave-Simulator-Interactive you will need to switch between "rope and sound" 24.76 seconds போமாராக Pune We 0.38 ME 2.78. www 100 cm/ 277.8 cm de 2 cm E 100
Select dots to observe during the animation. Observe the movement of the dots with respect to the direction of the wave. Switch between "rope" and "sound". NOTE that the direction of both waves is from the left to the right of your screen. Answer the following questions: 1) In wave#1 (rope like) (a) Does the medium (dot) moved parallel or perpendicular to the wave? (b) What do we call this type of waves? (Transverse or longitudinal) 2) In wave#2 (slinky/sound like): (a) Does the medium (dots) move parallel or perpendicular to the wave? (b) What do we call this type of waves? (Transverse or longitudinal) 3) What do the waves represent? (motion of particles or energy transfer) Click on the following link http://phet.colorado.edu/en/simulation/wave-on-a-string Click on the simulation or download it. Check the "No End box on the top right, and check the "Ruler" box at the bottom right of the display screen (check the figure below) Ocm 9 10 Dar OO Figure (2) Place the cursor on the vertical ruler and line its zero with the beginning of the wave (as shown in the figure). Shake the string up and down, using the plier, to create waves as shown in the figure. Starts with small yanks and gradually vary how far you shift it up and down. observe the variation in the wave characteristics.
4) What would happen to the intensity (amplitude) of the wave when you increase the vertical displacement (shifting the plier further up and down)? (increase, decrease, stay the same) 5) What would happen to the intensity (amplitude) of the wave when the proximity from the source increases (when the wave moves further away from the source)? (increase, decrease, stay the same) Now, we need to alter the following: set the wave at Oscillate" instead of "manual" (using the window at top left corner of the screen) to generate continuous stream of waves ii. Check the box beside "Timer" so you could measure the time. iii. Set the wave at "Slow Motion instead of "Normal" to be able to observe the wave changes. Set the "Damping slider at "None" by shifting it all the way to the left. Set the Amplitude at 0.50 cm and the frequency at 1.00 Hz using either slider under them or the left/right arrows beside them. The display of the wave should be similar to figure 3. i. iv. V. Restart Ltd Oce Pule Ocm 2 3 8 0 cm 00.00.00 Amplitude 0.50 cm FRPG 100H Damong Tension Remem Figure (3) 6) With the frequency at the default (1.00 Hz). (a) Measure the wavelength 3" of the wave, in "cm", using the horizontal ruler. Note that you may control the ruler position using the mouse, and you may pause the wave's propagation at any
moment of time to do the measurements with ease. (b) Refer back to the notes or textbook for the definition of wave length and what it measures. 7) At 1.00 Hz frequency, count the number of waves you have in the figure. (a) How many waves does the 1.00 Hz generate? (b) Measure the time to complete one wave (period) using the timer. What is the period "Tin seconds? (c) Measure the velocity of the wave. Note: the v=fa" or "v= Fill in the blank: When the f= 1.00 Hz, =_ _cm, T- s, and v = 8) Increase the amplitude to 1.00 cm and measure the wavelength "*" again. (a) What is the wavelength 3" value (b) Did the wavelength 2" change? (c) Does the wavelength depend on the amplitude? (d) What is the period "T" in seconds? (e) Did the period T change? (c) Does the period "T depend on the amplitude? 9) Keep the amplitude at 1.00 cm. Increase the frequency to 2.00 Hz and measure the corresponding 1 and T, then calculate the speed of the wave (as you did in question (7). Fill in the blank: When the f= 2.00 Hz, 1 = s, and v= _cm, TE 10) What is the relation between the following: a) frequency and wavelength b) frequency and amplitude c) frequency and period d) wavelength and period e) velocity and frequency PART 2: Electromagnetic Waves Purpose After completing this experiment, you should be able to do the following: 1. Explain the physical characteristics of electromagnetic waves. 2. State how electromagnetic waves of different frequencies are generated and detected. 3. Calculate the frequency or wavelength of electromagnetic waves when the frequency or wavelength is given. 4. Give the relationship between frequency wavelength, and the speed of electromagnetic waves.
Equipment and Supplies A hand calculator is useful but not necessary. Discussion When a charged particle such as an electron, proton, or ion is accelerated, energy in the form of electromagnetic radiation emanates in all directions from the accelerated particle. An example of electromagnetic radiation is visible light, which consists of oscillating electric and magnetic fields that travel through vacuum at a speed of 3 x 108 m/s (186,000 mi/s). Your awareness of these printed words is due to the sensitivity of your eyes to electromagnetic radiation, which is reflected from the page of this lab-hand out. Electromagnetic radiation consists of oscillating electric and magnetic fields (vector quantities) perpendicular to each other and perpendicular to the direction of the wave motion. The fields are in phase. That is, their minimum and maximum values are at the same points in the oscillating cycle. Figure 9.1 illustrates the relationship between the force fields and the direction of the wave motion. Electrical vector Magnetic field vector Direction of propagation Electromagnetic waves consist of oscillating electric and magnetic fields. Note that the fields are at right angles to each other and also at right angles to the direction of the wave motion All electromagnetic radiation travels through empty space with a speed c. The speed, frequency fand the wavelength 2 (lambda) are related by the equation ca Eq. (9.1) where c. speed of the wave 3 x 10 m/s, f: frequency in hertz (Hz), 2: wavelength in meters (m) Very short wavelengths are often expressed in angstrom or nanometer units. One angstrom equals 10-10 m; one nanometer equals 10m. To convert angstroms to nanometers, move the decimal point one place to the left.
PROCEDURE 1 Electromagnetic radiation sensitive to the eye is called visible light and has frequencies ranging from 4.3 x 101 Hz to 7.5 x 10-4 Hz. Use Eq. 9.1 and calculate the wavelengths (in meters) for the frequencies given in Data Table 9.1. Record your answers in the lab report sheets. Use the conversion information given above and record the wavelengths in angstrom and nanometer units. Use Fig. 9.2 to obtain the color for the calculated wavelengths. Record the color for each wavelength in Data Table 9.1 The electromagnetic spectrum (an ordered arrangement of frequencies and/or wavelengths) is shown in Fig. 9.2. The spectrum is continuous; it ranges from low frequency radio waves to extremely high frequency gamma rays. There is no sharp dividing line between one type of wave and its neighbor. In fact, there is overlapping of frequencies, as shown in Fig. 9.2. Electromagnetic waves differ from one another only in their frequency or wavelength. Heat infrared Radio X-rays Gamma Ultraviolet Visible EHF SHF UHF VHF HF MF VLF 10-11 10-1 104 10- 10+ 10 10-4 10+ 10+ Wavelength in meters 4x100 5x1026x107x10 Wavelength im Figure 9.2 The electromagnetic spectrum. "E, extremely, F, frequency; H, high; L, low; M, medium; S, super, U, ultra; V, very. PROCEDURE 2 Plot a graph that shows the relationship between frequency and wavelength. Use the data in Data Table 9.1. Plot wavelength on the x axis. (You may use the graph template on Bb)
PROCEDURE 3 Table 9.2 lists the entire frequency range for each type of electromagnetic radiation. The values for the corresponding wavelengths are calculated using the equation c=fi. Note that the high frequency value in each range corresponds with the low wavelength value. Electromagnetic waves are generated and detected in different ways and by different devices, as listed in Table 9.2. Some of these may be unfamiliar to you. It is not feasible to give an explanation for all terms listed in columns one and two of Table 9.2. If you have a question concerning one or more terms, refer to an outside source. Project#2 will be a good opportunity to explore those sources. The next paragraph gives a brief explanation of how radio waves are generated by an LC circuit. They are also detected by the same type of circuit. An LC circuit consists of a capacitor C (two conductors separated by an insulator) and an inductor L (a conductor in the form of a coil). If the capacitor has an initial charge (stored electrons) and the switch S is closed (see Table 9.2, column two), the capacitor will begin to discharge. The total energy in the circuit, which is stored in the electric field between the two conductors, will be transferred by the flow of electrons to the magnetic field of the inductor. The magnetic field cannot sustain itself and collapses. This induces an electron flow in the circuit that places an opposite charge back on the capacitor. The process then repeats itself in the opposite direction. Thus electrons are accelerated back and forth between the capacitor and the inductor, and electromagnetic waves are generated. Because there is resistance (opposition to the flow of the electrons) in the circuit, energy must be continually supplied to the circuit, or else the oscillations will gradually die out.
Table 9.2 This table displays how Electromagnetic Radiations are generated and detected. Name of Radiation Radiation Generated by Accelerated electrons in an LC circuit Radio waves AM broadcast band FM broadcast band TV broadcast band Microwaves Radiation Frequency Wavelength Detected by Range Range Meters Hertz To be calculated (cycles/s) by student Approximate (meter) Values Electronic LC AM 0.55 x10° 187.5-545.5 circuit Charged- to 1.60 x10 coupled device FM 88 x10 to 2.7-3.14 (CCD) 108 x10 TV 54 x 10 to 0.34 - 5.56 890 x100 MW 1x 10 to 0.003 -0.30 1x 10" Infrared (heat waves) Visible light Ultraviolet Hot bodies Skin 1 x10" to 4.3 7.0x10^-0.003 (disturbed Thermometers x1094 molecules) Thermocouples Radiometers Hot bodies Eye 4.3x10 to 4.0x10 -7.0x10 (disturbed Photographic 7.5 x10 electrons in film atoms and Photocell molecules) Electric arcs Photographic 7.5x 10" to 3 x 1.0x10^-4,0x10 Special lamps film 10" (disturbed Photocell electrons in atoms) Special vacuum Photographic 3 x 10' to 3 x 1.0 x10"- 1.0 tubes film *10m (disturbed Geiger counter electrons in Ionization atoms chamber Radioactive Geiger counter Greater than 3 x Less than nuclei Ionization 1.0 x10m (disturbed chamber nucleus of Scintillation atoms) chamber X-rays 10 Gamma rays 10"
PROCEDURE 4 Electromagnetic radiation has a dual nature. Sometimes it acts as a wave; sometimes it acts as a bundle of energy. Max Planck, a German physicist, introduced the idea that a frequency generator could have only discrete or certain amounts of energy. The energy of the generator depends on its frequency according to the relationship E= hf Eq (9.2) where h (called Planck's constant) 6.67 x 10-34 J.s, f = frequency in Hz, and Era quantum of energy (called a photon) in joules This equations tells us that the Energy of the wave (its ability to penetrate material) is directly proportional to the frequency, and it does not depend on any other factors. NOTES
PART 2: Electromagnetic Waves Data Table 9.1 The Calculated Wavelengths for Visible Light Frequencies. Complete the table below. Use figure 9.2 to find the color (The first two rows were completed for you): Frequency f Wavelength Color (m) Wavelen gth 2 (Hz) 3.0x10 m/s 4.3 x 1014 7.0x10m Red 4.3x10* H: کی تر 5.0 x 104 6.0x10-- Yellowlorange 6.0 x 1014 7.5 x 1014 After applying procedure 2 and plotting the graph, answer the following: 1. State in words the relationship between frequency and wavelength that your graph illustrates. 2. (a) Give the name that describes the curve in your graph (parabola, straight-line, hyperbola) (b) What is the equation for the curve? QUESTIONS 1. What is the basic explanation for the origin of electromagnetic waves? (Read the discussion section)