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A LEVEL PHYSICS > 22 - Electric Fields > Flashcards

22 - Electric Fields Flashcards

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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
Q

motion of electron moving in direction of field

A

experience deceleration, in opposite direction experiences constant acceleration due to constant electrostatic force. attracrs +ve and repels -ve electrode

26
Q

shape of motion for particle entering field at right angle

A

parabolic path

27
Q

motion for particle entering field at right angle - horizontal motion

A

no acceleration, velocity constant
time in field > t=d/s

28
Q

motion for particle entering field at right angle - vertical motion

A

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
Q

area under force separation graph

A

work done to separate charges or change in electric potential energy

30
Q

why is energy negative

A

external energy is required to pull the charges apart

31
Q

define electric potential

A

the work done in bringing a unit charge from infinity to a point.

or work done per unit charge using V=E/Q

32
Q

potential energy at infinity is

A

zero

33
Q

capacitance of a charged sphere equation

A

C=Q/V and V=Q/4πε0r

so C=4πε0r

34
Q

what are equipotential lines

A

lines linking points of equal electric potential in an electric field

A LEVEL PHYSICS (21 decks)

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