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General Physics ph 202 Name:____________

Midterm III (Ch 11 19) Type

!e"r#ary 2$% 200&

Exam is closed book and closed notes. Use only your note card.

'rite all r* and ansers in the clr papers pr+ided, Show all your work and explain your reasoning(No credit will be given for

an answer that does not include the necessary solution or explanation, exceptfor true/false or multiple choice uestions!

"artial credit may be awarded for a correct method of solution, even if the

answer is wrong.

Part I Tr#e r !alse (1,- pints each):#or uestions $ % $&, state whether each

statement is true or false.'. y test type is )))))))).

$. #alse * wave pulse on a string whose end is fixed is reflected without inversion.

&. #alse +ound waves in air are transverse waves.. -rue nfrasound carries over long distances better than ultrasound.

. #alse0ats use infrasound to navigate.

1. -rue * concave lens always produces a virtual image.2. #alse#or total internal reflection to take place, light must go from a medium of lower

index of refraction to a medium of higher index of refraction.

3. -rue * convex mirror always produces a virtual image smaller than the ob4ect.

5. #alseagnification is positive for inverted images.6. #alse-he index of refraction for a given material is directly proportional to the

freuency of light.

$'. #alse* convex lens is known as a diverging lens and a concave lens is known as a

converging lens. (reverse is true!$$. #alse-he reflection of light from a rough surface is called specular reflection.

$&. -ruen a concave mirror the inside of the spherical surface is the reflecting surface.

Part II M#ltiple Chice (1,- pints each): 7hoose the one correct answer for each of

the following uestions that best answers or completes the uestion.

$. -he velocity of propagation of a transverse wave on a &.'8m long string fixed at bothends is &'' m/s. 9hich one of the following is not a resonant freuency of this

string:

*! 1' ;< 0! &'' ;< 7! $'' ;< =! &1 ;

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$. 9hich of the following is a false statement:

*! +ound can travel through a vacuum.0! ?ight travels very much faster than sound.

7! +ound waves are longitudinal pressure waves.

=! -he transverse waves on a vibrating string are different from sound waves.E! @"itch@ (in music! and freuency have approximately the same meaning.

$1. *n open pipe of length ? is resonating at its fundamental freuency. 9hich statementis correct:

*! -he wavelength is ? and there is a displacement node at the pipeAs

midpoint.

0! -he wavelength is ? and there is a displacement antinode at the pipeAsmidpoint.

7! -he wavelength is &? and there is a displacement antinode at the pipeAs

midpoint.

=! -he wavelength is &? and there is a displacement node at the pipeAsmidpoint.

Note> the waves here are displacement and not pressure waves. +o at each end ofopen pipe, there is a antinode and at its midpointt a displacement node.

$2. -wo speakers are placed side by side and driven by the same freuency of 1'' ;

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7! its freuency is the same as the freuency of an external source.

=! it is oscillating in simple harmonic motion.

&'. * string of mass m and length ? is under tension -. -he speed of a wave in the string

is v. 9hat will be the speed of a wave in the string if the mass of the string is

increased to &m, with no change in length:*! '.1v 0! &v 7! '.3$v =! $.v

&$. 9hen sound passes from air into water*! its freuency does not change.

0! its wavelength does not change.

7! its velocity does not change.

=! all of the above

&&. * sound source approaches a stationary observer. -he freuency heard by the

observer is*! lower than the source.

0! eual to y B ('.1' m! sin (/& t!. 9hat is the maximum speed of the ob4ect:

*! '.6 m/s 0! '.36 m/s 7! '.$ m/s =! '.&2 m/s

&3. 7onsider two pipes of the same length> one is open and the other is closed on one end.

f the fundamental freuency of the open pipe is '' ;

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*! '' ;< 0! 1' ;< 7! $1' ;< =! 2'' ; 32 trombones or $$' cornets: +how your calculations.

GtB 3' d0 #irst need to find the sound intensity (w/m&! of each instrument>

GcB 21d0 G B $' log3' d0GtB 3' d0

+ound intensity for -rombone>

*nd for cornet>

/l#tin t Pr"lem 2 (cntin#ed)

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. Iwang stands beside the tracks as a train rolls slowly past. ;e notes the freuency of

the train whistle is & ;< when the train is approaching him and $ ;< when thetrain is receding from him. +peed of sound in air to be 1 m/s. 9hat is the speed of

the train:

Jiven>

freuencies>f$B& ;< wheref K is the shifted freuency observed bystationary Iwang, andf

f&B$ ;< is freuency emitted by moving source. Use the %vswhen the source

vB 1 m/s is moving toward the observer and Lvswhen the source is moving away from the observer

-here are two =oppler effects> 9ith the train approaching at speed vs, the

observed freuency isf$.

*nd as the train recedes, the observed freuency isf&>

=ividing euation ($! by (&! gives

and solving for the speed of the train yields vsB '/6$ m/s B $.$ km/hr (slow!

1. -he light beam in the figure shown strikes surface & at the critical angle. =etermine

the angle incident i.

+ + 60= 180 = 90 42= 48

= 42

=90 22= 18

Using +nellMs ?aw>

n$sin1= n&sin2

ou need to find n& first> use +nellMs law for the refractionfrom surface & (n$B nairB $!>

n&sin42= n$sin90 n&B $.6

n$sin1= n&sin2 $.' sin1= $.6 sin18

1= sin%$ ($.6 sin18) 1= 27.5

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#or the following problems show your solution on the color papers. 0ut draw the ray

diagrams on the ruler shown for each problem and attach them to your color papers.Oerify your numerical results using your scaled drawn ray diagrams.

2. * small ob4ect is $& cm from a thin positive lens of focal length 2 cm. * plane mirroris placed at the second focal length of the lens and crosses thex-axis as shown. -he

mirror is tilted so the reflected rays do not go back through the lens.

a! =raw a ray diagram to scale showing the final image.b! s the image real or virtual:

c! #ind the position of the final image.

3. Consider a concave mirror with a focal length of 10.0 cm.a) Find the image distance when the object distance is 10.0 cm.b) Find the image distance when the object distance is 5.00 cm.c) Find the magnication of the image for part b).d) Describe the image for part b).

e) Draw the ray diagram for part b) on the rler shown below.

a) /ince the "ect is placed at the cal pint the mirrr% ima3e is rmed atininity (nt +isi"le)

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Pr"lem $ (cntin#ed)

b!

c) The ima3e is +irt#al% #pri3ht% lar3er and n ther side mirrr,

d)

/me 4#estins n 5eat and Thermdynamics,

Please e6plain r sh y#r r* clearly r each the llin3 4#estins r

pr"lems,

$. ou are selling your land by suare feet. f on a hot day you are measuring a plot of

land with a steel tape, will you be making more profit from the land sale: Explain.

+ince the tape is metal, it will expand, and for example $''cm of it now may be $'$cm.

hence the dimensions of actual land are shorter than measured values. Not goodPP

&. 7onsider a cup of tea at room temperature, & '7. f it is heated until it has twice theinternal energy, what is its new temperature:

9hen internal energy doubles, theKelvin temperature of the teawill also double.

-newB &-old where -oldB &3 L & B&63 I-newB &(&63! B 16 I.

-newB 165 % &3 B &1o7 (very hot!

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