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Phy > Chap 6 - electromagnetic forces & its effects, motors, transformer > Flashcards

Chap 6 - electromagnetic forces & its effects, motors, transformer Flashcards

1
Q

https://www.youtube.com/watch?v=79_SF5AZtzo
https://www.youtube.com/watch?v=ltpPhpi-CC4
https://www.youtube.com/watch?v=evWpDrRAyCc
https://www.youtube.com/watch?v=pkzY7QfTowM
https://www.youtube.com/watch?v=7RtBUEZbKmI
https://www.youtube.com/watch?v=IxqUjM8cOcU
https://www.youtube.com/watch?v=7RtBUEZbKmI
https://www.youtube.com/watch?v=IxqUjM8cOcU&t=11s

A
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2
Q

slip rings change contact every half rotation

A
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3
Q

note:
-take I as conventional current direction, ( + ) to ( - )
-take field lines from N to S

A
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4
Q

diff btw coil & solenoid

A

coil = 1 turn
solenoid = multiple turns

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5
Q

define EMF

A

-Electro Motive Force eg, batter, generator
-electrical work done by source to moving an unit charge through the circuit
-max pd btw 2 point in a circuit when no current flows
-measure in V
-when cell is connected to circuit, pd drops because of energy wastage in cell

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6
Q

define induced emf

A

when electromotive force is induced in any conductors when there is relative movement btw conductor & mag field

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7
Q

2 ways to induce emf in conductor

A

-conductor moves, mag field stationary (wire & mag)
-conductor stationary, mag field changes (coil/ solenoid & mag)

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8
Q

what does induced emf do when connected to a complete circuit

A

-makes delocalized electrons move
-flow of electrons produce induced I
*has to be connected to a complete circuit

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9
Q

how does emf work when
-conductor moves, mag field stationary (wire & mag)

A

-conductor (wire) cuts field lines & induced emf in conductor (wire)

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10
Q

how does emf work when
-conductor stationary, mag field changes (coil/ solenoid & mag)

A

-as mag moves through conductor (solenoid), field lines cut through turns on conductor (each individual wire)
-emf induced in coil

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11
Q

ways to measure size of induced emf

A

-sensitive voltameter;
needle will deflect when mag is pushed in/ out of coil, not when stationery
-ammeter if conductor is connected to a complete circuit

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12
Q

state faraday’s law of electromagnetic induction

A

emf induced in a conductor is proportional to the rate of mag field lines cut by the conductor

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13
Q

state Lenz’s law for coil/ solenoid & mag

A

-the direction of an induced emf always opposes the change causing it
= any mag field created by induced emf will try to stop the wire/ magnet from moving in/out the solenoid/ coil

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14
Q

how does Lenz’s law work (solenoid & mag)
(how does moving mag through coil/ solenoid work)

A

1)Mag in
-when N of mag is pushed in coil
-changing mag field induced emf
-induced I
-generates mag field in coil
-end of coil near to mag will be N to oppose mag being pushes in; repel
2) Mag out
-when mag is pushed out of coil
-changing mag field induced emf
-induced I
-generates mag field in coil
-end of coil near to mag will be S to oppose mag being pushes out; attraction

IN: repel OUT: attract
mag: coil: mag: coil:
S N N S S N S N
-constant attraction & repulsion

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15
Q

where are electromagnetic induction used in

A

-electrical generators that convert mechanical E to electrical E
-transformers used in electrical power transmission

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16
Q

2 ways to do induced emf

A

1)wire & mag
2)coil/ solenoid & mag

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17
Q

movement of needle in voltmeter when measuring size of induced emf for solenoid & mag

A

-when mag is stationary ( in & out of coil), no induced emf, no movement of needle
-when mag moves in, induced emf & I, needle moved to 1 side
-when mag moves out, induced emf & I direction changes, needle moves to opposite side

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18
Q

factors that increase the induced emf for coil/ solenoid & mag

A

-add more turns to coil
-move mag faster in & out
-increase strength of permanent mag = more dense field lines = more emf induced

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19
Q

how does moving wire through mag work (wire & mag)

A

-wire is moves up & down btw U shapes mag
-field liens are cut & induced emf

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20
Q

direction of needle in voltmeter when measuring size of induced emf for wire & mag

A

-when wire is stationary ( in & out of coil), no induced emf, no movement of needle
-when wire moves in, induced emf & I, needle moved to 1 side
-when wire moves out, induced emf & I direction changes, needle moves to opposite side

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21
Q

factors that increase the induced emf for wire & mag

A

-increase length of wire
-move wire btw mag faster
-increase strength of mag

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22
Q

factors affecting magnitude of induced emf

A

-speed of movement of wire/ mag; more speed, more emf
-no. turns on coil; more turns cut field lines, more emf (solenoid)
-size of coil; more area of coil, more more wire cuts field lines, more emf
-strength of mag field; more strength, more field lines in an area, more lines cut, more emf

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23
Q

factors affecting direction of induced emf

A

-orientation of poles; switching poles of mag = emf induced in opposite direction
-direction of movement of wire/ mag; reversing direction of conductor/ mag= emf induced in opposite direction

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24
Q

difference between motors & generators

A

motor - convert electrical E to mechanical E (Fleming left hand rule)
uses motor effect, I -carrying conductor in mag field experiences a force, causing it to move
generator - convert mechanical E to electrical E (Fleming right hand rule)
uses generator effect/ electromagnetic induction, conductor moves through mag field, induces emf & I

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25
Q

how to use Flemings’s left hand rule (motors)
I carrying conductor

A

-thumb - direction of the force or motion
-Index finger - direction of mag. field (N to S)
-middle finger - direction of I ( + ) ( - ) (conventional current flow).
-all are perpendicular to each other
FBI

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26
Q

how to use Flemings’s right hand rule (generators)
normal conductor

A

Thumb - direction of conductor’s Motion
Index - direction of mag field (N to S)
Middle - direction of induced I
-all are perpendicular to each other
Mother, Father, Child

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27
Q

describe motor effect (extra)

A

-I carrying wire in between a mag = 2 mag. fields will interact
-causes force on wire to push it out
-wire has to be perpendicular to mag field to get full force, if wire is same direction = no force
-use Fleming’s left hand rule
(I carrying wire experiences a force)

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28
Q

how electric motors work for ac

A

-the I carrying coil will experience a force (motor effect)
-coil will spin because of force
-I travels coil in opposite direction
-coil will spin back to original position
-use a slip ring commutators = force acting on coil will alternate directions (to connect coil to carbon brushes)
-every 180 rotation, coil will go back to org position
-1 turn = 180

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29
Q

how electric motors work for dc

A

-the I carrying coil will experience a force (motor effect)
-coil will spin because of force
-I travels coil in opposite direction
-coil will continue spinning in same direction
-use a split ring commutators = swap ( + ) ( - ) connections every half turn = force acting on coil will always be same direction = coil rotate in same direction
(to connect coil to carbon brushes)
-every 360 rotation, coil will go back to org position
1 turn = 360

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30
Q

how to increase motor effect

A

-increase I
-add more turns to coil (stack them)
-use stronger magnets

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31
Q

describe generator effect/ electromagnetic induction

A

-complete circuit where coil movement is perpendicular to the mag field & either one moves = field lines cut = induced emf = induced I

32
Q

how to increase generator effect (extra)

A

-move wire/ mag more quickly
-add more turns to coil
-use stronger magnets

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70
Q

where do mag field lines happen in when I flows/ 3 diff ways to use right hand grip rule

A

-straight wires
-solenoids
-circular coils

71
Q

mag field in straight wire

A

-made up of concentric circles at the center of the wire
-circular field pattern = wire has no poles

72
Q

right hand grip rule for straight wires
find direction of I/ mag field

A

thumb: direction of I
curled fingers: direction of mag field line (arrow) (clockwise/ anti- clockwise)
-reversing direction of I = reversing direction of field lines

73
Q

mag field in solenoid

A

-turns in solenoid increase strength of mag field because more wire in smaller space
-field lines are similar to bar mag: emerge from N, return to S
-the side that I enters is N pole ( + ) terminal
-center of solenoid = straight field lines (S runs to N)
-outside of solenoid = (N runs to S)

74
Q

right hand grip rule for solenoids
finds N pole of mag field in solenoid/ direction of I flow

A

-wrap solenoid with fingers of right hand
thumb: points to N pole of mag. field (direction of mag field)
curled fingers: direction of I flow in solenoid

75
Q

mag field in circular coil

A

circular coil = 1 turn in solenoid
-field lines: emerge from N, returns to S
-mag field lines depend on direction of I

76
Q

right hand grip rule for circular coils
finds N pole of mag field in coil/ direction of I flow

A

thumb - points to N pole of mag. field (direction of mag field)
curled fingers = direction of I & curl fingers according to it

Phy (11 decks)

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