Magnetism and Electrodynamics Flashcards

MAGNETISM AND ELECTRODYNAMICS

• Magnetism is an important part of daily life, used for various applications like posting notes and navigation.
• Magnetism and electricity are related through change and motion, with moving charges giving rise to magnetism and changing magnetism giving rise to electricity.
• The field of physics that covers these relationships is known as electrodynamics, with most magnetism being electromagnetism.

Experiment: Building a Simple Electromagnet

• Materials needed: large steel nail/bolt, insulated wire (at least 0.65 mm diameter), a 1.5-volt AA battery, and small steel objects (e.g., paper clips).
• Procedure: Wind the wire tightly around the nail/bolt to form a coil with at least 50 turns in the same direction. Remove insulation from both ends to connect to the battery.
• Testing: Connect the uninsulated ends of the coil to the battery terminals. Be prepared for the wire to get hot. Use a AA battery or smaller to avoid dangerous heat.
• Observation: The nail acts as a strong electromagnet, temporarily magnetizing steel objects it touches.
• Questions: What happens when touching a magnetized steel object to another object? What happens when stopping current flow? Why does the coil get hot?

Chapter Itinerary

• Household Magnets: Examining forces that bind magnets, compass direction, and electric doorbells.
• Electric Power Distribution: How electricity and magnetism transport power from power plants to homes and differences between battery and electric power.

Household Magnets

• Magnets are useful and allow experimenting with basic forces in nature.
• Magnetism is related to electricity, eventually unifying into a single whole.
• Focus on treating magnetism separately before integrating electricity.

Questions to Consider

• Why do magnets attract or repel based on orientation?
• Why don't refrigerators attract each other if a magnet sticks to them?
• How can magnets grip through a hand without involving the hand?
• How can electricity turn magnets on/off?

Experiments to Do

• Use button-type refrigerator magnets to observe attraction/repulsion based on orientation and separation.
• Test floating one magnet on top of the other using repulsive forces.
• Observe the interaction of a button magnet near a refrigerator or steel object.
• Try to make two objects repel. Test if magnets stick to non-steel materials (e.g., stainless steel).
• Use sheet-type magnets and experiment by sliding them. Observe attraction and repulsion patterns.
• Sprinkle iron powder on magnets and note strand formations bridging gaps. Check if powder bridges form on credit cards or magnetic ID cards.

Button-Shaped Refrigerator Magnets

• Forces between magnets can be attractive or repulsive and weaken with distance.
• Magnetic forces resemble electric ones (e.g., static cling) but have differences.
• Reorienting charged garments changes attraction/repulsion; magnetic sparks don't jump between magnets like electric sparks.
• Magnetism resembles electricity: two types of magnetic poles (north and south) exert magnetostatic forces.
• Poles are magnetic, charges are electric, with north and south being exact opposites.
• North poles carry positive magnetic pole amounts; south poles carry negative amounts.
• Like poles repel; opposite poles attract. Magnetostatic forces weaken with distance, inversely proportional to the square of the distance.
• Subatomic particles with pure charges are common, but pure magnetic poles (monopoles) haven't been found and may not exist.
• No magnetic sparks occur without monopoles due to no equivalent of electric charge leaps.
• Pairs of magnetic poles exist: magnetic dipoles with equal north and south poles separated spatially, summing to zero net magnetic pole.
• Button magnets have north and south poles on opposite faces with zero net pole.
• Slicing a button magnet creates new poles at cut edges with each piece having zero net pole.
• Interactions: considering repulsive (north-north, south-south) and attractive (north-south) interactions.
• Distances between poles determine force strength, with closest poles dominating.
• Like poles facing each other cause repulsion; opposite poles cause attraction.
• Angled magnets experience torques twisting opposite poles together and like poles apart.

Units and Coulomb's Law

• SI unit of magnetic pole: ampere-meter (A·m), foreshadowing electricity and magnetism connections.
• Coulomb's law for magnetic poles defines forces' proportionality to pole amounts and inverse proportionality to separation squared.
• Word equation: force = permeability of free space * pole1 * pole2 / (4π * (distance between poles)^2)
• Symbolic equation: F = frac{μ0 * p1 * p_2}{4πr^2}
• Permeability of free space: μ_0 = 4π × 10^{-7} N/A^2
• Force on pole1 is directed toward/away from pole2; force on pole2 is directed toward/away from pole1.
• Consistent with Newton’s third law, forces are equal in magnitude and opposite in direction.

Coulomb's Law for Magnetism

• The magnitudes of the magnetostatic forces between two magnetic poles are equal to the permeability of free space times the product of the two poles divided by 4π times the square of the distance separating them.
• If the poles are like, then the forces are repulsive. If the poles are opposite, then the forces are attractive.

Check Your Understanding #1

• Cracked magnets oppose reassembly due to potential energy within.
• Made of tiny magnets, aligned with like poles together that repel each other.
• Strong magnets release potential energy when cracked, behaving explosively.

The Refrigerator: Iron and Steel

• Magnets attract refrigerators/steel; flipping the magnet won't cause repulsion.
• Steel contains microscopic magnets with north/south poles oriented randomly.
• Bringing a magnet near causes tiny magnets to evolve in size, shape, and orientation; opposite poles shift closer to button magnet's pole, like poles shift farther.
• Steel develops magnetic polarization, attracting the button magnet's pole.
• Polarization weakens when the magnet is removed; tiny magnets resume semi-random orientations.
• Bringing the button magnet's other pole near causes the steel to develop the opposite magnetic polarization.
• Plastic/aluminum surfaces don't allow magnets to stick.

Ferromagnetism

• Ordinary steel (ferromagnetic) is magnetic on an atomic scale.
• Subatomic particles (electrons, protons, neutrons) have magnetic dipoles, especially electrons.
• Atoms formed often display magnetism; subatomic particles pair with opposite orientations to cancel magnetic dipoles.
• Most isolated atoms possess significant magnetic dipoles, but most materials aren't magnetic due to pairing/cancellation during assembly.
• Materials like glass, plastic, skin, copper, and aluminum lack atomic-scale magnetism. Most stainless steels are nonmagnetic.
• Ferromagnets (ordinary steel, iron) avoid total cancellation, remaining magnetic at the atomic scale.
• Ferromagnetic steel comprises microscopic regions or magnetic domains that are naturally magnetic and cannot be demagnetized.
• All atomic-scale magnetic dipoles are aligned within a single domain, giving domains a substantial net magnetic dipole.
• Nearby domains in common steel are oriented to oppose and cancel each other, making the steel appear nonmagnetic.
• Bringing a strong magnetic pole near steel causes individual domains to grow/shrink depending on orientation.
• Steel undergoes magnetization as its atoms' magnetic dipoles reorient; domains attracting the pole grow, while repelling ones shrink.

Check Your Understanding #2

• Touching the north pole of a magnet to a paper clip's end makes the other end magnetic with a north pole.
• The paper clip polarizes magnetically, with its south pole nearest the permanent magnet’s north pole. The other end of the paper clip will have a north pole and will be able to polarize other paper clips.
• Polarized clips attract and cling together to form a chain.

Plastic Sheet Magnets and Credit Cards

• Steel returns to a nonmagnetic state after the button magnet is removed through demagnetization.
• Residual magnetism remains because some domains get stuck due to chemical forces that make it difficult for domains to grow/shrink.
• Domain walls exist between magnetic orientations, and flaws/impurities interact with domain walls, preventing movement.
• Heat or mechanical shock must be applied to help domain walls move and remove residual magnetism.
• Soft magnetic materials easily demagnetize (e.g., chemically pure iron).
• Hard magnetic materials resist demagnetization and retain domain structure (e.g., button magnets).
• Button magnets were magnetized during manufacturing for permanent magnetic poles and retain magnetization unless exposed to strong magnetic influences, heat, or pounding.
• Plastic sheet magnets have multiple poles with alternating patterns (stripes).
• Attraction and repulsion occur based on alignment; strongest attraction when opposite poles align and repulsion when like poles align.
• Hard magnetic materials store information, retaining magnetization until magnetized differently; information retention forms the basis for magnetic recording and storage in credit cards, tapes, disks, and MRAM.

Check Your Understanding #3

• Bringing a strong magnet's north pole near a small magnet's north pole will cause the poles to interchange.
• The small magnet's poles switch when repulsion becomes strong enough, presenting its south pole to the large magnet's north pole, reversing its poles permanently.

Compasses

• Compass needles are simple permanent magnets with north/south poles.
• Needles aid navigation due to Earth's magnetic dipole, with the north pole tending to point northward.
• Earth has a south magnetic pole near its north geographic pole.
• Full story more complex; magnetic poles located beneath surface and not perfectly aligned with geographic poles along with magnetic materials influencing the needle.
• Compass needle responds to countless magnetic poles, and is easier to view interacting with a local magnetic field.
• Magnetic field is an attribute of space exerting magnetostatic force.
• Magnetic fields are real, existing independently of poles, and created by things other than pole.
• Magnetic field measures the magnetostatic force a unit north pole experiences.
• Equation: magnetostatic force = pole * magnetic field.
• Symbolic Equation : F = pB
• Direction of magnetostatic force : In the direction of the magnetic field.
• SI unit of magnetic field: tesla (T), equivalent to newton per ampere-meter.
• Earth's magnetic field is weak, pushing the compass needle's north pole northward and south pole southward.
• The needle rotates horizontally and settles with its to minimize magnetostatic potential energy and achieve stable equilibrium. Points along the local magnetic field that points northward.
• Uniform Earth's magnetic field results in zero net force on the needle due to balanced pushes but bringing a button magnet nearby will cause a net force.
• The needles experiences a net force towards or away from a pole. If aligned against the field, it experiences a net force toward decreasing field. The needle aligns with the button magnet and then finds itself pulled to the nearest pole.
• Steel exhibits similar behavior: becoming magnetized, then moves toward the magnet's nearest pole.

Check Your Understanding #4

• Locking the compass needle and moving its north pole near a strong magnet's north pole causes a force toward weak field.
• The compass needle, when aligned opposite the button's field, is forced from the button magnet.
• Continued pushing can reverse poles permanently to point south rather than north, but can be restored by repeating the procedure.

Check Your Figures #1

• A long steel wrench mistakenly placed in a 1-T field near a magnet magnetizes and develops a 1000 A·m north pole at the near end and equal south pole at the distant end.
• The 1-T field exerts a force on the wrench with north pole : 1000 N.
• Force Exerted F = 1000 A.m *1 T= 1000N in the direction of the field.

Iron Filings and Magnetic Flux Lines

• Sprinkling iron filings in a field reveals magnetic fields: particles magnetize along the field and stick together, mapping flux lines.
• Strands point along the local magnetic field and pack tightly where the field is strongest. These lines are magnetic flux lines.
• Walking with a compass maps flux lines; lines lead from north poles to south poles, either one of the two.
• Flux lines don't start/end in empty space. Flux line you're following doesn't end at a pole is because such fields are produced by electricity.

Check Your Understanding #5

• Iron filings sprinkled on a credit card's magnetic strip form bridges as tiny iron bridges; the poles are at the ends of the bridges.
• The iron filings follow the lines to extend from north poles to south poles.

Electric Doorbells and Electromagnets

• Door bell circuit operation described with magnet and spring to strike a chime.
• Electric currents can produce magnetic forces.

The First Connection Between Electricity and Magnetism

• Moving electric charge produces a magnetic field, and the induced electromotive force is created.
• Oersted observed current in a wire causing a compass needle to rotate in 1820: showed connection between electricity and magnetism.
• Ampère studied relationships between electricity and magnetism further, unifying them.
• Iron powder discloses flux lines surrounding a current-carrying wire; concentric rings grow more widely separated with increasing distance from the wire.
• Wire is an electromagnet with no true magnetic poles where the flux lines can’t stretch from North pole to South pole.Each flux line of an electromagnet is a closed loop.
• Magnetic field is strongest near the wire's surface, attracting iron.
• Practical doorbells wind wire into coil to strengthen field winding.
• Remarkably, the flux lines outside the coil resemble those outside a button magnet of similar dimensions. The coil appears to have a north pole at one end and a south pole at the other.
• Flux don't end, they continue straight through the middle of the coil like loops.
  When current is fl owing iron is pulled inward towards the center of the coil as the result of tightly packed flux lines at he end of the coil.
• Pressing the doorbell button make the coil yank an iron rod to the center of the coil to strike a chime.
• The magnetic surrounding the coil are the sum of modest magnetic from the coil and strong magnetic from the rod.

Check Your Understanding #6

• Magnetic Resonance Imaging (MRI) uses intense magnetic field without magnets but with Current in a coil
• MRI requires intense uniform spacious field that can fit patients with the best way created by using a Current - carrying coil which has strong flux which can be dangerous

Electric Power Distribution

• Electricity is useful being delivered to homes and offers convenience.
• Problems are caused during the distribution of electricity and understand affect of way of wires while devices like transformers are being transfered.

Questions to Think About

• -Why do power distribution systems use alternating current?
• -What is the purpose of high-voltage wires?
• -Why does the power company place large electric devices on the utility poles near homes or on the ground near neighborhoods?
• -What are the advantages and disadvantages of 120-V versus 230-V electric power?

Experiments to Do

• -Experiments with electric distribution can be dangerous but observation is possible
• -Facilities include a hierarchy of power conversion with different power levels being taken in to consideration
• -Power travels major electric networks through hi voltage overhead and then to to power conversion facilities to lower voltage. However that power still needs to be ready for household use it is being through at lest one more stage conversion where transformers are used in the conversion process

WARNING

Electricity is dangerous, High voltages are dangerous circuits have a tendency to form surprising ways when you touch an electric wire. Especially when near over 50V or if your skin is broken and wet, Voltage of 12 volts is too less and rare cases for the chance of shock and batteries provide safety and can be handle individually with little shock.

Direct Current Power Distribution

• Batteries are inefficient and batteries are not well suited for for homes with short lives span needing fresh chemicals.
• Generators are an alternative to batteries with ability to light homes with electric generations with the use of coal or oil power.
• Generator use began with placing generators to central area with chimneys to get rid of smoke used by Thomas Edison.
• Wires impeded flows which are thick copper which is important because wires has electrical resistance which increases the the voltages drop through generators.
• Power Consume expression is given which are proportional to the square of current passing.
• Power consumed = Voltage x Current
• Edison Combats Power loss by Lowering Electric Resistance use copters and short wires as well has small currents at high voltages. However high voltages is dangerous which causes sparks.
• Superconductors are used which lose electrical resistance at extremely low temperature is impractical for power distribution.

Check Your Understanding #1

• If the length of wires are doubled its power consumed get doubled which is proportional to the length of wire and inversely to the electrical resistance to the cross sectional areas.

Introducing Alternating Current

*DC has not easy way to transfer power from one DC system to the next which DC distributions power has major waste that wastes power due to wires which connect. AC provides power from one AC circuits which allos the system to have different ranges of voltages with low voltages.
*AC an alternating current that reverses direction where you have the power supply propel the alternating direction. The battery subjects to filliment to steady voltages gradients
AC alternating voltages are present at any AC electrical outlet that are three main connection : hot neutral and ground. Where Neutral has voltage of 0V and hot alternating both both 0V and Ground 0V.

• Hot to neutral with positive volts and neutral to hot with native voltages in with flows. Volts reverse at 120th yielding to 60 cycle per second (60 HZ) And Voltage reverse it self 100TH cycle per second.
  Most household do not care which why the current flow. But reverses have consequence. Electrical are sentives o the directions

The nominal AC. Voltage:

• The power consumption is the same average for 120V DC Power and 120 AC Power
• The reverses voltage values exceed about 1.414 of values which is important to electrical safety

Check your understanding #2:

*It never a good idea to stick your finger in. But briefly when voltage reaching V you will not get shocked. To avoid but it not realistically safe in the electric cord.

Magnetic Induction

*Edisons opposed AC voltage calling them a dangerous and exotic. Tesla Champion AC voltage making its power that can be transformed. From on of its kind.
*A transformer uses two connection from electricity and magnetism to convey power from one. Electricity to produce magnetic and magnetic field produces electricity.
Magnetic induction change in time in field initiates or influence electric current.

Electric Conductor

• Second Connection between Electricity and Magnetism: Magnetic fields that change with time produce electric fields.
  Whether you wave a permanent magnet back and forth, or switch an electromagnet on and off, you are changing a magnetic field with time and thereby producing an electric field.

Check your understanding#3:

*The Phonograph reproduces sound from the grooved record using stylus with magnet the moves the magnet near the coil and produces it creating a induced electromotive force in the coil. The moving magnet affected the coil by producing field to push moving charged to wire coil

Alternating Current and a Coil of Wire

What happen when you send the alternating current through a single wire since currents is magnetic the coil acts as electromagnetic since it reverses magnetic field it also produces an electric field.

Which has a remarkable effect is that push on alternatina current that produce in. When coil increases is the induced elds pushes back to not reduce increase as it

• Lenz's law: is when changing magnetic field induces a current where current is changed opposing the change. Coil opposes it and called inductor.

Increasing current: produces magnetic current and current is produced and decreased

• Decrease in current in coil of the resulting emf now opposed the emf.

Lenz’s Law:

• When a changing magnetic field induces a current in a conductor, the magnetic field from that current opposes the change that induced it.
  However, magnetic induction does more than just push currents around it transfers energy. With induced fields does for charge who move and negative work where push that goes into coil that is induced increases where coil start finished is cause induced electromotive

Induced Emf has negative and positive swing and is in the energy in the is coilds magnetic fields.

• Electric field = magnetism^ 2 * field/ (2 * μ_0)
• Strong permsnents magnets can be dangerous with pieces flipping since it it has a lot of energy .which they brief play in the magnetic coil which alterantes and which increase the curret. Where coil responsible is caused induced for to back emfs. Coild does an affect to AC without trpoubles.

Check your understanding 4

*If Magnet slowly falls to non mgnaetc sureface, it causes Magnet to indues and currenst for it to flow where it slows down magnet.

Checky ur figure 1

*The MRI field is 0.01 meters cubed wit with field of tesla =6400 joules

Two Coil Together: tranmsfomer

• *There coils for it to trnasfer. The the current to go on.
  In the two coils which they share where their are seperate envionrment with can be with drawm. The coils never touching and they are the basis to tramsforsmion.

Secondary Coiel

*That coil forms with the lamp fillemtns where it passes to the filaments where has the effect and electric with the primary that induces and emf. That removes currents
*Transfer is automated and the power that transfer current primary to section . The perfect transformer not really the transformer that all consume.

Check your understanding 5:

• AC does what the coil need to not to keep constant the coil so that will not induced it but AC is on with which make the circuit to make those type of coil.

ChangingVoltages:

• Its the lamp needs volts where has small volts or power that are big because resistance has to be thick an short compare to the others , where power is a major issue with the wire and small for the electric resistance.
  where each are increase from. It can cause high electric charge transfer to small and so one , for where it becomes 1.

  SecondVoltage= second turns

• ––––––––––––––––*

PrimaryVoltage= Primery Runs

Step Down Transformer

• With the help of a big ac, for to have as the many of volts runs like a isolation where both run 120 c with and electricity.

Check your understanding #6.

*Your Travel power has to be half to 240 to to 120 where transforemr is half in the primary and seconder . It to reduce the EMF.

Real Transforming: Not Quiet Perfect.

*That Tranformers flaless and the thst wire work pefectly because real wires it has eletirtical . which has powers is wire and made if miniziation for it has ressitence. THTE TRANSFORMORS HAVE HAS TO MAny ruis so they work. Small transormer hawe core that allows the. It make with shoring that that coils and is not easy is to share what goes one. However these flx for a lot
tranfsomers has great for the coils and where that can has leak that. That the coils work and coil can and need a littke more because .It can. be lost or. it couel be in conductivity which needs to be cool

Check Your Undestand :winds Of change Large power transfomes have Coolding which cause transfomes convert the power. INto power.

Alternating Current Power Distribution . . . the Power can now. Minimixe the power transfer. The transmforsm make and eassd for an DC system use with the elcticit.

That goes up for 5 k volts with current 1 /100 . The transfomer that goes to the power plants
High that needs to reduce as the the resitance increases
Then the current passes too one of the coils where its low as the next

Check You Understandig 8

• Hgh Voltsge wires has increases. By an large 1kk million will will reduce the heat from heat that use only 25
  AC Electric Generators and Motors ….
  Trafoemrs convert powers from electis to electric poweer wehre mechanical ower and electicl poweer are physcially , wha happwen replace one the electrical. With ac mechsnism ? which gives the generator

Ac electical Motor And generator: ac looks that has power with spinning ac alternting fiele, where EMF alters its , for coil to have interact

For rotor is that machine must the genor is the rotor. And alterante which power so it cna have it .
This power also come that transfromer ha thsi coils and give with cricus. That it suppolyeis.
THYE are reasoble cirl

Check you understanding elctirtic with biking

Epilogue for chapter 11

This chapter, we studied magnetism and the ways in which magnetism relates to electricity. In Household Magnets, we looked at the concept of magnetic pole and the attractive or repulsive forces that poles exert on one another. We examined magnetic materials and saw how their magnetic properties make them useful for various purposes. We also encountered electromagnets and began to see that magnetism isn’t independent of electricity. In Electric Power Distribution, we saw how alternating electric currents make it possible to transfer power from one circuit to another by way of a transformer and its electromagnetic properties. We learned that transforming electric power to extremely high voltages and small currents minimizes the power wasted between power plants and cities.

Important Laws and Equations

Explanation: A Nail and Wire ElectromagnetWhen you connect the wire from one terminal of the battery to the other, a current flows from the positive terminal to the negative terminal through the wire. (In reality, negatively charged electrons move from the battery’s negative terminal, through the wire, to its positive terminal, but we’ve adopted a fiction that positive charges are heading the other way.) This current produces a magnetic field around the wire. Because the wire is coiled around the nail, this magnetic field passes through the nail and causes its magnetic domains to resize until most of them are aligned with the field. Without any current in the wire, the magnetic domains in the steel point in many different directions, so the nail appears nonmagnetic. However, with the current orienting the domains, they together produce a large magnetization. The nail becomes magnetic and exerts strong magnetic forces on other nearby objects.

Chapter Summary

• How Household Magnets Work: Common refrigerator magnets are composed of hard magnetic materials that were permanently magnetized by their manufacturers. Simple button magnets have a single pair of magnetic poles, one north and one south, but plastic sheet magnets usually have many poles. These magnets stick to a refrigerator’s surface by temporarily magnetizing that surface’s soft magnetic materials and then becoming attracted to the opposite poles on that surface.
• A compass is another permanent magnet, but one designed to align with Earth’s magnetic field. In fact, that magnetic field can be mapped out using a compass. The magnetic fields around smaller magnets can be made visible with iron filings instead. However, permanent magnets aren’t the only sources of magnetic fields; we found that when current flows through the coil in a doorbell, it becomes a magnet as well—an electromagnet.
• How Electric Power Distribution Works: To minimize power losses in the transmission lines between power plants and cities, power distribution systems use alternating currents and transformers. Near the power plant, relatively low-voltage, high-current electric power is transformed into very-high-voltage, low-current power for transmission through cross-country power lines. Because the power consumed by these high-voltage wires depends on the square of the currents they carry, the power losses are greatly reduced by this technique. When the power arrives at a city, it’s transformed into medium-voltage, high-current power for distribution to neighborhoods. Finally, in neighborhoods, step-down transformers transform this power to low-voltage, very-high-current power for distribution to individual homes and offices.

Important Laws and Equations

1. Coulomb’s law for magnetism: The magnitudes of the magnetostatic forces between two magnetic poles are equal to the permeability of free space times the product of the two magnetic poles divided by 4π times the square of the distance separating them, or force = frac{permeability \,of \,free\, space * pole1 * pole2}{4π * (distance \, between\, poles)^2}. If the charges are like, then the forces are repulsive. If the charges are opposite, then the forces are attractive.
2. Force exerted on a pole by a magnetic field: A pole experiences a force equal to its pole times the magnetic field, or magnetostatic force = pole * magnetic field, where the force points in the direction of the field.
3. Lenz’s law: When a changing magnetic field induces a current in a conductor, the magnetic field from that current opposes the change that induced it.
4. Power consumed by a wire or other ohmic device: power consumed = current^2 x electrical resistance.
5. Energy in a magnetic field: The energy in a magnetic field is equal to the square of that field times its volume, divided by twice the permeability of free space, or energy = (magnetic field^2 * volume) / (2 * permeability of free space).
6. Transformer voltages: A transformer’s secondary coil acts as a source of AC power with a voltage equal to the AC voltage applied to its primary coil times the ratio of secondary turns to primary turns or secondary voltage = primary voltage * (secondary turns / primary turns).
7. Transformer currents: The AC current in a transformer’s secondary coil is equal to the AC current in its primary coil times the ratio of primary turns to secondary turns or secondary current = primary current * (primary turns / secondary turns).

Exercises

1. Is it possible to have two permanent magnets that always attract one another, regardless of their relative orientations? Explain.
2. The magnetostatic forces between two button magnets decrease surprisingly quickly as their separation increases. Use Coulomb’s law for magnetism and the dipole character of each button magnet to explain this effect.
3. If you bring two magnetic compasses near to each other, they will soon begin attracting one another. Why don’t they repel each other?
4. If you bring a button magnet near an iron pipe, they will soon begin attracting one another. Why don’t they repel one another?
5. If you hold a permanent magnet the wrong way in an extremely strong magnetic field, its magnetization will be permanently reversed. What happens to the magnetic domains inside the permanent magnet during this process?
6. Hammering or heating a permanent magnet can demagnetize it. What happens to the magnetic domains inside it during these processes?
7. If you place a button magnet in a uniform magnetic field, what is the net force on that button magnet?
8. If you hold a magnetic compass in a uniform magnetic field pointing northward, in which direction, if any, is the net magnetic force on the compass?
9. Do more magnetic flux lines begin or end on a button magnet, or are those numbers equal?
10. Compare the number of magnetic flux lines beginning and ending on a plastic strip magnet. Explain.
11. Two plastic strip magnets differ only in how many poles they have per centimeter: one has 2 poles/cm and the other has 4 poles/cm. From which strip’s surface do magnetic flux lines extend outward farther?
12. Which of the two plastic strip magnets in Exercise 11 is attracted toward a refrigerator at the greater distance?
13. How could you use iron to prevent the magnetic flux lines from a strong button magnet from extending outward into the room?
14. To keep the strong magnets in a scientific facility next door from sending flux lines through your office, should you line the office walls with aluminum or with iron?
15. Your friends are installing a loft in their room and are using thin speaker wires to provide power to an extra outlet. If they draw only a small amount of current from the outlet, the voltage drop in each of the wires will remain small. Why?
16. When your friends from Exercise 15 plug a large home entertainment system into the outlet, it doesn’t work properly because the voltage rise provided by the extra outlet is only 60 V. The power company provides a voltage rise of 120 V, so where is the missing voltage?
17. A particular lightbulb is designed to consume 40 W when operating on a car’s 12-V DC electric power. If you supply that bulb with 12-V AC power from a transformer, how much power will it consume?
18. Your toaster consumes 800 W when operating on 120-V AC electric power. If your rugby team is camping and all of you string together flashlight batteries to supply that toaster with 120-V DC electric power, how much power will it consume?
19. To read the magnetic strip on an ID or credit card, you must swipe it quickly past a tiny coil of wire. Why must the card be moving for the coil system to read it?
20. One type of microphone has a permanent magnet and a coil of wire that move relative to one another in response to sound waves. Why is the current in the coil related to the motion?
21. If the primary coil of a transformer has 200 turns and is supplied with 120-V AC power, how many turns must the secondary coil have to provide 12-V AC power?
22. The transformer supplying power to an artist’s light sculpture provides 9600-V AC when supplied by 120-V AC. If there are 100 turns in the transformer’s primary coil, how many turns are there in its secondary coil?
23. The primary coil of a transformer makes 240 turns around the iron core, and the secondary coil of that transformer makes 80 turns. If the primary voltage is 120-V AC, what is the secondary voltage?
24. The transformer in a stereo amplifier has a primary coil with 200 turns and a secondary coil with 40 turns. When the primary coil is supplied with 120-V AC, what voltage does the secondary coil provide?
25. If an average current of 3 A is passing through the primary coil of the transformer in Exercise 23, what average current is passing through the secondary coil of that transformer?
26. If the average current passing through the secondary coil of the transformer in Exercise 24 is 10 A, what average current is passing through the primary coil?
27. A magnet hanging from a spring bounces in and out of a metal ring. Although it doesn’t touch the ring, the magnet’s bounce diminishes faster than it would if the ring weren’t there. Explain.
28. The high-voltage spark that ignites gasoline in a basic lawn mower engine is produced when a magnetic pole moves suddenly past a stationary coil of wire. From where does that spark’s energy come?
29. Suppose you include an inductor in an electric circuit that includes a battery, a switch, and a lightbulb. Current leaving the battery’s positive terminal must flow through the switch, the inductor, and the lightbulb before returning to the battery’s negative terminal. The current in this circuit increases slowly when you close the switch, and it takes the lightbulb a few seconds to become bright. Why?
30. When you open the switch of the circuit in Exercise 29, a spark appears between its two terminals. As a result, the circuit itself doesn’t open completely for about half a second, during which time the bulb gradually becomes dimmer. The bulb’s behavior indicates that the current in the circuit diminishes slowly rather than stopping abruptly when you open the switch. Why does the current diminish slowly?

Problems

1. If a 0.10-A·m magnetic pole is placed in an upward-pointing 1.0-T magnetic field, what