Phy 212: General Physics II 1/31/2008 Chapter 17 Worksheet: Waves II 1

Transcription

1 Phy : General Phyic /3/008 Chapter 7 orkheet: ae. Ethanol ha a denity o 659 kg/ 3. the peed o in ethanol i 6 /, what i it adiabatic bulk odulu? 9 N B = ρ = 8.90x0 ethanol ethanol. A phyic tudent eaure the length o a long, lender, copper rod. The Young' odulu o copper i.x0 N/ ; it denity i 8890 kg/ 3, the tie or the pule to trael ro one end to the other i.56 x 0 3. How long i the rod? Ycopper x Ycopper = = x = t = 5.49 ρ t ρ copper copper Sound: ntenity & Decibel 3. A blaring yte generate 50 o total power through a ingle pherical peaker. a. hat i the intenity o at a ditance o.0 ro the peaker? P 50 = = = πr 4 π() b. hat i the intenity o at a ditance o 0.0 ro the peaker? P 50 = = = πr 4 π(0 ) c. hat i the intenity leel, in decibel at a ditance o.0 ro the peaker? = 0dB log = 0 db - 0 β ( ) d. hat i the intenity leel, in decibel at a ditance o 0.0 ro the peaker? = 0dB log = 06 db - 0 β ( ) e. hat i the dierence in intenity leel in decibel at.0 and 0.0 ro the peaker? = 0dB log = 4 db β ( ). n general, what i the atheatical relationhip or the dierence in decibel leel between any ditance ro a ource? β β β = - = 0dB log - = 0dB log ( ) ( ) ( ) g. How would the intenity o (/ ) copare between a 00 yte and a 50 yte (copared at 0.0 ro the peaker)? = = 00 = 50 50

2 Phy : General Phyic /3/008 Chapter 7 orkheet: ae h. How uch louder in decibel would a 00 yte be at 0.0, copared to a 50 yte? β = 0dB log = 3 db 50 ( ) The intenity o a pherical wae at a ditance o 4.0 ro the ource i 0 /. hat i the intenity at a point 9.0 away ro the ource? P P 4 = = 0 and = 4 π(4) 4 π(9) 9 ( ) (4) (4) 0 (9) (9) 9 9 = = 9 = 0 = Application o Sound: Ultra aging 5. A deice utilizing ultra generate a wae with requency o 5.0x0 6 Hz. The deice end brie pule through the body tiue. Meaureent o the reultant echoe are ued to produce an iage (onogra) o a peron abdoen. The peed o in the body i 540 /. a. hat i the waelength o the ultraonic wae ued by thi deice? λ x0 Hz -4 = = = 3.08x0 6 b. Following a ingle pule, an echo i detected by the onitor 9.5 x 0-6 econd later. How deep in the tiue i the object/interace that produced the echo located? -6 t (540 /)(9.5 x 0 ) x = = = c. How uch tie would elape between echoe produced by the ront and back o an internal organ that i in thickne, a eaured ro the ront o the ultra tranducer? ( ) -5 x t = = = 3.90x0 540 d. Uing the peed o in huan tiue and auing that the tiue i eentially water, deterine the adiabatic bulk odulu in the body. 9 N body body 3 B = ρ = =.37x0 kg ( )( ) e. ould it be poible to obere an object o ize 0. uing thi ultra wae requency? not, what would be the iniu requency neceary to obere uch an object? No, the waelength o the ultra i 3.08x0-4. n order to reole an object, the waelength ut be aller than the object. Thereore, the iniu requency needed to iage a 0. object would be light greater than.54x0 7 Hz, probably ore like x0 7 Hz.

3 Phy : General Phyic /3/008 Chapter 7 orkheet: ae 3 The Doppler Eect (oing ource): 6. A wae ( =300 Hz) produced by a oing ource ( ource = 40 /) i obered by a tationary oberer. The peed o ( ) in abient air i 345 /. a. A the ource oe toward the oberer, how ar doe the ource trael between ubequent wae pule? One period ollowing the irt wae pule, the ource will eit a econd wae pule. Thereore, the ditance traeled by the ource will be: x = t = ( 40 ) = Hz ource b. hat i the apparent waelength o the wae a perceied by the oberer? 345 = - x = λ λ =.0 300Hz c. hat i the requency ( ) o perceied by the oberer? Note, when the ource i in otion, the peed o the wae reain the ae to both the oberer and the ource. λ ource - = = 339Hz or = = 339 Hz d. Doe the requency o the perceied wae increae or decreae when the ource i oing toward the oberer? hen the ource i oing away ro the oberer? increae a the ource approache the oberer & decreae a the ource oe away ro the oberer. e. hat i the atheatical relationhip between the requencie (actual) and (perceied) in ter o ource and when the ource i oing toward the oberer? = - ource. hat i the atheatical relationhip between the requencie (actual) and (perceied) in ter o ource and when the ource i oing away ro the oberer? = + ource

4 Phy : General Phyic /3/008 Chapter 7 orkheet: ae 4 The Doppler Eect (oing oberer): 7. A wae ( =350 Hz) produced by a tationary ource i obered by a oing oberer ( ource = 35 /). Aue the peed o ( ) in abient air i 345 /. a. hat i the waelength o the wae? 345 = λ = Hz b. According to the oberer, a he/he oe toward the ource, how at doe the wae appear to trael toward her/hi? = - = = + =380 ob ob c. hat i the apparent requency ( ) o the wae a perceied by the oberer? Note, when the oberer i in otion, the waelength o the reain the ae to both the oberer and the ource. 380 λ = = = 386Hz or = + ob = 386Hz d. hat i the atheatical relationhip between the requencie (actual) and (perceied) in ter o oberer and when the oberer i oing toward the ource? = + ob e. hat i the atheatical relationhip between the requencie, (actual) and (perceied) in ter o oberer and when the oberer i oing away ro the ource? = - ob. Doe the requency o the perceied wae increae or decreae when the oberer i oing toward the ource? hen the oberer i oing away ro the ource? increae a the oberer approache the ource & decreae a the oberer oe away ro the ource.

5 Phy : General Phyic /3/008 Chapter 7 orkheet: ae 5 Application o Doppler Eect: Radar Speed Detection 8. A police oicer ue a radar gun that generate a icrowae with requency o 36.0x0 9 Hz. The deice end brie icrowae pule toward obered oing ehicle. The radar gun then eaure the requency o incoing icrowae relected o the target ehicle and deterine the reultant Doppler requency hit ( ). Baed on the requency hit, the radar gun then calculate the oncoing peed o the ehicle. Note: the peed o a icrowae ( icrowae ) in air i 3.0x0 8 /. a. hat i the waelength o the icrowae wae ued by thi deice? 8 3.0x0 λ = = x0 Hz b. The tationary oicer target a car traeling directly toward hi and eaure a requency hit o 4000 Hz. How at i the car traeling? Note that changed ro 000Hz to 4000Hz Hz car= c = ( 3.0x0 ) = x0 Hz c. The poted peed liit i 30 ile/hr. the car exceeding the peed liit? i The car i peeding ince: ( ) hr hr = i d. Uually, thi particular oicer will not iue a peeding ticket unle the targeted car i traeling oer 5 ile/hr aboe the poted peed liit. Doe the oicer write thi ehicle a ticket? ye, the ehicle i traeling 7. ph oer the peed liit. e. hat would be the iniu requency hit that would need to be eaured to jut exceed the peed liit by 5 ile/hr? Note that changed ro 000Hz to 4000Hz. 9 ( )( ) car x0 Hz = = = 3754 Hz 8 c 3.0x0 ( ). The ae oicer target a car traeling at a 0 o angle with repect to the line o ight. A requency hit o 500Hz i recorded or the ehicle. How at i the car traeling toward the oicer? 8 ( 3.0x0 )( 500Hz) c eaured = = = 6.5 7x0 Hz 9 ( ) h. hat i the actual peed o the car? 6.5 car= = = 6.65 co0 co0 eaured o o car 0 o oicer