electrostatic forces homework: complete handout. magnitude of force according to coulomb’s law ...
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Electrostatic Forces
Homework: Complete handout
Magnitude of Force
According to Coulomb’s Law The magnitude of force exerted on a charge by
another is directly proportional to the product of the two charges inversely proportional to the distance between the
charges
Equation for calculating the magnitude of an electrostatic force
F = k q1 q2
r2
Where, q = the charger = distance between 2 charged objects
k=8.99 x 10 9 Nm2/C2
force between 2 objects may either attract or repel depending on sign of charges
Calculate the Force exerted between a proton and an electron at a distance of 50 cm.
Electric Fields
Definition: the area around a charged particle that it can exert a force on another charge
Fields can be represented showing field lines (imaginary lines showing direction that a positive test charge would move)
Electric Field for Positive and negative charges
Field lines always start at the positive charge and move toward negative charges
Electric Fields between 2 particles
Electric Field Strength
The ratio of the force exerted on a test charge to the charge of the test charge
E = Fe / q
Units: Newtons per coulomb
Electric Potential (V)
the work done or energy acquired moving a positive test charge between two points in an electric field
Potential Difference (Voltage)
potential energy difference between 2 points in an electric field per unit of charge
as charges move through an electric field, they will either gain KE or PE
Consider: If opposite charges move closer to one another
Gain KE
Potential Difference (Voltage)
If opposite charges move farther apartGain PE
If like charges move closer to one anotherGain PE
If like charges move away from one anotherGain KE
Calculating the Potential Difference
DV = W / qWhere, W = work done against the field, or the energy
acquired working in the fieldq = amount of charge moving through the fieldV = potential difference
Units: Volts (V) = Joule / Coulomb
It takes 6 J of work to move 2 C of charge between 2 points in an electric field.
What is the potential energy difference (V) between these points?
DV = W / qV = 6 J/2 C
V = 3 J/C or 3 V
If 4.8 x 10-17 joules of work is required to move an electron between 2 points in an electric field, what is the electric potential difference between these points?
V = W/q
V= 4.8 x 10-17 J / 1.6 x 10-19 C
V = 300 V
Electric Fields between 2 parallel plates
the electric field that exists between two parallel charged plates is uniform
Electric Potential Difference in a Uniform Field
Equal to the product of electric field intensity (E) and the distance moved by the charge
DV = E d
Electric potential increases in the direction opposite the electric field direction. (it is higher near the + charged plate
What work is done when 3.0 C of charge is moved through an electric potential difference of 1.5 V?
A 12 V car battery can store 1.44 x 106 C of charge when it is fully charged. How much work can be done by this battery before it needs recharging?