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## Physics 2080, Chapter 19 Notes

by: Amanda Biddlecome

45

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# Physics 2080, Chapter 19 Notes Physics 2080

Marketplace > Clemson University > Physics 2 > Physics 2080 > Physics 2080 Chapter 19 Notes
Amanda Biddlecome
Clemson
GPA 4.0

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These notes cover all of Chapter 19: Electric Charges, Forces, and Fields.
COURSE
General Physics 2
PROF.
Dr. Pope
TYPE
Class Notes
PAGES
4
WORDS
CONCEPTS
Physics
KARMA
25 ?

## Popular in Physics 2

This 4 page Class Notes was uploaded by Amanda Biddlecome on Thursday February 4, 2016. The Class Notes belongs to Physics 2080 at Clemson University taught by Dr. Pope in Fall 2016. Since its upload, it has received 45 views. For similar materials see General Physics 2 in Physics 2 at Clemson University.

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Date Created: 02/04/16
Physics  2080   Chapter  19:  Electric  Charges,  Forces,  and  Fields   February  2,  2016   Amanda  Biddlecome     1)  Electric  Charge     -­‐nucleus       *protons+neutrons       *small,  condensed       *surrounded  by  a  cloud  of  charge  (electrons)     -­‐you  can  rub  charge  off  of  one  material  and  transfer  it  to  another  (NOT     CREATING  CHARGE)       *each  material  transfers  a  different  type  of  charge  and  a  different         amount  of  charge  depending  on  their  valence  electron  shells     -­‐bring  similarly  charge  rods  together  and  they  will  repel     -­‐bring  oppositely  charge  rods  together  and  they  will  attract     -­‐the  net  charge  in  the  universe  can’t  change       *conservation  of  charge       -­‐electrons  are  what  move  between  materials     -­‐all  electrons  have  the  same  amount  of  charge       *e=1.6*10  C   -­‐19     *electrons=-­‐e       *protons=+e     -­‐the  unit  of  charge  is  the  Coulomb   18     *6.25*10  electrons  in  one  Coulomb     -­‐the  mass  of  a  proton  and  the  mass  of  a  neutron  are  almost  equal  but  the     mass  of  an  electron  is  much  smaller       *m =9.11e10  kg   -­‐31     *m =1.67p*10  kg   -­‐27 -­‐27       *m =1.67n*10 kg       *a  neutron  is  just  a  proton+electron     -­‐electrons  in  a  cloud  around  the  nucleus  can  be  separated  easily     -­‐electric  charge  is  conserved  and  is  quantized  so  we  know  the  value  of  e     -­‐positive  ion=lost  an  electron     -­‐negative  ion=gained  an  electron     -­‐charged  objects  can  attract  neutral  objects       *one  type  of  charge  will  be  pulled  and  one  charge  will  be  repelled  and         the  object  will  be  polarized     2)  Insulators  and  Conductors     -­‐conductors=material  whose  conduction  elections  can  move  freely     throughout  the  object       *most  metals  are  conductors     -­‐insulators=material  whose  electrons  don’t  usually  move  from  atom  to  atom       *stable       *most  nonmetals       -­‐electrons  spread  evenly  over  the  surface  of  a  conductor     -­‐semiconductors=properties  between  insulators  and  conductors     -­‐photoconductors=become  conductors  when  light  shines  on  them     3)  Coulomb’s  Law     -­‐materials  have  to  be  close  together  to  transfer  electrons     -­‐force  given  here  is  not  given  a  direction  so  you  have  to  use  the  context  of  the     problem  to  decide  what  the  direction  is       F=k[(q q )/r ]1 2  2   *F=force  (N)   *k=Coulomb’s  constant=8.99*10  Nm /C   9 2 2 *q 1 and  q =abs2lute  value  of  the  charges   *r=the  distance  between  the  two  point  charges   *this  force  can  repel  or  attract  (direction)   *this  force  obeys  all  of  Newton’s  laws         -­‐forces  come  in  action-­‐reaction  pairs     -­‐to  find  net  force  when  multiple  forces  are  present,  add  the  vectors  in  tip-­‐to-­‐   tail  fashion  or  find  the  x  and  y  components  and  use  those  to  find  the  force     2 2 F=√(F +F ) x y   *F=force   *F =sxm  of  the  x  components   *F =sym  of  the  y  components     4)  Electric  Field     -­‐produced  by  charges       *can  draw  an  image  to  visualize  these     -­‐representation  of  what  these  electric  forces  are     E=F/q   0   *E=Electric  field   *F=magnitude  of  force  on  the  test  charge   *q =test  charge:  always  small  and  always  positive   0       -­‐Michael  Faraday  said  that  charge  fills  space  with  an  electric  field     -­‐test  charge  is  pushed  away  from  positive  charges       *test  charge  is  pulled  towards  negative  charge       *the  electric  fields  for  positive  and  negative  charges  are  opposite     -­‐F=qE       *direction  depends  on  the  sign  of  the  charge  and  the  sign  of  the         electric  field       *if  positive  charge  is  in  a  positive  field,  the  force  will  pull  to  the  right       *if  a  negative  charge  is  in  a  positive  field,  the  force  will  go  anti-­‐parallel       to  the  electric  field  (so  left)     -­‐electric  fields  can  be  superimposed  to  add  them  graphically     -­‐electric  dipole       *when  you  have  a  positive  charge  and  a  negative  charge       *the  electric  field  starts  on  the  positive  charge  and  terminates  on  the         negative  charge  (will  be  curved)     5)  Electric  Field  Lines     -­‐point  in  the  direction  of  the  field  vector  anywhere  in  space     -­‐start  at  a  positive  charge  or  at  infinity     -­‐end  at  a  negative  charge  or  at  infinity     -­‐they  are  more  dense  where  the  field  is  stronger     -­‐electric  field  lines  cannot  cross,  so  they  will  bend  when  they  come  near  to     other  electric  field  lines     -­‐the  greater  the  magnitude  of  the  charge,  the  more  field  lines;  therefore,  the     stronger  the  electric  field         *positive  and  negative  are  the  same,  but  different  directions     -­‐we  can  never  draw  all  of  the  possible  electric  field  lines     -­‐when  you  have  two  like  charges,  there  will  be  a  small  space  between  them     where  there  will  be  no  electric  field  lines     -­‐you  can  generate  an  electric  field  with  a  parallel-­‐plate  capacitor       *two  plates  with  opposite  charges       *have  electric  field  lines  from  the  positive  to  the  negative  plate       *between  the  plates  you  have  a  uniform  electric  field  because  charges         distribute  evenly  throughout  a  conductor     6)  Shielding     -­‐electrostatic  equilibrium  is  when  charges  aren’t  moving       *have  to  have  an  isolated  conductor  (can’t  touch  the  ground)  to  have         electrostatic  equilibrium       -­‐electric  field  is  zero  everywhere  inside  the  conductor     -­‐any  charge  lies  entirely  on  the  surface  of  the  conductor       -­‐electric  field  lines  are  perpendicular  to  the  surface     -­‐in  irregular  objects,  charge  accumulates  at  sharp  points  because  it’s  harder     for  charges  to  separate  there       *this  is  what  makes  lightning  rods  effective     7)  Electric  Flux       -­‐measure  of  electric  field  perpendicular  to  the  cross-­‐sectional  area       *only  the  component  that  is  perpendicular  to  the  field  is  used     φ=EAcosσ   *units=Nm /C   2 *φ=flux   *E=electric  field   *A=cross-­‐sectional  area   *σ=angle  formed  with  the  surface  and  the  field       8)  Electric  Flux  and  Gauss’s  Law     -­‐Gauss’s  Law  says  that  flux  through  a  closed  surface  is  proportional  to  the     charge  enclosed  by  the  surface     φ=q/ε   0   *φ=flux   *q=charge   *ε =0ermittivity  Of  Free  Space:  1/(4πk)=8.85X10  (C /Nm )   -­‐12 2 2

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