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physics paper 2 > electric fields > Flashcards

electric fields Flashcards

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1
Q

electric field

A

region of space in which charged particles are subject to an electrostatic force

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2
Q

what shape of field do point charges have

A

radial fields

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3
Q

how can you model uniformly charged spheres

A

as a point charge at the centre of the sphere

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4
Q

what do field lines show

A

path a positive test charge would take when placed in a electric field

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5
Q

which direction do the field lines point

A

+ to -
the lines always point away from a positive charge and towards a negative

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6
Q

what effect does distance on the strength of the electrostatic force

A

the greater the distance the weaker the force

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7
Q

how is the strength of an electric field represented in a diagram

A

how close together the field lines are = the closer the lines the stronger the field

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8
Q

electric field strength

A

force per unit charge on a positive test charge placed in the field

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9
Q

formula fro electric field strength

A

E = F / Q

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10
Q

coulombs law

A

force between any two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them

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11
Q

what is the formula for the force between two point charges

A

F = Q1Q2/4piE0R^2

E0 = permittivity of free space
R^2 = distance between the charges

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12
Q

define permitivity

A

ability of a material to transmit an electric field (how easily the atoms become polarised)

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13
Q

formula for the electric field strength of a point charge

A

E = Q/ 4piE0R^2

can be derived using E = f/Q and the formula for force (coulombs law)

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14
Q

some similarities between gravitational and electric fields

A
  • both follow inverse square law
  • point masses and point charges both produce a radial field
  • newtons law and coulombs law formulae for force are very similar
  • field strength is defined by force per unit charge/mass
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15
Q

differences between gravitational and electric fields

A
  • gravitational fields are always attractive, electric fields can be attractive or repulsive depending on the charge
  • the constants of proportionality in newton’s law and coulombs law are different
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16
Q

fromula for work done when moving a charge in an electric field

A

force x distance

17
Q

define potential at a point in an electric field

A

the work done per unit charge in moving a positive test charge from infinity to that point in the electric field

18
Q

formula for the potential at a point in an electric field

A

V = W/Q

W= work done
Q = charge
v = potential

19
Q

formula for the potential between two parallel plates

A

v = Ed

e = electric field strength
d = distance between the plates

20
Q

formula for the capacitance of a parallel plate capacitor

A

C = Ae0er/d

A = area of plates
e0 = permittivity of free space
er = relative permittivity of dielectric
d = distance between the plates

21
Q

what can the motion of charged particles in an electric field be modelled as

A
  • projectile motion: the twi components of velocity are independent of each other
  • velocity perpendicular to the field is not affected, velocity parallel to the field is
22
Q

how do you calculate the parallel component of velocity for a charged particles in a uniform electric field

A
  • first calc the time the particle is in the field using d/s where the list = length of charged plates and speed is the velocity perpendicular to the field
  • use a = f/m and f = Eq to calc the acceleration of the particle while it is in the field
    a = eq/m
  • substitute these values into v = u+at where u is the initial parallel velocity and v is the final parallel velocity
23
Q

formula for the potential near a point charge

A

V = Q/4piE0r

24
Q

what does the force-distance graph for a point/spherical charge look like

A

exponential decay curve
force is inversely proportional to the square of the distance

25
Q

what does the area under a force-distance graph for a point/spherical charge represent

A

the work done in moving the charge

26
Q

formula for electric potential energy near a point charge

A

E = Vq

27
Q

what is the formula for the capacitance of an isolated sphere

A

isolated spheres can store charge so technically they can be classes as capacitors
using c = q/v and the formula for v you can derive capacitance

C = 4Pie0r

r = radius of sphere

28
Q

formula for electric potential energy near point charge

A

E = Q1Q2/4PiEor

physics paper 2 (8 decks)

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