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Why are lower energy photons filtered out in medical x-ray imaging?

A. They are quickly attenuated by tissue and therefore do notpenetrate the body well.
B. They do not contribute to the image formation.
C. They only contribute to the patient exposure to the harmfulradiation.
D. All of the above are reasons why these photons are filteredout.

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Physics: Principles with Applications
7th Edition, 2013
Giancoli
ISBN: 9780321625922

Related questions

Students are designing an experiment to demonstrate the conversionof mechanical energy into thermal energy. They have designed theapparatus shown in the figure above. Small lead beads of total massM and specific heat c (heat capacity is used in Q = mc?T) fill thelower hollow sphere. The valves between the spheres and the hollowtube can be opened or closed to control the flow of the lead beads.Initially both valves are open.

a. The lower valve is closed and a student turns the apparatus 180°about a horizontal axis, so that the filled sphere is now on top.This elevates the center of mass of the lead beads by a verticaldistance h. What minimum amount of work must the student do toaccomplish this?

b. The valve is now opened and the lead beads tumble down thehollow tube into the other hollow sphere. If all of thegravitational potential energy is converted into thermal energy inthe lead beads, what is the temperature increase of the lead?

c. The values of M, h, and c for the students' apparatus are M =3.0 kg, h = 2.00 m, and c = 128 J/(kg · K). The students measurethe initial temperature of the lead beads and then conduct 100repetitions of the "elevate and drain" process. Again, assume thatall of the gravitational potential energy is converted into thermalenergy in the lead beads. Calculate the theoretical cumulativetemperature increase after the 100 repetitions.

d. Suppose that the experiment were conducted using smallerreservoirs, so that M was one tenth as large (but h was unchanged).Would your answers to parts (b) and (c) be changed? If so, in whatway, and why? If not, why not?

e. When the experiment is actually done, the temperature increaseis less than calculated in part (c). Identify a physical effectthat might account for this discrepancy and explain why it lowersthe temperature.

















1. The Jeans instability occurs when
Athe pressure in a gascloud is less than its gravitationalforce.
Bthe pressure in a gascloud is greater than its gravitationalforce.
Cthe temperature in acollapsing cloud is hot enough to fuseHydrogen.
Dthe temperature in acollapsing cloud is hot enough to fuse Helium.

2. At what stage in its life does a star pass through theprotostarphase?
AAfter condensationbut before nuclear reactions begin in itscore.
BWhile it is convertinghydrogen into helium in its core.
CAfter nuclear reactionsend in its core, but before the red giantphase.
DWhen it is expanding insize as a red giant or supergiant.
3. The characteristics of an open cluster of stars are
Aa few hundredmembers, often very young and still embedded in thegas and dustfrom which they were formed.
Bmany thousand members, ofdifferent ages.
Ca few dozen members, theremnant of a globular cluster of starsfrom which most of themembers have escaped.
Dhundreds of thousands ofmembers, all very old, and no or verylittle interstellar gas anddust.
4. What is a protostar?
AA star near the endof its life, before it explodes as asupernova.
BA sphere of gas aftercollapse from an interstellar cloud butbefore nuclear reactionshave begun.
CA small interstellarcloud, before it collapses to become astar.
DA shell of gas left behindfrom the explosion of a star as asupernova.
5. What is an H II region?
AA region of hot,ionized hydrogen around one or more O and Bstars.
BA region of molecularhydrogen inside a giant molecularcloud.
CA region of neutral,atomic hydrogen in interstellar space.
DA region of gas and dustformed by the explosion of a massive star.
6. The total time that the Sun will spend as a main sequencestaris
Aabout 4.5 millionyears.
Bat least 200 billion yearsyears.
Cabout 1 millionyears.
Dabout 10 billionyears.
7. How is a star's lifetime related to its mass?
AThe lifetimes ofstars are too long to measure, so it is not knownhow (or if) theirlifetimes depend on mass.
BA star's lifetime does notdepend on its mass.
CLower-mass stars runthrough their lives faster and have shorterlifetimes.
DHigher-mass stars runthrough their lives faster and have shorterlifetimes.
8. In the Hertzsprung-Russell diagram, how does the position ofatypical star change while it is at the main sequence phase ofitsevolution?
AA star's position onthe main sequence is determined only by itsmass and not its age,and so, stars do not move along the mainsequence duringevolution.
BMassive stars (4 solarmasses) move toward the upper left as theirluminosity increases,while lower-mass stars move toward the lowerright as theirtemperature decreases.
CStars move from upperright to lower left while they are on themain sequence.
DStars move from upper leftto lower right while they are on themain sequence.
9. Why does the core of the Sun contain more helium andlesshydrogen than does the surface of the Sun?
AHelium condenses moreeasily so, when the Sun was forming the corebecame helium-rich;vast quantities of hydrogen were added onlyafter the core becamemassive enough.
BThe hydrogen has beenlifted out of the core by the Sun's magneticfield.
CHelium is heavier thanhydrogen, and has sunk toward the center ina process of chemicaldifferentiation.
DThermonuclear reactionshave converted much of the originalhydrogen in the core intohelium.
10. In terms of nuclear reactions, what is the next stage ofastar's life after the end of hydrogen burning in thecore?
AHydrogen burning ina thin shell around the core.
BHelium burning in thecore.
CCarbon burning.
DDeath (it becomes eithera supernova or a white dwarf).

1. A physical therapy patient contracts her biceps muscle, andexerts a horizontal force of 180 N on the spring shown in thefigure at right. Assume the forearm rotates at the elbow. a) Drawan extended force diagram of the forearm (everything from the elbowto the tip of the fingers) showing the pivot point and all of theforces acting on the forearm where they actually are applied. Youwon’t know the magnitudes (or even the directions) of these forcesuntil you finish the whole problem but just draw reasonable vectorsfor now.
b) Now draw a force diagram with the forearm as a dot. c) Use thefact that the forearm is perfectly stationary at all times to findthe horizontal force that her biceps exerts on her forearm AND theforce exerted by the bone of the upper arm (shown below the biceps)on the forearm (weight = 30N). Note that muscles can only PULL inthe direction along the muscle, but that ligaments (like the onesin the elbow that connect the upper arm with the forearm) can exertforces in any direction. d) Briefly explain in complete Englishsentences (i.e., not just equations) why the bone of the upper armexerts such a large force on the forearm. e) What is the advantageof having the point where the biceps is attached to the forearm soclose to the elbow? What is the disadvantage of having it attachedso close?

2. You are trying to roll your bicycle wheel (of mass m andradius R) over a curb (of height h). To do this, you apply ahorizontal force F in the direction of desired motion. What is theminimum magnitude of the force that will successfully raise thewheel onto the curb when the force is applied (a) at the center ofthe wheel, and (b) at the top of the wheel? (c) In which case isthe magnitude of the force the least?

3. A hay bale is being dragged along a horizontal surface withconstant speed by a force F. The hay bale is 0.6 m high, 0.3m wide,and 0.9 m long (the side the force is applied to, perpendicular tothe direction of motion). The coefficient of kinetic friction is0.33. (a) Find the magnitude of the force, F. (b) Find the height,h, at which the bale will begin to tip over if the force is appliedat that height.

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