22 - Electric Fields Flashcards

1
Q

Define electric field

A

region in space in which a charge would experience a force acting on it

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2
Q

Define electric field strength + units

A

force per unit positive charge measured in NC^-1

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3
Q

Electric field strength equation

A

E=F/Q
e. field strength = force/charge

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4
Q

Direction of field lines for +ve point charge

A

away from centre

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5
Q

Direction of field lines for -ve point charge

A

towards centre

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6
Q

Direction of field assumes direction __ charge would move

A

+ve charge

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7
Q

Arrows on electric field show…

A

direction of electric field

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8
Q

Relationship between field lines and conductor

A

field lines at right angles (perpendicular) to conductor

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9
Q

how is a stronger field shown

A

field lines closer together

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10
Q

how is a uniform field shown

A

field lines are parallel and equally spaced from each other

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11
Q

Point charges and uniformly charges spheres both produce…

A

radial fields

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12
Q

Define one coulomb of charge

A

The amount of charge passing a point in one second when the current is 1A

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13
Q

Outcome of Coulomb’s isolated charges experiment (Coulomb’s Law)

A

The force between 2 electric charges Q and q is proportional to Qq and inversely proportional to the square of their separation, r

F ∝ Qq/r^2 > F=kQq/r^2

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14
Q

k constant of proportionality is equal to … therefore F =

A

k=1/4πε0
> F=Qq/4πε0r^2

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15
Q

Investigating Coulomb’s law - top pan balance

A

Coat two balls in conductive paint (+ve charge) or touch each to +ve electrode oh high tension supply and charges ball lowers to create mass reading on balance. x by 9.81 to get force.

  • balls are on insulating rods
  • closer initial distance, higher reading, higher force
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16
Q

new equation for E. field strength

A

E=F/Q and F=Qq/4πε0r^2

so > E=Q/4πε0r^2

17
Q

negative force means it is…

A

attractive force

18
Q

similarities between elec. and grav. fields

A

both produce radial fields

19
Q

differences between grav. and elec. fields

A

property that creates fields - mass vs charge
field - always attractive, direction of field always towards object vs repulsive (away) and attractive (towards) fields
diff. field stregth equations F/m vs F/Q (more detailed)

20
Q

elec. field between two parallel plates e.g. capacitor plates

A

is uniform - charge will experience constant force wherever it is placed between the plates

21
Q

new equation for elec. field strength (V)

A

E=V/d
units for E are Vm^-1

derivation using E=F/Q W=Fd W=QV

22
Q

capacitance on parallel plate capacitor depends on…

A

overlap area of the plates (A) and separation of plates (d)

C∝A
C∝1/d
C = εA/d
ε = εrε0 εr>relative permittivity

23
Q

Millikan’s oil drop experiment (process)

A

atomsier fires oil droplets into chamber, friction in tube causes some to be charges (can use x ray source to ionise droplets), droplets fall due to grav. and some fall between plates due to top plate hole, field turned on and -ve particles attract to top +ve plate, pd adjusted for oil to be in equlibrium + stationary

24
Q

Millikan’s oil drop experiment (analysis + conclusion)

A

stationary - Fe = Fg
field off and measurements taken at terminal velocity - Fdrag = Fg

conclusion - Charge is quantised (all multiples of smallest charge recorded, e)

25
motion of electron moving in direction of field
experience deceleration, in opposite direction experiences constant acceleration due to constant electrostatic force. attracrs +ve and repels -ve electrode
26
shape of motion for particle entering field at right angle
parabolic path
27
motion for particle entering field at right angle - horizontal motion
no acceleration, velocity constant time in field > t=d/s
28
motion for particle entering field at right angle - vertical motion
acceleration given by F=ma > a=F/m > a=EQ/m initial velocity is 0 final velocity: v = u + at v = 0 + EQ/m x d/v v = EQd/mv a=EQ/m E=V/d so a =VQ/md
29
area under force separation graph
work done to separate charges or change in electric potential energy
30
why is energy negative
external energy is required to pull the charges apart
31
define electric potential
the work done in bringing a unit charge from infinity to a point. or work done per unit charge using V=E/Q
32
potential energy at infinity is
zero
33
capacitance of a charged sphere equation
C=Q/V and V=Q/4πε0r so C=4πε0r
34
what are equipotential lines
lines linking points of equal electric potential in an electric field