Chapter 27 Flashcards
A compass needle is not always balanced parallel to the earth’s surface but one end may dip downward explain
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)
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
Down
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
F is always perpendicular to both B and length. B and length can be at any angle with respect to each other.
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
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).
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
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.
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
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.
Can you set a resting electron into motion with a steady magnetic field, with an electric field
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.
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
The particle will move in a helical path in the direction electrons of the electric field
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
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.
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
No, a charged particle may be deflected sideway by an electric field if a component of its velocity is perpendicular to field.
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
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.
What dos the field do when there is a constant magnetic field acting on a charged particle
Field accelerates the particle
A beam of protons is `
Current
What is speed of lgiht and can anything go faster than that
10^8 and no
A current in a long straight wire produces a magnetic field and these magnetic field lines
Form circles which go around the circle
Consider two long straight parallel wires each carrying a current I if hte currents are flowing in opposite directions
The two wires repel each other
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
Out of hte page
Geophysicists today generally attribute the existence of the earths magnetic field to
Convection currentns with liquid interior
Magnetic declination means
Angle between directs to true north and magnetic north
The magnetic field of hte eart is believed responsible for which of teh following
Deflecting of charged cosmic rays
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
To the right
The path of a charge particle moving parallel to a uniform magnetic field will be whcih of the following
Straight line
The magnetic domains in a nonmagnetized piece of iron are characterized by whcih orientations
Random
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
90 degrees
The force exerted on a current carrying wire located in an external magnetic field is directly proportional ot which of the following
Current strength and field strength
The direction of the force on a current carrying wire located in an external magnetic field is
Perpendicular ot the field and current
A 2 m wire segment caring a current of .6 A oriented parallel to a uniform magnetic field of .5 T experiences what froce `
Zero
A certain charge radiates na electric field a force will be exerted on it when it
Travels in a path normal to a magnetic field
A positive charge Entersa magnetic field and travels parallel to but opposite the field the charge feels or experiences
No force because moving parallel and you need a velocity that is perpendicular or no force
The ratio of an alpha particle to taht of a proton is
2 alpha particle : 1 proton
A charged particle can move through a mnagetic field without a force only when it is
Parallel
Can teh kinetic energy of a charged particle be increased by a magetnci force
NO
How do the magnetic field lines de to current carrying wires radiate from teh wire
In circles around the wire
As the length of a current carrying wire within a uniform magnetic field doubles teh force on teh wire
Doubles
The magnetic field due to current in wires in tour home can affect a compass. Are current ac ro dc adn their distance away
Dc will affect teh compass by teh ac will not
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
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.
Two insulated long wires caring equal currents I cross at fifth angles to each otehr. Describe magnetic force one exerts on tehother
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
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
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
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
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
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
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
biot savards law
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.
Is B teh same for all points in a plane
No B varies in strength due to teh distance, it is the strongest in teh center of teh loop
Why does twistin gthe lead in wires to electrical devices reduce the magnetic effects of teh leads
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.
Compare biot savarts law with coulumbs law
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.
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
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.
Will a magnet attract any metallic object such as aluminum or only those made of iron and why
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.
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
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.
Can an iron rod attract a magnet can a magnet attract an iron rod what msust you consider to answer
Yes, third law applies. Forces are equal and opposite on two different objects.
Why will either pole of a magnet attract an unmagnetized piece of iron
It aligns the domains in the magnet. The N and S pole are equal in strength.
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
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.
Two iron bars attract each toher no mattter which ends are paced close togetehr are both magnets
NO one is a a magnet and the other isnt
Whcih of teh following will a produce a magnetic field
A magnet, teh eart adn moving electric curve add an electric current
When charged particles mvoe parallel to teh direction of a magnetic field the particle travels in a
straight lune becuase it is parallle so no toque
As a proton moves through space it creates
Both an electric and magnetic field
Can a magnetic force be exerted only if the particle is mvoing
True
Does the magnetic field of a current carrying wire exist only if the current in teh wire is changing
No
For a charged particle a constant magnetic field cna be used to change
Only the direction of teh particles velocity
A wire carries a current directly away from your hcih way do teh magnetic field lines produced by w=this wire point
They make circles around the wire
A proton eneters a uniform magnetic field that is perpendicular to teh patrons velocity what happens to teh kinetic energy of teh proton
It stays teh same becuase the centripetal froce acan only change when Toby changing teh direction noteh velocity
The magnetic field depends on
Particle charg particles velocity and strength of teh external magnetic field
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
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
