unit 4 electric field Flashcards
coulomb’s law
the electrostatic force btwn 2 point charges is
proportional to the product of their charges and
inversely proportional to the square of their separation
formula on white notes
coulomb’s law conditions
- only apply to point charges
2. the radius of the point charge has to be smaller than the separation
permittivity of free space t
formula and the constant with unit
white note
forces btwn point charges in vacuum
give me k with unit
8.99 times 10^9
NM^2C^-2
the direction of force in terms of….
push and pull
not attract or repel
the graph for
- F inversely proportional to r
- F proportional to the 1/r^2
notes
hanging spheres
draw the free body diagram
work out the angle
give me the conclusion
notes
electric field strength
define
formula there’s two
- E of A on B
- E on a single charged particle
force per unit of charge acting on a positive point charge on that point
formula is in the definition itself or refer to notes
electric field
define
the region where electrostatic force acts on charged particle
point charge
define
the radius of the charge particle is smaller than the separation bwtn the charged particle
who obeys inverse square law
E and F
field lines
4 things
point charge
parallel plates
field lines
field line density
point charge : radial field
parallel plates : uniform field
field lines :
direction of the electric force acting on a POSITIVE POINT CHARGE
or
the direction of the positive point charge tends to go in the electric field
field line density : represents field strength
calculation only
- electric field strength of A at point B
- electric field strength of a single charged particle
- electric field strength of 2 charged particles
( identify the direction if the positive point charge )
notes on pg 53 and 54
- electric field strength of A at point B
the theory
direction
force
- direction of electric field determines by assuming there is a positive point charge at that point
- the direction of force acts on the point charge = direction of electric field - same force due to N3
- electric field strength of 2 charged particles
theory pg 54
at which region the resultant electric field strength can be zero
- region R
- region S , both electric field act in same direction
- cannot cancel out - region P , electric field strength acts in opposite direction
- but /E5/ not = to /E -3/ - region R , field strength are in opposite direction
- the larger charge is further away
- so it is possible both the field to cancel out if
/E5/ = to /E -3/
conducting charged spheres
/E5/ not = to /E -3/
outside field strength and field is identical to
E=0 due to Q=0
outside field strength and field is identical to
POINT CHARGE
conducting sphere
relate to E against r graph
identify what the graph means
notes at 55
electric field causes the air to become conducting
- field produces forces on the electrons
- and the nucleus in opposite direction
- electrons stripped off from the atom
- electrons and positive ion move in opposite direction and giving rise to current
conducting sphere
the formula supposed to relate to when r>R
pg 54
graph of electric field strength btwn 2 point charges
graph on pg 56 interpret them
pg 56
difference btwn electric and gravitational field
3
- electric field can be attractive and repulsive, whereas gravitational fields are only attractive
- electric fields depends upon the material in which they lie , gravitational ones do not ( is constant )
- it is possible to shield things from electric fields but it is impossible to shield things from gravitational field
electric field
from… to …..
positive to negative
relate work done formula with electric potential energy
derive a new formula of
- electric force
- electric field strength from it
pg 59
equipotential surface results in….
near positive plate has greater value
a change in formula cause every surface shares different potential difference
so keep an eye on V on all times
the graphs for parallel plates
get comfortable with it
pg 61
know what you are looking at interpret the graph
pg 61
stationary oil drop
which forces are important
which is not
electrostatic force
weight
ignore air resistance
how stationary oil drop is charged
charged by friction when pass through nozzle
stationary oil drop
pg 62 determine the charge charge of the oil drop by observing its direction of traveled
why so
62
stationary oil drop
what happens if the plates move closer
what happens to the forces
- electrostatic force
- weight
< electrostatic force increases >
but weight remains constant
if oil drop charged negative, oil drop accelerate upwards
F (electrostatic force) - mg = ma
stationary oil drop
- what happens if mass of one oil drop is greater than the other
- what must change - what happens if the plates move closer again?
the charge of the heavier oil drop inceases same fold to balance the weight
but when the plates move closer the acceleration for both are the same
dipole molecule btwn parallel plates
positive at one end and negative at one end
describe the movement of the molecule and how
opposite forces act on either end of the molecule
forces not the same line
molecule rotates
-charges align with the charged plates + -
show how to draw the path of a charged particle
pg 64
labeling of field strength and electrostatic force has different direction
the path of a charged particle
horizontal motion:
vertical motion:
horizontal motion: constant velocity due to no force in horizontal direction
vertical motion: constant acceleration due to constant upwards electrostatic force
resultant = electrostatic force
the path of a charged particle
resultant = electrostatic force
the formula and displacement questions
show calculation
pg 64 or brown book red
the path of a charged particle
show who is faster
pg 65
experiment to confirm acceleration / force / field strength is constant btwn parallel plates
pg 66
