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TEST 3 PHYS 104 Due Date: May5th
RULES:(read carefully and ask for clarification if needed):
- This test is to be done at home, individually.You are expected to observe the GMU Honor Code.ANY indication that you have not done the test on your own and violated the Honor Code will result in serious consequences. That includes, but is not limited to failing this test.And if you think I won’t know, think again: I’ve been doing this long enough and I know what each of you is capable of, so rest assured: I will know. If you have any doubts whether something violates the code and/or is considered individual work: ask me.
- You may consult any sources to review pertinent material including all of the course content posted on Blackboard for this class, but you are not allowed to ask for help in actually solving the problems or answering test questions. That includes anyone but me: your classmates, on-line sources, other instructors, LA, a tutor, even your gerbil.
- In an event you have difficulty understanding a test problem, you can ask me for clarification. You can ask me anything, in fact, I just may not answer.
- You can get one free hintfrom me, subsequent hints will cost you. Clarification of what the problem or question asks for is not considered a hint.
- If you do not know how to do some part of a problem, try doing the rest anyway. If necessary pick a value that seems reasonable for the quantity you cannot calculate in a previous part and proceed using that value. Indicate in your work that this is a “made up” value.
- Show your work step by step including detailed calculations, equations you use, and justify any statements you make or no credit will be awarded. Just putting in the final answer without any justification earns you no points. This is actually to your advantage, as it allows me to assign partial credit, when merited.
- Throughout the test use g = 10 m/s2 for acceleration due to gravity on Earth’s surface,
- Unless otherwise stated, use appropriate SI units. And DO use units, I will take points of for lack of units.
- Unless otherwise stated, round your answers to two decimals. The format does not really matter here, I’m a bit smarter than Blackboard and unless it’s something out of this world I can probably figure it out. But remember: I can’t grade what I can’t read(then you get no credit), so keep things legible, neat and well organized. Be succinct and specific.
- Unless you use non-erasable ink you forfeit any right to question me about points awarded for your work.
Please sign below that you agree to abide by these rules.
GOOD LUCK!!!!
1) a) Find the direction of external uniform magnetic field if the force it exerts on a current carrying wire perpendicular to the page is as indicated in the figure below.
Answer:………….……
b) If the wire is 1m long and carries 3A of current, and if magnetic force strength is 9 N what is thismagnitude of this external magnetic field?
Answer:………….……
c) Find the direction of the current in a circular wire loop if the magnetic field it produces in its interior is as shown in the figure below.
Answer:………….……
d) Find the direction of the current in the wire in the figure below that produces the magnetic field directed as shown.
Answer:………….……
e) How far from the wire will the magnetic field strength be 0.1 Gauss if the current flowing through it is 5A?
Answer:………….……
2) a) What would be the direction and magnitude of the force that an external uniform magnetic field B = 7T exerts on an electron which velocity is 3000 m/s directed into the page?
Answer:………….……
Answer:………….……
b) Will this electron
A) move with constant velocity along a straight line
B) move with constant acceleration along a straight line
C) exhibit projectile motion
D) move in a circle
E) move along a spiral
Answer:………….……
c) If you answered D or E what would be the radius of this electron’s circular trajectory?
(mass of electron is me= 9.1110-31 kg)
Answer:………….……
d)EXTRA CREDIT (up to 6 pts)
Three particles with identical massesmand identical initial velocities v0are projected one at a timeinto a region (shaded) in which there is uniform magnetic field Bperpendicular to their velocities as shown in picture below. If two of the particles are deflected from their original directions in opposite ways and third one is not deflected at all, what can you say about the properties of these particles? In figure below dotted lines represent the trajectories of the three particles before and after they enter the magnetic field.
3) You are building a transformer and you want the secondary voltage to be ten times smaller than the primary voltage. (Assume this is an ideal transformer).
a)Which circuit will have to contain solenoid with more turns: primary or secondary? How many more turns exactly? Explain.
Answer:………….……
Answer:………….……
b)Is this a step up or step down transformer?
Answer:………….……
c)What induces the current in the secondary? Discuss in detail all the physical processes involved.
d)In the lab you were instructed to measure the efficiency of the transformer and found that it was less than 1 because
A) not all of the current from the primary flows into secondary
B) not all of the magnetic field produced by current in the primary got transferred inside secondary
C) you used short solenoids
D) it was hard to measure precisely since it moved too fast Answer:……………
e) Why do we need an iron core?
A) to curl our hairand tickle our toes
B) to conduct current from primary to secondary
C) to amplify and transfer electric field from primary to secondary
D) to amplify and transfer magnetic field from primary to secondary
E) to amplify and transfer magnetic field from secondary to primary Answer:……………
f) Can the equipment shown in the figure below be used to step up the voltage from anAA battery? Explain.
Answer:………….……
4) There is a mirror in my car that has a warning stating that “objects in mirror are closer then they appear”. If a 1.6 m tall vehicle located 4 m in front of that mirror produces an image that is 8 cm tall, what kind mirror is this? Find the radius of curvature of this mirror. Supplement your solution with a diagram. Specify the type of image, magnification, and image distance.
Answer:………….……
Answer:………….……
Answer:………….……
Answer:………….……
Answer:………….……
Answer:………….……
5) You placed a 9 cm high object in front of a converging lens with a focal length of 60 cm.
a)if the image distance to the center of the lens is 20 cm find the object distance. (Hint: consider is this a real or virtual image)
Answer:………….……
b)find the magnification.
Answer:………….……
c)find the image height.
Answer:………….……
d)is the image real or virtual?
Answer:………….……
e)is the image upright or inverted?
Answer:………….……
f)is the image reduced or enlarged?
Answer:………….……
g)illustrate your solution with a ray diagram.
6) a) What characteristic of the electromagnetic waves predicted by Maxwell’s theory led him to suggest that light might be an electromagnetic wave? Explain.
b) Which of the following characteristics: speed in vacuum, speed in water, wavelength, and/or frequency, are the same for visible light and radiowaves and which are different? Explain.
c) If the wavelength of a radiowave is 3m what is its frequency?
Answer:………….……
7) Due to electron transition from n = 6 to n = 2 energy state hydrogen atom emits a photon. Use Bohr model of hydrogen atom to answer the following questions.
a)what is the energy of the electron before transition?
Answer:………….……
b)what is the energy of the electron after the transition?
Answer:………….……
c)what is the energy of the emitted photon?
Answer:………….……
d)what is the frequency of the emitted photon?
Answer:………….……
e)what is the wavelength of the emitted photon?
Answer:………….……
f)is the emitted photon in the visible part of the spectrum?
Answer:………….……
g)how much energy was required to ionize this hydrogen atom prior to transition i.e. when n=6?
Answer:………….……
h)what was the radius of the electron’s orbit prior to transition i.e. when n=6?
Answer:………….……
8) a) A cube with sides 10 m each as measured in its rest reference frame passes by an observer on Earth with a speed of 0.995c parallel to one of its sides. What dimensions will the observer on Earth measure?
Answer:………….…by ……………… by ……………….
b) An observer on Earth notes that an astronaut on a spaceship cooks an egg for 21 minutes. Astronaut disagrees and claims that he only cooked the egg for 3 minutes. How fast is the spaceship moving with the respect to the observer on Earth?
Answer:………….……
c) If you could convert mass to energy with 100 % efficiency, how much energy could generate out of 1 kg of mass?
Answer:………….……
d) Spaceship USS Enterprise approaches Earth with the speed of 0.999c. A message encoded in a laser beam is sent from the ship to Earth. What is the speed with which the encoded signal travels as
i) measured by an observer on Earth
Answer:………….……
ii) measured by the astronauts on board the spaceship
Answer:………….……
EXTRA CREDIT (up to 10 pts)
Light incident from air strikes a diamond at 30 as shown in figure below.
a)At what angle to the normal a is the light reflected back into air? (find r)
Answer:………….……
b)At what angle to the normal a is the light refracted inside the diamond? (find 2)
Answer:………….……
c)At what angle to the normal b is the light incident on the back side of the diamond? (find 3)
Answer:………….……
d)At what angle to the normal b is the light reflected on the back side of the diamond? (find 5)
Answer:………….……
e)At what angle to the normal b is the light refracted back into air on the back side of the diamond? (find 4)
Answer:………….……
SHORT ESSAYS:
a) Choose two of the following topics and explain physicsinvolved in that phenomena. Only two topics will be graded and I will not read more than two, so clearly indicate which ones you chose or I will assume it’s the first two and grade accordingly. These are to be SHORT essays so don’t go overboard!!!! (alsosee instructions on page 1.)Supplement your answers with appropriate sketches!!!!!!.
a) In class I’ve shown you a video of aurora. Discuss in detail physical processes involved in aurora formation and why is it usually seen only in extreme northern and southern latitudes.
b)Discuss in detail physics involved in the rainbow formation.What kinds are there?
c)Explain why the sky is blue and why the clouds are white. Why do the colors change at sunset?
d) What is a mirage? Discuss in detail how it forms. What kinds are there? Give examples of different types.
Essay 1
Topic:………………………………………………………………………………………………………
Essay 2
Topic:………………………………………………………………………………………………………
QUESTIONS: CAREFULL! For some questions there may be more than one correct
answer. Choose them all for full credit.
1) In lab you were asked to perform a series of actions such as inserting and removing a permanent magnet inside two solenoids N = 1600 and N = 400. Which of the following statements is not true?
A)inserting the south pole resulted in voltage of opposite sign than inserting the north pole
B)the voltage induced depended on the number of turns in the solenoid
C)there was voltage induced when magnet and solenoids were both stationary
D) inserting the magnet induced the voltage opposite then removing the magnet
E) moving the solenoid induced voltage and so did moving the magnet Answer: ………………
2) If a mirror produces an inverted virtual image that mirror is
A) flat
B) concave
C) convex
D) such mirror doesn’t exist Answer:………….…….
3) If an image produced by a lens is real and upright that lens is
A) converging
B) diverging
C) raging
D) such lens doesn’t exist Answer:………….……
4) In a vacuum, the velocity of electromagnetic waves
A) is infinite
B) is constant
C) depends on wavelength
D) depends on the frequency
E) depends on amplitude
F) gets all sucked up Answer:………….……
5) In translucent medium, such as water or glass, the velocity of electromagnetic waves
A) is constant and equal to 3×108m/s
B) is constant and higher than 3×108m/s
C) is constant and lower than 3×108m/s
D) depends on wavelength
E) exceeds the speed limit Answer:………….……
6) In a series of brilliant experiments conducted in 1880s Heinrich Rudolf Hertz
A) confirmedthat light is an electromagnetic wave
B) confirmedexistence of electromagnetic waves other than visible light
C) confirmedlongitudinal nature of electromagnetic waves
D) confirmed that LC circuits cannot produce electromagnetic waves Answer:………….……
7) When you see an inverted image of an approaching car on a wet roadway this image is produced by
A) refraction
B) mirage
C) reflection
D) dispersion
E) coercion Answer:………….……
8) A halo
A) is formed by dispersion of light rays on hexagonal ice crystals
B) circles the sun or the moon at 22 from their center
C) is sometimes accompanied by sundogs
D) all of the above
E) is sometimes fetched by the dogs Answer:………….……
9) Which of the following have highest frequencies
A) visible
B) infrared
C) ultraviolet
D) microwaves
E) convection ovens
F) toasters Answer:………….……
10) Astronauts are packing for a trip to a distant star to which they will travel at 0.99c. If the floors in the space ship run parallel to the ship’s velocity they should purchase
A) smaller sizes of clothing because they’ll be skinner on the trip
B) larger sizes of clothing because they’ll be fatter on the trip
C) shorter sizes of clothing because they’ll be shortened on the trip
D) longer sizes of clothing because they’ll be elongated on the trip
E) none of the above Answer:………….……
11) As viewed by a stationary observer time measured by clock in motion is
A)contracted
B)dilated
C)needs a new kidney
D)contracted an infectious disease Answer:………….……
12) Suppose the astronauts were paid per hour of time spent in space. Which would benefit them more
A) if the clock is put on their spaceship
B) if the clock stays on Earth
C) it won’t make any difference
D) they should just volunteer their time Answer:………….……
13) Thomas Young’s is famous for his double slit experiment because it
A) has shown that electrons were particles
B) has shown that electrons were waves
C) has shown that light was made of particles
D) has shown that light was a wave
E) made him forever young Answer:………….……
14) A toilet on a spaceship moving close to the speed of light
A) will be hard to use because it will be too narrow
B) will be hard to use because it will become too shallow
C) will run in reverse
D) will take forever to flush
E) will serve its function as normal Answer:………….……
15) A star is located 1000 light years away from Earth. Which statement is true
A)we can’t ever reach that star within human lifespan
B)we can only reach that star within human lifespan if we travel faster than light
C)we can reach that star if we travel close to the speed of light due to time dilation and length contraction but we cannot ever return to Earth
D)we can reach that star if we travel close to the speed of light due to time dilation and length contraction but we cannot return to Earth within the lifespan of our contemporaries
Answer:………….……
16) Which is false?
A) the experiments performed on a spaceship accelerating through empty space at 9.8 m/s2 will give the same results as experiments performed on Earth.
B) time runs more slowly on the surface of the Sun than it does here on Earth
C) two parallel lines can never intersect (even in curved spacetime)
D) massive objects bend the path of light passing by them Answer:.………….……
17) According to the Bohr model of the hydrogen atom, when an electron jumps from energy level where n = 4 to where n = 1
A) electron jumps for the sheer joy of it
B) a photon is emitted.
C) a photon is absorbed.
D) electron is emitted.
E) electron is absorbed
F) none of the given answers Answer:………….……
18) We say that an atom is excited if its electron
A) feels enjoyment or pleasurable anticipation
B) is physically aroused
C) just gobbled a photon
D) just emitted a photon
E) relaxes in the ground state (aaah!) Answer:………….……
19) According to the Bohr model of the hydrogen atom
A) an electron in ground state can absorb a photon with wavelength of 410 nm
B) an electron in great shape can absorb a photon with wavelength of 410 nm
C) an electron in n=2 excited state can absorb a photon with wavelength of 410 nm
D) an electron in n=3 excited state can absorb a photon with wavelength of 410 nm
E) an electron in n=4 excited state can absorb a photon with wavelength of 410 nm
F) such photon cannot not be absorbed at all by a hydrogen atom Answer:……………….
20) According to the Einstein’s theory of General Relativity
A) gravity is a force of attraction between two masses
B) gravity is a force of attraction between two charges
C) gravitydoes not exist; there is only thecurvature of spacetime
D) gravity is caused by relativistic speeds Answer:……….….……
You’re done!!! THE END!!!!