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40 Cards in this Set
- Front
- Back
Define Magnetic field |
a region of space around a magnet that causes a magnetic force on magnetic objects |
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Which ways do magnetic field lines point? |
outside a magnet- north to south inside a magnet- south to north |
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do magnetic field lines cross one another? |
no |
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magnetic field lines are closer together or farther away where magnetic field is stronger? |
closer together |
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magnetic fields are two or three dimensional? |
three |
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Whats Oersted's principle? whenever a charge moves.... |
whenever a charge moves through a straight conductor, a circular magnetic field is created around the conductor |
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how do you use the right hand rule for a straight conductor? |
hold a straight conductor in your right hand (pencil) right thumb points in the direction of the conventional current curled fingers represent magnetic field lines |
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Which hand do you use for electron flow and which hand do you use for conventional current |
electron flow: left hand conventional current: right hand |
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what symbols are used to represent a conventional current going in and going out |
imagine the arrow: x = going in dot = going out |
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the spacing of the magnetic fields (concentric circles) are farther apart as they move away from the wire. what does the greater spacing mean? |
the greater spacing means the strength of the magnetic field is getting weaker |
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how can you control magnetism? |
you can turn it on or off change its strength by increasing or decreasing the current control the direction of the magnetic field by changing the direction of the current |
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who discovered that an electric current in a conductor produces a magnetic field around a conductor? |
Oersted (Hans Christian Oersted) |
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what is a solenoid? |
a coiled conductor |
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what is an electromagnet |
any device that produces a magnetif field as a result of an electric current |
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How can you increase the strength of an electromagnet? |
increase the number of coils, increase the current, and using a material that is easily magnetized like soft iron core |
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What is the right hand rule for a solenoid? |
fingers wrap around the coil = direction of the conventional current thumb = point in the direction of the north magnetic pole |
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what are dipoles |
atoms in a magnet that interact with all the dipoles around them |
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dipoles are random in orientation, but when do they become aligned? |
when a magnetic field is present |
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magnetized dipoles allow the formation of the two poles: ______ |
north and south pole |
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how can you demagnetize a magnet? |
heating the magnet or dropping it some become demagnetized when they are removed from a magnetic field |
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what is magnetic saturation? |
point in which all dipoles are aligned and can no longer align more |
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what is the motor principle? |
a current carrying conductor that cuts across external magnetic field lines experiences: a force perpendicular to both the magnetic field and the direction of the electric current |
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What is the right hand rule for the motor principle? |
fingers of open right hand = pointed in direction of the external magnetic field thumb = direction of the conventional current palm = direction of the force on the conductor |
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Whats a galvanometer |
a sensitive meter for measuring current |
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ammeters are made from |
galvanometers placed in parallel with a resistor with less resistance |
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voltmeters are made from |
placing a galvanometer in series with a resistor with high resistance |
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in a DC motor (Direct current motor), what does the split ring commutator do? |
-interrupts the circuit. -changes direction of the current and magnetic field, and keeps the motor spinning |
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a DC motor consists of a .... |
rotor and stator rotor = loop stator = external magnets |
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what do the brushed do in a DC motor? |
they make physical contact with the split ring commutator to complete the circuit and still allow rotation |
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how can you increase the strength of a motor? |
using a soft iron armature and increasing the number of loops. using more current is undesirable because more energy would be lost to heat. |
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give a brief overview of the history covered in electromagnetism (in chapter 12) |
- Magnes discovered magnetite sticking on his sandals. This led to the invention of the compass - Oersted did an experiment with a compass held around a conducting wire in an electric circuit. This demonstrated the shape of the magnetic field lines which were concentric circles -Andre-Marie Ampere took two parallel wires and sent opposing currents through them. This demonstrated that two field lines pointed in same direction = repulsion two field lines pointed in different direction= attraction -Michael Faraday did an experiment with the liquid mercury thing (pg 563). This showed that a magnetic field can cause a current- carrying conductor to move. |
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in order to produce an electric current, the magnetic field needs to be a) stable/same b) continuously changing |
b) continuously changing |
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what is electromagnetic induction? |
the production of electric current in a conductor within a changing magnetic field eg. Faraday brought a permanent magnet near a conductor and induced a current in the conductor |
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what is the law of electromagnetic induction |
electric current is induced in a conductor whenever the magnetic field in the region of the conductor changes |
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What happened with Faradays investigation of electromagnetic induction when he made Faraday's Ring? |
-closing switch in primary circuit produces a constant electric current in conducting wire -magnetic field produced in primary coil -iron ring becomes magnetized
-change of magnetic field in soft iron ring - induced a voltage and electric current in secondary circuit -once the magnetic field is stable, the current in secondary circuit does not exist -you need a changing magnetic field to induce an electric current |
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the amount of induced electric current can be increased by... |
-coiling the conductor -increasing number of loops -increasing rate of change of the magnetic field -increasing strength of magnetic field |
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What are transformers? |
an electromagnetic device that raise or lower voltage -an alternating current (AC) is critical in producing an alternating current in the secondary coil |
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what are step-up and step-down transformers? |
step-up transformer: a transformer with more secondary windings than primary windings - this raises the AC voltage in the secondary circuit step-down transformer: a transformer with less secondary windings than primary windings - this lowers the AC voltage in the secondary circuit overall; we can lower or raise by changing the number of windings in the secondary circuit |
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what is an electric generator |
a device that transforms other forms of energy into electrical energy |
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why do transformers need an alternating current (AC) to operate continuously? |
law of electromagnetic induction- changing magnetic field is required to induce a current. this can be produced by using alternating current. |