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Physics > unit 4 electric field > Flashcards

unit 4 electric field Flashcards

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1
Q

coulomb’s law

A

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

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2
Q

coulomb’s law conditions

A
  1. only apply to point charges

2. the radius of the point charge has to be smaller than the separation

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3
Q

permittivity of free space t

A

formula and the constant with unit

white note

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4
Q

forces btwn point charges in vacuum

give me k with unit

A

8.99 times 10^9

NM^2C^-2

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5
Q

the direction of force in terms of….

A

push and pull

not attract or repel

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6
Q

the graph for

  1. F inversely proportional to r
  2. F proportional to the 1/r^2
A

notes

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7
Q

hanging spheres

draw the free body diagram

work out the angle

give me the conclusion

A

notes

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8
Q

electric field strength

define

formula there’s two

  1. E of A on B
  2. E on a single charged particle
A

force per unit of charge acting on a positive point charge on that point

formula is in the definition itself or refer to notes

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9
Q

electric field

define

A

the region where electrostatic force acts on charged particle

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10
Q

point charge

define

A

the radius of the charge particle is smaller than the separation bwtn the charged particle

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11
Q

who obeys inverse square law

A

E and F

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12
Q

field lines

4 things

point charge
parallel plates
field lines
field line density

A

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

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13
Q

calculation only

  1. electric field strength of A at point B
  2. electric field strength of a single charged particle
  3. electric field strength of 2 charged particles

( identify the direction if the positive point charge )

A

notes on pg 53 and 54

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14
Q
  1. electric field strength of A at point B

the theory

direction
force

A
  1. 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
  2. same force due to N3
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15
Q
  1. electric field strength of 2 charged particles

theory pg 54

at which region the resultant electric field strength can be zero

A
  1. region R
  2. region S , both electric field act in same direction
    - cannot cancel out
  3. region P , electric field strength acts in opposite direction
    - but /E5/ not = to /E -3/
  4. 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/
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16
Q

conducting charged spheres

/E5/ not = to /E -3/

outside field strength and field is identical to

A

E=0 due to Q=0

outside field strength and field is identical to
POINT CHARGE

17
Q

conducting sphere

relate to E against r graph

identify what the graph means

A

notes at 55

18
Q

electric field causes the air to become conducting

A
  1. field produces forces on the electrons
  2. and the nucleus in opposite direction
  3. electrons stripped off from the atom
  4. electrons and positive ion move in opposite direction and giving rise to current
19
Q

conducting sphere

the formula supposed to relate to when r>R

A

pg 54

20
Q

graph of electric field strength btwn 2 point charges

graph on pg 56 interpret them

A

pg 56

21
Q

difference btwn electric and gravitational field

3

A
  1. electric field can be attractive and repulsive, whereas gravitational fields are only attractive
  2. electric fields depends upon the material in which they lie , gravitational ones do not ( is constant )
  3. it is possible to shield things from electric fields but it is impossible to shield things from gravitational field
22
Q

electric field

from… to …..

A

positive to negative

23
Q

relate work done formula with electric potential energy

derive a new formula of

  • electric force
  • electric field strength from it
A

pg 59

24
Q

equipotential surface results in….

near positive plate has greater value

A

a change in formula cause every surface shares different potential difference

so keep an eye on V on all times

25
Q

the graphs for parallel plates

get comfortable with it

pg 61

know what you are looking at interpret the graph

A

pg 61

26
Q

stationary oil drop

which forces are important
which is not

A

electrostatic force

weight

ignore air resistance

27
Q

how stationary oil drop is charged

A

charged by friction when pass through nozzle

28
Q

stationary oil drop

pg 62 determine the charge charge of the oil drop by observing its direction of traveled

why so

A

62

29
Q

stationary oil drop

what happens if the plates move closer

what happens to the forces

  • electrostatic force
  • weight
A

< electrostatic force increases >

but weight remains constant

if oil drop charged negative, oil drop accelerate upwards

F (electrostatic force) - mg = ma

30
Q

stationary oil drop

  1. what happens if mass of one oil drop is greater than the other
    - what must change
  2. what happens if the plates move closer again?
A

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

31
Q

dipole molecule btwn parallel plates

positive at one end and negative at one end

describe the movement of the molecule and how

A

opposite forces act on either end of the molecule

forces not the same line

molecule rotates
-charges align with the charged plates + -

32
Q

show how to draw the path of a charged particle

A

pg 64

labeling of field strength and electrostatic force has different direction

33
Q

the path of a charged particle

horizontal motion:

vertical motion:

A

horizontal motion: constant velocity due to no force in horizontal direction

vertical motion: constant acceleration due to constant upwards electrostatic force

resultant = electrostatic force

34
Q

the path of a charged particle

resultant = electrostatic force

the formula and displacement questions

show calculation

A

pg 64 or brown book red

35
Q

the path of a charged particle

show who is faster

A

pg 65

36
Q

experiment to confirm acceleration / force / field strength is constant btwn parallel plates

A

pg 66

Physics (12 decks)

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