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Electric

Fields

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TYPES OF CHARGES

POSITIVE AND NEGATIVE CHARGES

Protons have positive chare ! "#$% & #'(#) C

Electrons have neative chare$ ! (#$% & #'(#) CNe*trons+ Have no chare$ ! '

Chares are ele,entar- particles that ,a.e *p ,atter$

/eas*red in Co*lo,0s 1C2

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E3ECTRIC FIE3DS3a4 o5 chares

Law ofconservation o5chare

In a closed system, the total amount of charge remains the same.

Electric fields Space ro*nd a chare 4here electric 5orce is 5elt$

Electric 5ieldstrenth6 E

Force per unit positive charge on a stationary “test charge” placed atthat point.

Uniform Fields Fields between two oppositely charged placed.  E  !

otion of charge

in an electricfield

The charge follows a parabolic path with constant

acceleration in one direction. (Equations of motion)

3a4 o5 chares

Law ofconservation o5chare

In a closed system, the total amount of charge remains the same.

Electric fields Space ro*nd a chare 4here electric 5orce is 5elt$

Electric 5ieldstrenth6 E

Force per unit positive charge on a stationary “test charge” placed atthat point.

Uniform Fields

otion of charge

in an electricfield

The charge follows a parabolic path with constantacceleration in one direction. (Equations of motion)

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3A7 OF CHARGES

•3I8E CHARGES REPE36 9N3I8E

CHARGES ATTRACT

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law of conservation o5 chare

!he law states that electric chare can neither be

created nor destroyed. In a closed system, the totalamount of charge remains the same. "hen something

changes its charge it doesn#t create charge but

transfers it.

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Electric 5ield+Space1reion2 ro*nd a chare4here electric 5orce is 5elt$

"

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Direction o5 Electric 5ield+

The ,anit*de and direction o5 an

electric 5ield is represented 0- Field

lines or lines o5 5orce that r*n 5ro,positive to neative$

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Electric 5ield strenth6 E!he Electric field strength at a point is the force

 per unit positive charge on a stationary “test

charge” placed at that point$

The *nits o5 Electric 5ield strenth is NC(#

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%harged particles in electric field

&'

('

Using the Field to determine the force

E

EF  Q

=

EF   Q=

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Electric Field Strenth :et4een

Chared Parallel Plates19ni5or, 5ield2

•

7or. done 0- 5orce on the chare ! electrical P$E ained 0- the chare

Fd  ! qV • :*t F ! ;E so replacin F

;Ed!V; which gives us

Ed! V so  E  !

 E  is directl- proportional to the p$d 0et4een the t4o plates and inversel-proportional to the separation o5 the plates$

• 9nits o5 electric 5ield strenth are V ,(# or N C(#

•   d

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)arallel )lates %apacitor 

('

&'"V

'V

d

 

E increases when d decreases

o

E*

σ=

ε

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+

Motion of point charges in electric fields

•  An electron falls towards the positive

plate while moving across the field.

• F=ma= qE

  a = F/m = qE/m

The charge follows a parabolic path with

constant acceleration in one direction.

using kinematics:

In Y-directionConstant acceleration

- !#

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otion of %harged )articles in a Uniform

Electric Field

(e

&'

('F -E ma= =r r r

y

e Ea

m

=

r

/v

vr

θ

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Eample! An electron is proected perpendicularl! to a

downward electric field of E= "### $C-% with a hori"ontal

velocit! %#& ms-%' #ow much is the electron deflected

after traveling $ cm.

0ince velocity in direction does not change,

t!d?#$%?#'(#)?=?#'@