chapter 21: magnetism

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Chapter 21: Magnetism



What is a magnet?

1.A magnet is anything that carries a static magnetic field around with it..

2.A magnet has a North and South pole.

3.Magnetic lines of flux make up the magnetic field and travel from North to South outside of the magnet.

4.This magnetic field is responsible for the force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.



Describe a permanent magnet.

•Permanent Magnets are the most common type of magnets . These magnets are permanent in the sense that once they have been magnetized they retain a certain degree of magnetism. •Permanent magnets are generally made of ferromagnetic material. Such material consists of atoms and molecules that each have a magnetic field and are positioned to reinforce each other.

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The four types of permanent magnets are:

1. Neodymium Iron Boron (NdFeB or NIB)

strongest types. From the rare earth or Lanthanide

series of elements .

2. Samarium Cobalt (SmCo)

weak and affected by temperature.

3. Alnico

weak and can easily become demagnetized.

Least affected by temperature.

4. Ceramic or Ferrite

Most popular, strength varies greatly with Temp

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Explain why some materials are magnetic and some are not.

1.It's all about unpaired electrons.

2.The transition metals add electrons to the second shell in, so there is the possibility of them being unpaired. Hence Fe Co and Ni.

3.The other Ferro magnets are the rare earths, which likewise are filling the second rather than the outer shell.

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Draw the magnetic field of a Bar Magnet

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How are magnets similar to charges? How are they different? (C1)1. Similar in the following ways:

a. In charges positive (+) and negative (−) electrical charges attract each other.

b. In magnets, the N and S poles attract each other.c. In electricity, like charges repel

d. In magnetism like poles repel.



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2. Different in the following ways:a. The magnetic field must have two poles (N and S).b. A positive (+) or negative (−) electrical charge can stand

alone.

How can you determine the polarity of a magnet? (C2)

1.Polarity identifies a magnets North and South Pole.

2.The North Pole is attracted to the Earth’s geographic North Pole and the south pole of the magnet is attracted to the earth’s geographic South Pole.



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3. Unknown magnet Polarity :a. Suspend the magnet by a thread.b. The North Pole of the magnet will point towards

the geographic North Pole.c. A known polarity magnet brought near the

suspended magnet will attract the opposite pole and repel the like pole.

- Like poles repel (N-N, S-S)- Unlike poles attract (N-S, S-N)



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Determine the polarity of the Earth and compare the poles to the geographical poles.

WARNING WARNING WARNING

1.The geographic north pole is the magnetic south pole.2.The geographic south pole is the magnetic north pole.



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What are magnetic domains? What does the magnetic domain depend on? (C3)

1.Magnetic substances like iron, cobalt, and nickel are composed of small areas where the groups of atoms are aligned like the poles of a magnet. These regions are called domains. 2.All of the domains of a magnetic substance tend to align themselves in the same direction when placed in a magnetic field.

3.The magnetic domain depends on the type of material. Ferromagnetic materials form large magnetic domains.

4.



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The Domain Theory

States that the atoms have their magnetic field lines line up forming atomic magnets called dipoles. The alignment of groups of atomic magnets (dipoles) form domains. It is these aligned domains that then form a bar magnet.



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What is the magnetic field?(C4)

1.A magnetic field consists of imaginary lines of flux coming from moving electrically charged particles. (Ex. Electric current)

2.A charge moving through this magnetic field experiences a force. Calculated by F= Bqv3.The SI unit for magnetic field (B) is the Tesla (T). 1T=N/(Cm/s).



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4. Magnitude of a magnetic field (B) is calculated using:

B = Fmagnetic /qv

•Fmagnetic = magnetic force on a charged particle (N)

•q = magnitude of charge (c)

•v = speed of charge (m/s)



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Magnetic Field of a current carrying conductor.(Right Hand Rule)



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How can magnetic field lines be used to find the poles of a magnet? (C5)

1.Magnetic field lines travel from North to South Poles outside of the magnet.2.A compass reveals that magnetic field lines outside of a magnet point from the north pole (compass points away from north pole) to the south (compass points toward the south pole).



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How do we know that the Earth is a giant magnet?(C6)

1.The compass was used to discover that the Earth is a huge magnet. The North-seeking pole of the compass needle will always point toward the Earth's North magnetic pole.



Give two examples of the effect of Earth’s magnetic field.

•Deflects the needle of a compass.•Interferes with AM radio •Northern lights

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How is the Right Hand Rule used to figure out the direction of force, field, and current? (C7)

1. Hold your right hand as if you were going to shake someone's hand. The thumb forms a right angle with the index finger.

Thumb- Direction of current flow (+ to -)

Fingers- Direction of magnetic field

Palm- Direction of force



Right Hand Rule



FLEMMINGS RIGHT HAND RULE

• Also known as the Generator Rule this is a way of determining the direction of the induced emf of a conductor moving in a magnetic field. The thumb, the first and the second fingers on the right hand are held so that they are at right angles to each other. If the first finger points in the direction of the magnetic field and the thumb in the direction of the motion of the conductor then the second finger will point in the direction of the induced emf in the conductor.



FLEMMINGS LEFT HAND RULE

• Also known as the Motor Rule this is a way of determining the direction of a force on a current carrying conductor in a magnetic field. The thumb, the first and the second fingers on the left hand are held so that they are at right angles to each other. If the first finger points in the direction of the magnetic field and the second finger the direction of the current in the wire, then the thumb will point in the direction of the force on the conductor.



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What is the difference between the Right Hand Rule and the Left Hand Rule? (C8)

1.The right hand rule is used to determine the direction of induced current when a conductor is moved through a magnetic field. 2.The left hand rule is used to determine the direction of the force (motion) on a current carrying conductor in a magnetic field.



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How are the magnetic fields and electric fields related? (C9)

1.Electric fields result from the strength of the charge while magnetic fields result from the motion of the charge, or the current.

2.A changing magnetic field creates electrical current---an electric field.

3.The magnetic field will be perpendicular to the electric field and vice versa.



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What conditions are necessary for a current to be induced in a wire? (10)

1.The wire must be a current carrying conductor connected into an electric circuit.

2.The wire must move through a magnetic field or the field must move through the stationary conductor.

3.This is called electromagnetic induction.



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Electromagnetic Induction in a Circuit Loop

Section 1 Electricity from Magnetism



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What is an electromagnet and how is it made? (C11)

1.An electromagnet is a magnet that runs on electricity. a. Strength depends on the amount of electric current.b. The poles can be reversed by reversing the current flow.

2.One can be made by:a.Wrapping insulated copper wire around an iron core.

b.Attach a battery to the wire.

c.Current will begin to flow and the iron core will become magnetized.

d.When the battery is disconnected, the iron core will lose its magnetism.



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What is Lenz’s Law and how does it relate to Faraday’s Law? (C12)

1.Lenz’s law -The magnetic field of the induced current is in a direction to produce a field that opposes the change causing it.



2. Lenz’s law allows you to determine the direction of an 2. Lenz’s law allows you to determine the direction of an induced current in a circuit.induced current in a circuit.

3. 3. Faraday’s law- Faraday’s law- The emf (Voltage) generated through The emf (Voltage) generated through magnetic induction is proportional to the rate of magnetic induction is proportional to the rate of change of the magnetic flux.change of the magnetic flux.

*the (-) in front of N comes from Lenz’s law*the (-) in front of N comes from Lenz’s law



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What is the electromotive force (emf)? (13)

1.When a voltage is generated by a battery, or by the magnetic force according to Faraday's Law, this generated voltage has been traditionally called an "electromotive force" or emf.

2.The emf represents energy per unit charge (voltage) which has been made available by the generating mechanism and is not a "force".

3.Emf is voltage



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What is an electric motor and how does it work?(C14)

1.Rotating coils of wire with current flow are driven by the magnetic force exerted by a magnetic field on an electric current.

2.Motors transform electrical energy into mechanical energy through motor action.

3.Motor action- When a current-carrying conductor is located in an external magnetic field the conductor experiences a force due to the interaction between the two fields.



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How is an electric motor similar to a generator? (C15)

1.A generator works by the turning of a coil in a magnetic field which induces voltage (emf) in the coil. Current flows out of the coil to the circuit loads.

2. Generator action- A conductor, a magnetic field and relative motion between them will result in a voltage being induced in the conductor.



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4. Reversing a generator can cause motor action.

5. Reversing a motor can cause generator action.

6. The machines can be converted to motors or generators. Such machines are called motor-generators.



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What is mutual and self-inductance and how do they occur in circuits?(C16)

1.The changing magnetic field created by one circuit (the primary) can induce a changing voltage and/or current in a second circuit (the secondary). (Transformer works this way)2.The mutual inductance, M, of two circuits describes the size of the voltage in the secondary induced by changes in the current of the primary:



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3. Self Inductance- When current changes in a individual circuit the magnetic field caused by the original current flow begins to collapse. This induces an opposing voltage in the circuit.



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What types of radiation are considered part of the electromagnetic spectrum? (C17)

1.Radio waves

2.Microwave

3.Infrared

4.Visible

5.Ultraviolet

6.X-Ray

7.Gamma Rays



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How is electromagnetic radiation related to electromagnetic induction?(C18)1.Electromagnetic radiation is the transfer of energy associated with an electric and magnetic field.

1.Electromagnetic induction is the production of voltage across a conductor moving through a magnetic field.



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How can electromagnetic radiation be categorized in terms of waves? (C19)

•Electromagnetic waves (radiation) are transverse waves; that is, the direction of travel is perpendicular to the direction of oscillating electric and magnetic fields.•Scientists have observed that electromagnetic radiation has a dual "personality." Besides acting like transverse waves, it acts like a stream of particles (called "photons") that have no mass.



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What is the speed of light and what limitations are there to this speed?(C20)1.The speed of light (c) in a vacuum is a physical constant. Its value is 299,792,458 meters per second..

2.This speed is approximately 186,282 miles per second.

3.It is the maximum speed at which all energy, matter, and information in the universe can travel.

4.It is the speed of all massless particles and associated fields—including electromagnetic radiation .



Practical Skills List

• For given situations, predict whether magnets will repel or attract each other.

• Describe the force between two magnetic poles

• Explain magnetism in terms of the domain theory of magnetism.

• Demonstrate knowledge of magnetic fields, their generations, orientation and effect upon charged, moving particles.

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• Explain why some materials are magnetic and some are not.

• Describe four different categories of magnets.

• Describe and draw the magnetic field for a permanent magnet.

• Describe and draw the Earth’s magnetic field.

• Determine the polarity of the Earth and compare the poles to the geographical poles.

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• Give two examples of the effect of Earth’s magnetic field.

• Use the right-hand rule to find the direction of the force on a charge moving through a magnetic field.

• Understand and apply Faraday’s Law to electromagnets

• Determine direction of the force on a wire carrying

current in a magnetic field.

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Practical Skills List• Determine the relationship between magnetic field and

current.

• Understand and apply Lenz’s law to determine the direction of an induced current.

• Explain how a magnetic field can produce an electric current.

• Describe how an electric motor and electric generators work as well as how electromagnetic induction works for devices such as doorbells and galvanometers.

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Practical Skills List• Describe how mutual inductance occurs in circuits.

• Describe how self-inductance occurs in an electric circuit.

• Explain why electromagnetic waves are transverse waves.

• Describe how electromagnetic waves are produced.

• Identify how EM waves differ from each other.

• Identify the components of the electromagnetic spectrum.

• Describe some uses for radio waves and microwaves.

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Practical Skills List• Give examples of how infrared waves and visible light are

important in your life.

• Explain how ultraviolet light, X rays, and gamma rays can be both helpful and harmful.

• Calculate the frequency or wavelength of electromagnetic radiation.

• Recognize that light has a finite speed.

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chapter 21: magnetism

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