How are electromagnetic waves different from mechanical. waves? A Electromagnetic waves need a medium to travel through;

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1 B C B They re electromagnetic waves They re mechanical waves 1 What do seismic waves and sound waves have in common? It s carrying more energy The ground on to the next molecule in the chain? It becomes completely still A A Energy, but not matter Radio waves How is wavelength measured? It has a low amplitude It has a high frequency 10 Dt B direction of the energy flow? What type of waves carry energy at a right angle to the 7 mechanical waves don t mechanical waves can t mechanical waves aren t Name: r WAVES Date: Class: It returns to its original resting position B It has a high amplitude A continues It moving B vibrates rapidly from the buildup It of energy What can you infer about a wave with a short wavelength? 5 In a wave, what happens to a molecule after it passes energy D Neither energy nor matter What do waves carry from place to place? D Outer space A Theair B Energy and matter What medium do seismic waves travel through? C Its wavelength gets longer C Water C Matter, but not energy D P-waves A Compression waves C Sound waves C B ) Transverse waves D Seismic waves C Sound waves B It s moving through a denser medium A Water waves What does it mean when a wave s amplitude increases? D They re permanent waves C They re phonetic waves A Its frequency also increases Which of the following are electromagnetic waves? D Electromagnetic waves are long chains of vibrating molecules; () Electromagnetic waves can travel through empty space; waves can only travel through solid matter A Electromagnetic waves need a medium to travel through; waves? 6 How are electromagnetic waves different from mechanical BrainPOP, All rights reserved, visit us at D It has a ow frequency B Electromagnetic waves can travel through water; mechanical

2 definitions Lesson 4: Physics Waves Answer Key BrainPop Vocabulary Activity should be in students own words Frequency and Period of a Wave Check Your Understand mo Here is an example of a problem with a lot of extraneous information. The period is simply the reciprocal ot the frequency. in this case. the period is 1/(5 1.2 J-lz) which is seconds. O:Ofh/2 ciñf The quantity 121 times/second is the frequency. The period is the reciprocal of the frequency. T1/(121 liz) = s Frequency refers to the number of occultences of a periodic event per time and is measured in cycles/second. In this case. there are 10 cycles per 2 minutes (also known as 10 cycles per 120 seconds). So the frequenc is f=10 cycles / 120s = 4. Frequency refers to the number of occurrences of a periodic event per time and is measured in cycles/second. In this case. there is 1 cycle pei 60 seconds. So the frequency is f= 1 cycle / (60 s) (1 / 6 Hz Frequency refers to the number of occurrences of a periodic event per time and is measured in cycles/second. In this case. there is I cycle per 2 seconds. So the frequency is I cycles/2 s = 0.5 Hz. 6.( Period refers to the time for something to happen. In this case. the period is the time for one complete swine given as 2 seconds.

3 ... Don t Frequenc\ is the reciprocal ol the period. The period is 5 seconds, so the frequency is 1/(5 s) 0.20 Hz. 8. O.33 second Period refers to the time for something to happen and is measured in seconds/cycle, In this case. there are 11 seconds per 33 vibrational cycles. Ihus the period is (11 s) 7(33 cycles) 0.33 seconds. We now know that the period is 3.2 seconds and that the frequency is 0.31 Hz t/772 7 seo nd.s GIVEN:f 440 Hz FindT T = 1 / f= I / (440 HZ) = s 11. Period is the reciprocal of the frequency. So as f increases. I / I decreases. The Speed of a Wave Check Your Understanding 1. They reach the wall at th dme. Don t be fooled! The amplitude of a wave does not affect the speed at which the wave travels. Both Wave A and Wave B travel at the same speed. The speed of a wave is only altered by alterations in the properties of the medium through which it travels. 2. They reach the wall.. be fooled! The wavelength of a wave does not affect the speed at which the wave travels. Both Wave C and Wave D travel at the same speed. The speed of a wave is only altered by alterations in the properties of the medium through which it travels. GIVEN: v 340 m/s, d 20 m and f 1000 Hz Find time Lsevd tandrearrangetot=d;x Substitute nd solve.

4 4 The medium is the same for both of these waves ( the same container of nitrogen gas ). Thus. the speed of the wave will be the same. Alterations in a propert of a wave (such as wavelength) will not alyect the speed of the wave. Two different waves travel with the same speed when present in the same medium. 5. GIVEN: v = 340 m/s, t = s (down and back time) Find d (-wav) If it takes s to travel to the object and back, then it takes s to travel the one-way distance to the object. Now solve for time using the equation d = v t. d = v t = (340 mis) (0.075 s) = 6. The speed of a wave is unaffected by changes in the frequency. 7. GIVEN: d (i-way) =25 m, t (2-way)25 s Find v. lithe pooi is 25 meters long, then the back-and-forth distance is 50 meters. The wave covers this distance in 25 seconds. Now use v = d / t. v=d!t=(50m)/(25s) 8. If the wave travels 2.5 meters in one second then it will travel 5.0 meters in 2.0 seconds. If Wilbert gets drenched every time the wave has traveled 5.0 meters, then he will get drenched every 2.0 seconds.

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