Physics Ch 11 – Flashcards
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Ph Ch 11 Define magnetic force
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1- Between magnets, it is the attraction of unlike magnetic poles for each other and the repulsion between like magnetic poles 2- between a magnetic field and a moving charge: the deflecting force is perpendicular to the velocity of the charge and perpendicular to the magnetic field lines. This force is greatest when the charge moves perpendicular to the field lines and is smallest (zero) when it moves parallel to the field lines
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Ph Ch 11 Define magnetic field
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the region of magnetic influence around a magnetic pole or a moving charged particle
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Ph Ch 11 Define magnetic domains
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clustered regions of aligned magnetic atoms. When these regions themselves are aligned with atoms. When these regions themselves are aligned w/ one another, the substance containing them is a magnet.
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Ph Ch 11 Define electromagnet
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a magnet whose field is produced by an electric current. It is usually in the form of a wire coil w/ a piece of iron inside the coil
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Ph Ch 11 Define electromagnetic induction
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the induction of voltage when a magnetic field changes w/ time. If the magnetic field w/in a closed loop changes in any way, a voltage is induced in the loop: voltage induced~number of loops x magnetic field change / time
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Ph Ch 11 Define faraday's law
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the law of electromagnetic induction, where the induced voltage in a coil is proportional to the number of loops, multiplied by the rate at which the magnetic field changes w/in those loops. (The induction of voltage is actually the result of a more fundamental phenomenon: the induction of an electric field)
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Ph Ch 11 Define generator
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an electromagnetic induction device that produces electric current by rotating a coil w/in a stationary magnetic field
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Ph Ch 11 Define transformer
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a device for transferring electric power from one coil of wire to another by means of electromagnetic induction
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Ph Ch 11 Define maxwell's counterpart to faraday's law
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a magnetic field is induced in any region of space in which an electric field is changing w/ time. Correspondingly, an electric field is induced in any region of space in which a magnetic field is changing w/ time
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Ph Ch 11 Intro By whom and in what setting was the relationship between electricity and magnetism discovered?
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Hans Christian, Danish physicist in 1820, in a classroom demonstration
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Ph Ch 11 11.1 In what way is the rule for the interaction between magnetic poles similar to the rule for the interaction between electric charges?
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A magnetic force is similar to an electrical force, in that a magnet can both attract and repel w/out touching and the strength of its interaction depends on the distance between magnets. Magnets always have a North and South pole
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Ph Ch 11 11.1 In what way are magnetic poles very different from electric charges?
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Electrical charges produce electrical forces, regions called magnetic poles give rise to magnetic forces.
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Ph Ch 11 11.2 What two kinds of motion are exhibitied by electrons in an atom?
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by the motion of electric charge
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Ph Ch 11 11.2 What produces a magnetic field?
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electron spin; electron revolution
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Ph Ch 11 11.3 What is a magnetic domain?
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clusters of aligned atoms
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Ph Ch 11 11.3 Why is iron magnetic and wood not?
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wood doesnt have magnetic domains that can be induced into alignment. Iron does.a pattern of concentric circles
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Ph Ch 11 11.3 Why will dropping an iron magnet on a a hard floor make it a weaker magnet?
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because it knocks some of the domains out of alignment
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Ph Ch 11 11.4 What is the shape of a magnetic field about a current carrying wire?
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clusters of aligned atoms
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Ph Ch 11 11.4 What happens to the direction of the magnetic field about an electric current when tho direction of the current is reversed?
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the compass needle turns around, showing the direction of the magnetic field
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Ph Ch 11 11.4 Why is the magnetic field strength inside a current carrying loop of wire greater than the field strength about a straight section of wire?
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because the field lines and therefore magnetic concentration becomes bunched up inside the loop
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Ph Ch 11 11.4 How is the strength of a magnetic field in a coil affected when a piece of iron is placed inside? Defend your answer.
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it produces an electromagnet, because of the alignment of magnetic domains in the iron
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Ph Ch 11 11.5 In what direction relative to a magnetic field does a charged particle move in order to experience maximum deflecting force? Minimum deflecting force?
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The force is greatest when the particle moves in a direction perpendicular to the magnetic field lines. At other angles, the force is less, and it becomes zero when the particle moves parallel to the field lines.
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Ph Ch 11 11.5 Both gravitational and electrical forces act along the direction of the force fields. How does the direction of the magnetic force on moving charged particles differ?
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It acts perpendicularly both to the magnetic field and to the electron beam
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Ph Ch 11 11.5 What effect does Earth's magnetic field have on the intensity of cosmic rays striking Earth's surface?
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charged particles from outer space are deflected by Earth's magnetic field
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Ph Ch 11 11.5 Since a magnetic force acts on a moving charged particle, does it make sense that a magnetic force also acts on a current-carrying wire? Defend your answer.
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yes; simple logic tells you that if a charged particle moving through a magnetic field experiences a deflecting force, then a current of charged particles moving through a magnetic field also experiences a deflecting force
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Ph Ch 11 11.5 What relative direction between a magnetic field and a current-carrying wire results in the greatest force on the wire? In the smallest force?
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The force is strongest when the current is perpendicular to the magnetic fields lines. Smallest force???? (Ask Professor for clarification)
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Ph Ch 11 11.5 What happens to the direction of the magnetic force on a wire in a magnetic field when the current in the wire is reversed?
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The force is strongest when the current is perpendicular to the magnetic fields lines. Smallest force???? (Ask Professor for clarification)
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Ph Ch 11 11.5 What is a galvanometer called when it is calibrated to read current? To read voltage?
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a galvometer is a current indicating instrument; ammeter; voltmeter
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Ph Ch 11 11.5 Is it correct to say that an electric motor is a simple extension of the physics t hat underlies a galvanometer?
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If the design of the galvonometer is changed slightly so the deflection makes a complete turn rather than a partial rotation, it becomes an electric motor. The principal difference is that the current in a motor is made to change direction each time the coil makes a half rotation
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Ph Ch 11 11.6 What was the important discovery made by physicists michael Faraday and Joseph Henry?
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electromagnetic induction
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Ph Ch 11 11.6 State Faraday's law.
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The induced voltage in a coil is proportional to the number of loops, multiplied by the rate at which the magnetic field changes w/in those loops
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Ph Ch 11 11.6 What are the three ways in which voltage can be induced in a wire?
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1~ by moving a loop of wire near a magnet 2~ by moving a magnet near a loop of wire 3~ by changing the current in a nearby loop of wire
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Ph Ch 11 11.7 How does the frequency of induced voltage compare w/ how frequently a magnet is plunged into and out of a coil of wire?
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The frequency of the alternating voltage that is induced is equal to the frequency of the changing magnetic field w/in the loop.
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Ph Ch 11 11.7 What is the basic difference between a generator and an electric motor?
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A motor converts electrical energy into mechanical energy; a generator converts mechanical energy into electrical energy.
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Ph Ch 11 11.7 What is the basic similarity between a generator and an electric motor?
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they are both ac current??? (ask professor)
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Ph Ch 11 11.7 Why does the voltage induced in a generator alternate?
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because the coil is moved back and forth w/in a magnetic field
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Ph Ch 11 11.8 What commonly supplies the energy input to a turbine?
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steam or falling water
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Ph Ch 11 11.8 Is it correct to say that a generator produces electric energy? Defend your answer.
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no it simply converts mechanical energy into electrical energy. Energy is not produced.
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Ph Ch 11 11.9 Is it correct to say that a transformer boosts electric energy? Defend your answer.
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if it is a step up transformer, then yes. If the secondary coils have more loops than the primary coil the the voltage will be increased. If the secondary coils have fewer loops, then the voltage produced will be decreased (a step down transformer).
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Ph Ch 11 11.9 Does a step-up transformer step up the voltage, the current, or the power?
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voltage
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Ph Ch 11 11.9 Does a step-down transformer step down the voltage, the current, or the power?
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voltage
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Ph Ch 11 11.10 What is induced by the rapid alternation of a magnetic field?
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an electric field
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Ph Ch 11 11.10 What important connection did Maxwell discover about electric and magnetic fields?
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A magnetic field is induced in any region of space in which an electric field is changing w/ time
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Ph Ch 11.3 Check Yourself~ Why will a magnet not pick a penny or a piece of wood?
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a penny and a piece of wood have no magnetic domains that can be induced into alignment
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Ph Ch 11.3 Check Yourself~ How can a magnet attract a piece of iron that is not magnetized?
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Domains in the unmagnetized piece of iron are induced into alignment by the magnetic field of the magnet. One domain pole is attracted to the magnet and the other domain pole is repelled. Does this mean the net force is zero? No, because the force is slightly greater on the domain pole closest to the magnet than it is on the farther pole. That's why there is a net attraction. In this way, a magnet attracts unmagnetized pieces of iron
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Ph Ch 11.5 Check Yourself~ What law of physics tells you that if a current carrying wire produces a force on a magnet, a magnet must produce a force on a current carrying wire?
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newton's third law, which applies to all forces in nature
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Ph Ch 11.5 Check Yourself~ What is the major similarity between a galvonometer and a simple electric motor? What is the major difference?
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A galvanometer and a motor are similar in that they both use coils positioned in a magnetic field. When a current passes through the coils, forces on the wires rotate the coils. The major difference is that the maximum coil rotation in a galvanometer is one half turn, whereas the coil in a motor (which is wrapped on an armature) rotates through many complete turns. This is accomplished by alternating the direction of the current w/ each half turn of the armature
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Ph Ch 11.6 Check Yourself~ If you push a magnet into a coil, you'll feel a resistance to your push. Why is this resistance greater in a coil w/ more loops?
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Simply put, more work is required to provide more energy. When your push a magnet into a coil, you induce electric current and cause the coil to become an electromagnet. The more loops in the coil, the stronger the electromagnet that you produce and the stronger it pushes back against you.
