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AP Physics > Chapter 27 > Flashcards

Chapter 27 Flashcards

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1
Q

A compass needle is not always balanced parallel to the earth’s surface but one end may dip downward explain

A

The compass needle aligns itself with the local magnetic field of the earth and the earth’s magnetic field lines are not always parallel to the surface of the earth since the earth is not a uniform circle (mountain ranges)

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2
Q

A horse show magnet is held vertically with the North Pole on the left and South Pole on the right a wire passing between the poles equidistant from them carries a current directly away from you in what direction is the force on the wire

A

Down

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3
Q

In teh relation F=IL X B which parties of vectors (F L B) are always at 90 degress which can be at other angles

A

F is always perpendicular to both B and length. B and length can be at any angle with respect to each other.

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4
Q

The magnetic field due to current in wires in your home can affect a compass. Discuss the effect in terms of currents including whether they are ac or dc

A

Ac (alternating current) has no effect on the compass needle due to rapid change of direction of current (60 Hz) and the B surrounding it. dc (direct current) will deflect the compass needle since the current I is traveling in one direction. The deflection depends on the B and the direction of the current. Use the right hand rule to determine the direction of deflection. NOTE: the effect on the compass decreases with increasing distance from the wire).

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5
Q

If a negatively charged particle enters a region of uniform magnetic field which is perpendicular to teh particles velocity will the kinetic energy of the particle increase decrease or stay the same? Explain

A

KE of the particle will remain the same. Mag force on the particle will be perpendicular to the particles velocity and so no work will be done on the particle. The force will change the direction, so the velocity vector changes to provide centripetal acceleration but the SPEED does not change.

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6
Q

Explain why a strong magnet held near a CRT television screen causes the picture to become distorted also explain why the picture sometimes goes completely black where the field is the strongest

A

The picture is created when moving electrons hit the back of the screen. A strong magnet held near or on the screen can deflect the electrons from their path of imprinting on the back of the screen.

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7
Q

Can you set a resting electron into motion with a steady magnetic field, with an electric field

A

No, you cannot set a resting electron into motion with a static magnetic field. In order for a charged particle to experience a magnetic force (Lorentz force) it must already have a velocity component perpendicular to the magnetic field. F=qvBsintheta if v=0 then F=0,Yes you can set an electron into motion with an electric field the electric force on a charged particle does not depend on the velocity F=qE.

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8
Q

A charged particle is moving in a circle under the influence of a uniform magnetic field if an electric field that points the same direction as the magnetic fied is turned on describe the path the charged particle will take

A

The particle will move in a helical path in the direction electrons of the electric field

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9
Q

A charged particle moves Ina straight line through a particular region of space could there be a nonzero magnetic field in this region if so give two possible situtations

A

Yes, the B could be parallel or anti parallel to the velocity of the charged particle. The magnetic force would be zero and the particle would continue moving in a straight line due to Newton’s first law of motion.

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10
Q

If a moving charged particle is deflected sideways in some region of space can we conclude for certain that B doesn’t equal 0 in that region

A

No, a charged particle may be deflected sideway by an electric field if a component of its velocity is perpendicular to field.

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11
Q

How could you tell whether moving electrons in a certain region of space are being deflected by an electric field on a magnetic field or by both

A

If the direction of the velocity of the electrons is changing but their speed is not (kinetic energy stays the same) then they are being deflected by a magnetic field only and their path way will be circular. If the speed of the electrons is changing but the direction is not then they are being accelerated by an electric field only. If both the speed and the direction are changing, the particles are possibly being deflected by both an electric and a magnetic field or they are being deflected by an electric field that is not parallel to the initial velocity of the particles.

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12
Q

What dos the field do when there is a constant magnetic field acting on a charged particle

A

Field accelerates the particle

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13
Q

A beam of protons is `

A

Current

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14
Q

What is speed of lgiht and can anything go faster than that

A

10^8 and no

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15
Q

A current in a long straight wire produces a magnetic field and these magnetic field lines

A

Form circles which go around the circle

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16
Q

Consider two long straight parallel wires each carrying a current I if hte currents are flowing in opposite directions

A

The two wires repel each other

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17
Q

A proton is released such that its initial velocity is from left to right across this page the protons path however is deflected in a direction toward the bottom edge of the page due to the presence of a uniform magnetic field what is the direction of this field

A

Out of hte page

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18
Q

Geophysicists today generally attribute the existence of the earths magnetic field to

A

Convection currentns with liquid interior

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19
Q

Magnetic declination means

A

Angle between directs to true north and magnetic north

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20
Q

The magnetic field of hte eart is believed responsible for which of teh following

A

Deflecting of charged cosmic rays

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21
Q

Assume that a uniform magnetic field is directed into this page if an electron is released with an initial velocity directed from the bottom edge to the top edge of the page which of teh following describes the direction of the resultant force acting on the electrons

A

To the right

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22
Q

The path of a charge particle moving parallel to a uniform magnetic field will be whcih of the following

A

Straight line

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23
Q

The magnetic domains in a nonmagnetized piece of iron are characterized by whcih orientations

A

Random

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24
Q

The force on a charged particle created by its motion in a magnetic field is max at what angle between the parole velocity and field

A

90 degrees

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25
Q

The force exerted on a current carrying wire located in an external magnetic field is directly proportional ot which of the following

A

Current strength and field strength

26
Q

The direction of the force on a current carrying wire located in an external magnetic field is

A

Perpendicular ot the field and current

27
Q

A 2 m wire segment caring a current of .6 A oriented parallel to a uniform magnetic field of .5 T experiences what froce `

A

Zero

28
Q

A certain charge radiates na electric field a force will be exerted on it when it

A

Travels in a path normal to a magnetic field

29
Q

A positive charge Entersa magnetic field and travels parallel to but opposite the field the charge feels or experiences

A

No force because moving parallel and you need a velocity that is perpendicular or no force

30
Q

The ratio of an alpha particle to taht of a proton is

A

2 alpha particle : 1 proton

31
Q

A charged particle can move through a mnagetic field without a force only when it is

A

Parallel

32
Q

Can teh kinetic energy of a charged particle be increased by a magetnci force

A

NO

33
Q

How do the magnetic field lines de to current carrying wires radiate from teh wire

A

In circles around the wire

34
Q

As the length of a current carrying wire within a uniform magnetic field doubles teh force on teh wire

A

Doubles

35
Q

The magnetic field due to current in wires in tour home can affect a compass. Are current ac ro dc adn their distance away

A

Dc will affect teh compass by teh ac will not

36
Q

Compare and contras the magnetic field due to a long straight current and the electric field due to a long straight line of electric charge at rest

A

B forms circles around the wire and the E field will point outward for + charges and inward for - charges. The E field due to a long straight line of electric charge at rest is proportional to charge per unit length. B due to a long straight current is proportional to current I strength. Both fields are inversely proportional, inverse square laws, to the distance from the wire or line of charge.

37
Q

Two insulated long wires caring equal currents I cross at fifth angles to each otehr. Describe magnetic force one exerts on tehother

A

The B force exerted on one wire by ht either wire try to align the wires forces will be equal and opposite becuase of newtons third law but eh net torque is zero

38
Q

A horizontal wire carries a large current a second wire carrying a current in teh same direction is suspended below it can teh current in teh upper wire hold the lower wire in suspension against gravity under whta conditions will the lower wire be in equilibrium

A

Yes assume teh upper wire is in a fixed position,since I is in teh same direction the wires will tract each tower the lower wire will be held in equilbirum if this force of attraction upward is eaqal in magntiduce to tehweight of the wire downward

39
Q

A horizontal currentt carrying wire free to move in earths gravitational field is suspended directly aboce a second parallel current carrying wire in what direction is the current in teh lower wire can teh upper wire be held in stable equilibrium due to teh magnetic force of the lower wire

A

The I in teh lower wire will be in opposite anti paralllel direction to teh I in teh upper wire, teh upper wire can be held in equilbrium due to the balance between B force f4rfom the lower wire adn teh gravity froce

40
Q

What would be the effect on B inside a long solenoid if teh diameter of all teh loops was doubled, or the spacing between loops was doubles of the solenoid length was doubled along with a doubling in teh total nunmber of loops

A

The diameter has no effect, if the spacing doubles then so number of loops decreases by 2 so teh B decreases by 2, it remains teh same bc its 2/2 which is 1

41
Q

biot savards law

A

The Biot Savart Law states that the net field at a point in space is a vector sum of the field contributions due to each infinitesimal current element.

42
Q

Is B teh same for all points in a plane

A

No B varies in strength due to teh distance, it is the strongest in teh center of teh loop

43
Q

Why does twistin gthe lead in wires to electrical devices reduce the magnetic effects of teh leads

A

By twisting the wires the B field of the opposing wire will cancel and eliminate any stray B field that could interfere with any other close current carrying wire.

44
Q

Compare biot savarts law with coulumbs law

A

They are both inverse square laws in that the force decreases inversely prop to the square on the distance. They both have proportional constants. Coulumb’s Law describes a central force (particles move in a straight line toward or away from another particle) and Biot-Savart involves a cross product of vectors so it cannot describes a central force but only a centripetal force.

45
Q

A heavy magnet attracts from rest a heavy block of iron before striking teh magnet the block has acquired condiable kinetic energy what is the source of this kinetic energy when teh blocks trikes the magnet some of teh letters domains may be jarred into rando,ness decscribe the energy transformations

A

Source of KE is the attractive force produced by the B field from the magnet acting on the magnetic (domains) in the soft iron. When the block strikes the magnet, some of the KE from the block is converted into KE in the iron atoms in the magnet randomize get their magnetic moments and decreasing the overall field produced by the magnet. Some of the KE of the block as a whole is also converted into thermal energy. The total amount of energy must be conserved.

46
Q

Will a magnet attract any metallic object such as aluminum or only those made of iron and why

A

Al is not magnetic because it’s domains are random. The spin of the electrons are random for iron it is magnetic becuase the spin of the electrons line up so the domains are not random.

47
Q

An unmagnetized nail will not attarc an unmagnetized paper clip however if one end of the nail is in contact with a magnet the other end will attract a paper clip

A

When one end of a nail (Fe) is in contact with a magnet, some of the domains in the nail align, extending the magnetic effect of the magnet into the nail and then extending the B into the paper clips. The nail and paper clips will be equally attracted to either end of the magnet.

48
Q

Can an iron rod attract a magnet can a magnet attract an iron rod what msust you consider to answer

A

Yes, third law applies. Forces are equal and opposite on two different objects.

49
Q

Why will either pole of a magnet attract an unmagnetized piece of iron

A

It aligns the domains in the magnet. The N and S pole are equal in strength.

50
Q

Suppose you have three ron rods two of which are magnetized byt the third is not how would you determine which two are the magnets without using any additional objects

A

Trial and error until you find the two that repel each other still won’t know what poles you have but will know that you have two magnets.

51
Q

Two iron bars attract each toher no mattter which ends are paced close togetehr are both magnets

A

NO one is a a magnet and the other isnt

52
Q

Whcih of teh following will a produce a magnetic field

A

A magnet, teh eart adn moving electric curve add an electric current

53
Q

When charged particles mvoe parallel to teh direction of a magnetic field the particle travels in a

A

straight lune becuase it is parallle so no toque

54
Q

As a proton moves through space it creates

A

Both an electric and magnetic field

55
Q

Can a magnetic force be exerted only if the particle is mvoing

A

True

56
Q

Does the magnetic field of a current carrying wire exist only if the current in teh wire is changing

A

No

57
Q

For a charged particle a constant magnetic field cna be used to change

A

Only the direction of teh particles velocity

58
Q

A wire carries a current directly away from your hcih way do teh magnetic field lines produced by w=this wire point

A

They make circles around the wire

59
Q

A proton eneters a uniform magnetic field that is perpendicular to teh patrons velocity what happens to teh kinetic energy of teh proton

A

It stays teh same becuase the centripetal froce acan only change when Toby changing teh direction noteh velocity

60
Q

The magnetic field depends on

A

Particle charg particles velocity and strength of teh external magnetic field

61
Q

Two paralle wires are vertical teh one ont he left carries a 10A current upward the other carries 5A current cowards compare teh magnitude of teh force that each wire exerts on teh other

A

The two wires exerted teh same foc eon each other bc Newton third law adn teh direction is reeling each toehr teh magnetic field isnt the dame becuase it is dependent on teh current

AP Physics (4 decks)

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