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## Physics 2080; Chapter 23-25 Notes

by: Amanda Biddlecome

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# Physics 2080; Chapter 23-25 Notes Physics 2080

Marketplace > Clemson University > Physics 2 > Physics 2080 > Physics 2080 Chapter 23 25 Notes
Amanda Biddlecome
Clemson
GPA 4.0

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These notes cover Chapter 23: Magnetic Flux and Faraday's Law of Induction and Chapter 25: Electromagnetic Waves.
COURSE
General Physics 2
PROF.
Dr. Pope
TYPE
Class Notes
PAGES
5
WORDS
CONCEPTS
Physics
KARMA
25 ?

## Popular in Physics 2

This 5 page Class Notes was uploaded by Amanda Biddlecome on Thursday March 10, 2016. The Class Notes belongs to Physics 2080 at Clemson University taught by Dr. Pope in Fall 2016. Since its upload, it has received 40 views. For similar materials see General Physics 2 in Physics 2 at Clemson University.

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Date Created: 03/10/16
Physics  2080   Chapter  23:  Magnetic  Flux  and  Faraday’s  Law  of  Induction   March  10,  2016   Amanda  Biddlecome     1)  Induced  Electromotive  Force     -­‐Faraday’s  experiment:  had  primary  circuit  that  induces  current  in  second     circuit       *only  if  current  in  primary  is  changing       *current  in  the  second  circuit  is  zero  if  the  current  in  the  primary  is         constant  and  the  magnetic  field  in  the  iron  bar  is  constant       *current  in  second  circuit  flows  in  opposite  directions  depending  on  if         you  increase  the  current  or  if  you  decrease  the  current       *magnitude  of  induced  current  is  proportional  to  the  rate  of  the         magnetic  field  change:  positive  or  negative     2)  Magnetic  Flux     -­‐used  to  get  induced  emf  (ε)     Φ=BAcosθ   *θ=angle  between  the  normal  to  the  loop  and  the  magnetic  field   2 *unit=Tm =1Wb  (Weber)       -­‐maximum  is  when  θ=0;  minimum  is  when  θ=90     -­‐flux  is  proportional  to  the  number  of  magnetic  field  lines  through  a  loop     3)  Faraday’s  Law  of  Induction     -­‐current  is  induced  in  a  coil  if  the  magnet  and  the  coil  are  in  relative  motion       *this  is  how  electricity  is  generated     -­‐induced  current  is  actually  measured  in  voltage  (emf)     ε=-­‐N(ΔΦ/Δt)   *N=the  number  of  loops/turns   *ΔΦ=change  in  flux     *Δt=time  interval   *we  will  usually  ignore  the  minus  sign  because  we  use  the  right  hand  rules  to   determine  the  direction  of  the  current       -­‐can  change  Φ  by  changing  B  (move  the  loop)  or  changing  A  (squish  it)     4)  Lenz’s  Law     -­‐sign  of  ε  will  produce  I  so  that  B  opposes  ΔΦ  through  the  loop       *voltage  tends  to  maintain  original  flux  through  a  circuit     -­‐if  magnetic  field  increases,  the  flux  increases     -­‐the  current  should  oppose  increasing  flux     -­‐original  magnetic  field’s  sign  is  opposite  of  induced     5)  Moving  Magnets     -­‐magnet  at  rest  has  no  induced  current     -­‐magnet  moving  down  toward  the  loop,  increases  downward  flux;  more  field         lines  through  the  loop     -­‐loop  generates  upward  pointing  field     -­‐counterclockwise  current     -­‐moving  magnet  up,  you  decrease  downward  flux       *downward  pointing  field  is  needed       *downward  pointing  field  is  induced  by  a  clockwise  current     -­‐bar  magnets  and  two  poles  (affect  the  direction  of  the  magnetic  field)     6)  Lenz’s  Law     -­‐have  induced  emf  between  two  poles;  put  the  ring  between  them  and  create     a  temporary  magnet  between  them       *Eddy  Current     -­‐Motional  EMF       *put  conducting  rod  on  a  track;  drop  it  so  it  goes  at  a  velocity  v;  get  a         potential  difference  across  the  rod  (force  RHR);  magnetic  flux  changes       and  you  get  an  induced  current       *conductor  has  a  length  (l),  velocity  (v),  uniform  magnetic  field  (B)       *because  of  potential  difference,  there’s  an  electric  field  (E)       *balance  F=qvB  with  F=qE     E=vB   *says  electric  and  magnetic  fields  are  integrally  related           *electric  field  is  constant       *potential  difference  along  a  long,  current-­‐carrying  wire  in  a  uniform         magnetic  field=Blv     7)  Generators  and  Motors  and  Transformers     -­‐electric  generator  converts  mechanical  energy  into  electric  energy  by     turning  a  coil  in  a  generator       *lakes  help  with  this     -­‐induced  emf  in  a  rotating  coil  varies  sinusoidally     ε=NBAωsinωt   *ωt=angular  frequency         *maximum  induced  emf  is  when  ωt=90  or  270       -­‐energy  stored  in  a  magnetic  field       *inductance     L=NΦ/I     -­‐energy  stored  in  a  magnetic  field  of  an  inductor     2 U=(1/2)LI       -­‐transformer:         *primary  circuit-­‐5  loops,  low;  secondary  circuit-­‐  3  loops,  all  wrapped         around  an  iron  core       *have  alternating  current  in  the  primary  that  produces  an  alternating         magnetic  field  that  produces  current  in  the  secondary  (how  we  power       homes)       *voltage  in  the  primary=larger  than  in  the  secondary       *power  in  both  circuits  have  to  be  the  same     Chapter  25:  Electromagnetic  Waves     1)  Electromagnetic  Waves     -­‐all  of  them  travel  at  the  same  speed     -­‐produced  by  oscillating  charges       *fields     -­‐have  electric  and  magnetic  field  that  are  mutually  perpendicular  and     perpendicular  to  the  direction  of  the  propagation     -­‐Right  Hand  Rule       *BEV:  B  (magnetic  field)=middle  finger;  E  (electric  field)=pointer         finger;  v  (velocity)=thumb;  middle  finger  points  out,  not  up     -­‐all  electromagnetic  waves  go  through  a  vacuum  at  the  same  rate       *Speed  of  Light  (c)=3.00X10  m/s   8     *in  materials,  it  slows  down,  but  not  by  much       *very  large  speed       *gives  the  concept  of  relativity     -­‐measuring  speed  of  light       *Fizeau  shone  light  at  a  mirror  at  a  45  degree  angle;  some  light  was         deflected  and  some  pass  through;  the  light  that  passed  through  then         had  to  be  transmitted  back  through  the  tooth  of  the  wheel;  some  was         transmitted  back  and  some  was  shone  up     -­‐some  light  passes  through  free  space     c=1/(√μ ε )   0 0 *μ =4π010 Ns /C   -­‐7   2 2 *ε =8.05X10  C /Nm   -­‐12 2 2     -­‐light=electromagnetic  wave  and  E/B=c       *all  of  them  travel  at  the  same  speed  “c”       *waves  carry  energy  that  can  be  transferred  to  objects  in  their  path     -­‐what  we  see  in  the  night  sky  are  very  very  very  far  away     -­‐Doppler  Effect       *speed  of  waves  in  a  vacuum  doesn’t  change  but  as  observer  and         source  move,  the  frequency  changes     f =f(1+/-­‐  u/c)         *used  to  tell  speeds  of  storms     2)  Electromagnetic  Spectrum     -­‐Radio,  Microwaves,  infrared,  visible,  ultraviolet,  xray,  gamma  ray     -­‐as  wavelength  increases,  frequency  decreases  and  vice  versa     -­‐transport  energy  and  have  linear  momentum       *can  have  collisions  and  conserve  momentum     c=λf   *c=speed  of  light   *λ=wavelength   *f=frequency       -­‐radio  waves-­‐10 -­‐10  Hz  frequency   9 12   -­‐microwaves-­‐cooking  and  telecommunications;  10 -­‐10  Hz  frequency  and     1mm-­‐30  cm  wavelength       -­‐infrared  waves-­‐tell  if  you’re  giving  off  heat;  frequency=10 -­‐4.3X10  Hz   12 14   -­‐ultraviolet  light-­‐cause  tanning;  some  insects  can  see  this;     frequency=7.5X10 -­‐10  Hz   14 17 17 20   -­‐xrays-­‐medical  uses;  frequency=10 -­‐10  Hz     -­‐gamma  rays-­‐destructive  to  living  cells;  frequency=greater  than  10   20   -­‐we  see  visible  spectrum       *above  visible  light  on  the  spectrum,  they  have  particle-­‐like  behavior         with  increasing  photon  energy       *below  visible  light  on  the  spectrum,  they  have  wave-­‐like  behavior     3)  Polarization     -­‐polarization  direction  allows  electric  field  lines  parallel  to  the  polarization       direction  to  pass  through  and  it  absorbs  all  of  the  waves  that  are     perpendicular  to  the  polarization  direction         *can  have  selective  absorption     -­‐polarized  light  has  electric  fields  in  the  same  direction     -­‐unpolarized  light  has  electric  fields  in  random  directions     -­‐can  polarize  un-­‐polarized  light  by  passing  it  through  a  polarizer       *allows  particular  component  to  pass  through       *use  polarizer  and  analyzer  to  completely  block  light  (cross           polarizers)  by  crossing  transmission  axes     -­‐polarizer  transmits  components  of  light  in  polarization  direction     -­‐use  Malus’s  Law     I=I co0 θ   2   -­‐transmitted  intensity  is  at  a  maximum  when  transmission  axes  are  parallel     -­‐transmitted  intensity  is  at  a  minimum  when  transmission  axes  are     perpendicular

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