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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

Which ways do magnetic field lines point?

outside a magnet- north to south


inside a magnet- south to north



do magnetic field lines cross one another?

no

magnetic field lines are closer together or farther away where magnetic field is stronger?

closer together

magnetic fields are two or three dimensional?

three

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

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

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

what symbols are used to represent a conventional current going in and going out

imagine the arrow:


x = going in


dot = going out

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

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

who discovered that an electric current in a conductor produces a magnetic field around a conductor?

Oersted (Hans Christian Oersted)

what is a solenoid?

a coiled conductor

what is an electromagnet

any device that produces a magnetif field as a result of an electric current

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

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

what are dipoles

atoms in a magnet that interact with all the dipoles around them

dipoles are random in orientation, but when do they become aligned?

when a magnetic field is present

magnetized dipoles allow the formation of the two poles: ______

north and south pole

how can you demagnetize a magnet?

heating the magnet or dropping it


some become demagnetized when they are removed from a magnetic field

what is magnetic saturation?

point in which all dipoles are aligned and can no longer align more

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

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

Whats a galvanometer

a sensitive meter for measuring current

ammeters are made from

galvanometers placed in parallel with a resistor with less resistance

voltmeters are made from

placing a galvanometer in series with a resistor with high resistance

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

a DC motor consists of a ....

rotor and stator


rotor = loop


stator = external magnets

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

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.

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.





in order to produce an electric current, the magnetic field needs to be


a) stable/same


b) continuously changing

b) continuously changing

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

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

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

-this induced a voltage and elect...

-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

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

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

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...

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

what is an electric generator

a device that transforms other forms of energy into electrical energy

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.