Which of the following explains best summarizes the dark matter?

The matter that is identified by its gravitational properties only, not by observation through any electromagnetic wave in the spectrum.

The matter found in the darker areas of the universe where nothing can be seen.

The matter, that is made up of black holes

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Bunny GreenfelderLv2

4 Jul 2019

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Electromagnetic radiation is emitted when a charged particle movesthrough a medium faster than the local speed of light. Thisradiation is known as Cerenkov radiation. Cerenkov radiation isfound in many interesting places such as particle detectors andnuclear reactors and can even be seen by astronauts when cosmicrays traverse their eyes. It should be stressed that the particleis never going faster than the speed of light in vacuum (or c),just faster than the speed of light in the material (which isalways less than c). The creation of Cerenkov radiation occurs inmuch the same way that a sonic boom is created when a plane ismoving faster than the speed of sound in the air. The variouswavefronts that propagate in the material add coherently to createan effective shock wave. In this problem, you will become familiarwith this type of radiation and learn how to use its properties toget information about the particles that created it.
A)What is the threshold velocity v_threshold (water) (i.e., theminimum velocity) for creating Cerenkov light from a chargedparticle as it travels through water (which has an index ofrefraction of n=1.33)?
v_threshold (water) =c
B)What is the threshold velocity v_threshold (ethanol) for creatingCerenkov light from a charged particle as it travels throughethanol (which has an index of refraction of n=1.36)?
v_threshold (ethanol) =c
C)Which of the following best explains why neutrally chargedparticles can't give off Cerenkov radiation?

a)Neutral particles are too heavy to emit radiation.
b)Neutral particles don't interact with the electromagnetic fieldsof the medium.
c)Neutral particles can't move above the threshold velocity forCerenkov radiation.
d)Charged particles hit the nuclei of the material more often andthus create more radiation

Hi everyone,
I'm International Students and I have difficault to understand someproblems in physics. I want to do extra work to be ready forMidtearm.
Please if there is any one can help me by showing me how to solveit.
and if u can show me the steps because I will use it asnotes.

1-What are the metric prefixes for ten and tenth?

2-If you multiplied 7774 m by 36 m, how many significant figuresshould you report in your answer?

3-A ball is dropped:
What is its initial speed?
What is the magnitude of its initial acceleration?

4-A jogger jogs two blocks directly north.
(a) How do the jogger's average speed and the magnitude of theaverage velocity compare?
average speed ( ) magnitude of average velocity
(b) If the jogger's return trip follows the same path, how doaverage speed and magnitude of the average velocity compare for thetotal trip?
average speed ( ) magnitude of average velocity

5-A child's cubic play block has a mass of 115 g and sides of 5.2cm. When placed in a bath tub full of water, will the cube sink orfloat?
(sink) or (float)

6-A ball with a radius of 8 cm and a mass of 550 g is thrown into alake. Will the ball sink or float?
(sink) or (float)

7-Persons A and B do the same job, but B takes longer
Who does the greater amount of work?
person A, person B, Or all the same
Who is more "powerful"?
Person A or Person B

8- Which two renewable energy sources depend on the weather?(Select all that apply.)
geothermal
biomass
tidal
solar
wind

9- The two common liquids used in liquid-in-glass thermometers arealcohol (ethanol) and mercury, which have melting points andboiling points of -114Â°C, 79Â°C and -39Â°C, 357Â°C,respectively.
Which one of these thermometers would be better for low temperaturemeasurements?
(alcohol or mercury)
Which one of these thermometers would be better for hightemperature measurements?
(alcohol or mercury)

10-What determines the phase of a substance? (Select all thatapply.)
humidity
temperature
amount of the substance
pressure

11-What is the difference between a longitudinal wave and atransverse wave?

Longitudinal wave: particle displacement is (---) parallelperpendicular to wave velocity.
Transverse wave: particle displacement is ( ------) perpendicularparallel to wave velocity.

Give an example of a longitudinal wave.
(sound wave in air OR
light wave)
Give an example of a transverse wave.
(sound wave in air Or
light wave)

12-Which end (blue or red) of the visible spectrum has the shorterwavelength?
Which has the lower frequency?

13- How long does the image of a 18-in ruler appear in a planemirror?
Does this depend on the distance the ruler is from themirror?
(Yes OR
No)

14-What optical phenomenon causes soap bubbles and oil slicks toshow colorful displays?

15- Which two particles that make up atoms have about the samemass? (Select all that apply.)
protons
electrons
neutrons

16- Which two have the same magnitude of electric charge? (Selectall that apply.)
neutrons
electrons
protons

17- Name one phenomenon that can only be explained by light havinga wave nature.
polarization
photoelectric effect
acceleration
displacement

18- How are frequency and wavelength of an electromagnetic waverelated?
higher the frequency, longer the wavelength
higher the frequency, shorter the wavelength
the frequency and wavelength are not direclty related

19- What other name is often used to refer to the electron cloudmodel of the atom?
plum pudding model
billiard ball model
quantum model
nuclear model
planetary model

20- What are the names of the elements with the followingsymbols?
(a) Ne
(b) Li
(c) He

21- After 4 half-lives have gone by, what fraction of a sample of aradioactive isotope remains? (Write your answer in fractionform.)

22- What are the most common names for these compounds andions?
(a) N2O
(b) HCl
(c) C2H3O2 ?
(d) PO43-

23- What is the formula for the common household compound known astable salt? (Type your answer using the format CO2 for CO2.)

24- What element has the lowest electronegativity?
What element has the second highest electronegativity?

Give the Stock system name for the following.
(a) Cr(OH)2
(b) CuCl2
(c) AuBr3

If a virtual image is formed 9.0 cm along the principal axis from aconvex mirror of focal length â15.0 cm, how far is the object fromthe mirror?

2. A woman looking in a makeup mirror sees her face at twice itsactual size and right-side up. If she is 26.0 cm from the mirror,what is its focal length?

3. Which of the following best describes the image of a concavemirror when the object is at a distance greater than twice thefocal point distance from the mirror?
a. virtual, upright and magnification greater than one
b. real, inverted and magnification less than one
c. virtual, upright and magnification less than one
d. real, inverted and magnification greater than one

4. A convex mirror with focal length of ?18 cm forms an image 12 cmbehind the surface. Where is the object located as measured fromthe surface?

5. A convex mirror with a focal length of ?18 cm forms an image 15cm behind the surface. If the object height is 1.2 cm what is theimage height?

6. An object placed 14 cm from a concave mirror produces a realimage 8.0 cm from the mirror. If the object is now moved to a newposition 18.0 cm from the mirror, where is the new image located asmeasured from the mirror?

7. When the reflection of an object is seen in a concave mirror theimage will:

8. A candle is 40.0 cm in front of a convex spherical mirror ofradius of curvature 70.0 cm. What are the image distance and themagnification, respectively?

9. An object is 16.0 cm from the surface of a spherical Christmastree ornament that is 8.00 cm in diameter. What is themagnification of the image?

10. A solid glass sphere with a radius of 6.00 cm and index ofrefraction of 1.50 has a small coin embedded 3.00 cm from the frontsurface of the sphere. For the viewer looking at the coin throughthe glass, at what distance from the front surface of the glassdoes the coinâs image appear to be located?

11. A glass block, for which n = 1.52, has a blemish located 4.5 cmfrom one surface. At what distance from that surface does the imageof the blemish appear to the outside observer?

12. An object of length 2.00 cm is inside a plastic block withindex of refraction 1.50. If the object is viewed from directlyabove, what is the length of its image?

13. An object is placed at a distance of 25 cm from a thin convexlens along its axis. The lens has a focal length of 10 cm. What arethe values, respectively, of the image distance andmagnification?
14. An object is placed at a distance of 50 cm from a thin lensalong the axis. If a real image forms at a distance of 35 cm fromthe lens, on the opposite side from the object, what is the focallength of the lens?

15. A contact lens is made of plastic with an index of refraction1.50. The lens has an outer radius of curvature of +2.0 cm and aninner radius of curvature of +2.5 cm. What is its focallength?

16. A Youngâs double slit has a slit separation of 2.50 ? 10?5 m onwhich a monochromatic light beam is directed. The resultant brightfringes on a screen 2.00 m from the double slit are separated by2.30 ? 10?2 m. What is the wavelength of this beam? (1 nm = 10?9m)

17. A Youngâs double-slit apparatus is set up so that a screen ispositioned 1.9 m from the double slits, and the spacing between thetwo slits is 0.040 mm. What is the distance between alternatingbright fringes on the screen if the light source has a wavelengthof 630 nm? (1 nm = 10?9 m)

18. The blue tint of a coated camera lens is largely caused by whateffects?

19. What is the minimum thickness of a glycerin film (n = 1.47) onwhich light of wavelength 650 nm shines that results inconstructive interference of the reflected light? Assume the filmis surrounded front and back by air.

20. Light of wavelength 560 nm is incident on a slit of width 0.150mm, and a diffraction pattern is produced on a screen that is 2.00m from the slit. What is the width of the central bright fringe? (1nm = 10?9 m)

21. Light of wavelength 610 nm is incident on a slit of width 0.25mm, and a diffraction pattern is produced on a screen that is 1.5 mfrom the slit. What is the distance of the second dark fringe fromthe center of the bright fringe? (1 nm = 10?9 m)

22. A multiple slit diffraction grating has a slit separation of2.50 ? 10?6 m. Find the wavelength of the monochromatic light thatwill have its second order bright fringe diffracted through anangle of 38.0Â°. (1 nm = 10?9 m)

23. A diffraction grating with 12 000 lines/cm will exhibit thefirst order maximum for light of wavelength 510 nm at what angle?(1 nm = 10?9 m)

24. A beam of unpolarized light in air strikes a flat piece ofglass at an angle of incidence of 58.0Â°. If the reflected beam iscompletely polarized, what is the index of refraction of theglass?

25. A beam of polarized light of intensity I0 passes through asheet of ideal polarizing material. The polarization axis of thebeam and the transmission axis of the sheet differ by 45Â°. What isthe intensity of the emerging light?

26. At what angle is the sun above the horizon if its light isfound to be completely polarized when it is reflected from the topsurface of a slab of glass (n = 1.65)?

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