Electromagnetism
Electrostatic Charges, Fields and Forces
Electrostatic Charges and Fields
Electrostatic Charge
A stationary charged object which produces an electric field
Point Charge
Charge is in Coulombs (C)
Entire charge of the object is squeezed into a very small size
Might also be represented as e
Which is magnitude of electric charge on on electron 1.6 x 10^-19C
Electrostatic Fields
Electric fields
Tools to draw them
Equipotential lines
Fields
Electric Field Strength
Force is due to Coulomb interaction
Object will experience:
Q = charge
Equation
Electric Field Strength
Charge Size
Force Size
A point in an electric field will always produce an equal force per unit charge
Electric field will be stronger when closer to charge
Constant Electric Field
In Charged Parallel Plates
A charged particle will face the same force regardless of where it is
Repulsion + attraction = Total Force
Positive Charge moving towards Negative Plate
Attraction Increases
Repulsion Decreases
Total Force stays Constant
until hitting the negative plate
Charge will also be Constant
Electric Field Strength will also be Constant
Potential Energy will turn into Kinetic Energy
Through Accelerating
Potential Energy is not Constant
High
Positive Charge is close to Positive Plate
Low
Positive Charge is close to Negative Plate
Potential Energy
Distance to negative plate
Potential Energy
Constant for Charged Parallel Plates
Definition
A region in which a charge will experience a force
(attraction or repulsion)
Types
Positive
Negative
Neutral
May still have positive charges
Simply have more positive charges
Definition
Difference between the number of protons and electrons in an object
Neither a proton or electron would be able to produce a stronger field
Same Charge = Same Field Strength
Direction of Fields Different
Electric Fields Around Objects
Electric Field Line Conventions
Three Golden Rules of Field Lines
- Arrow of field lines = direction a positive charge would move
- Field lines never cross
Field lines only show resultant force
If lines crosses it would show 2 different forces
Field lines only show overall field direction
- Distance between field lines represent their strength
Close lines = Stronger
Uniform Lines = Uniform Field Strength
Drawing Electric Field Lines
Point Charges
Negative
Positive
Stronger Force
Equipotential Line Conventions
Potential
Definition
How much energy a charge would gain by following the path of the field from that point
Equipotential Lines
Join Areas of Equal Potential
Same Field Strength
Same Distance from the Charge
Drawn as:
Circles of Increasing Radius around the Centre
Each line represents
An equal reduction in field strength
Close Electric Fields = Quick Decrease
More Spaced = Decrease Slowly
Shows true shape of the field
Independent of arrow direction
Pair Charges
Bending away represents that positive charges will be repelled
Dipoles
A pair of opposite charges separated by a distance
Line away from point charge gradually weaken
Gradual increase of gap
Charged Parallel Plates
Lines need to be drawn from positive to negative
Work and Charge in Electric Fields
Combining Equations for Field Strength
Work
Charge of Particle
Potential Difference across the Plates
Amount of KE electron gains by moving from negative to positive
Constant
1.6 x 10^19C
1eV
energy required to move one electron through a potential of one volt
Convert to Joules
Multiply by Q
Volt
Joules per Coulomb
Finding Speed
Proton < acceleration
Heavier than electron
Electric Field Strength Between Plates
Subtract charges from each other
Force on Proton
Electric Field Strength
Constant charge
SUVAT Equations in Electric Fields
Find Acceleration
Initial velocity = 0
mass of an electron
9.109 x 10 ^ - 31