2. Fields (electrical) / Capacitors Flashcards
Electric field strength
the force per unit charge
Uniform electric field strength
the volts per meter
Which way does charge flow
postive to negative
Electric field strength equation
E = F / Q
What quantity is electric field strength
Vector
What quantity is potential
Scalar
Force upon charges equation
F = 9x10⁹ (Q1 x Q2 / r²)
Electrical Field strength equation 2
E= 9x10⁹ x (Q/r²)
Voltage definition
The energy transferred per unit charge
Potential equation
Ve = 9x10^9 x (Q/r)
Potential definition
The work done is bringing unit positive charge from infinity to a point
What happens when an electron moves past a negatively charged particle?
The electron looses KE because it is fighting against the repulsive force
Change in potential energy equation
W = q x change in Ve
What is electrical field strength on a Ve against r graph
the negative gradient
What is the potential difference on a E against r graph
The area under the line
Potential energy of a point charge equation
qVe = 9x10^9 x (Q1 x Q2 / r )
What does the potential energy at infinity equal to?
The KE
What is a uniform electric field?
A field that has the same strength electric field all the way around
How would you change the electric field strength in a uniform situation
increase the charge on the plates
change the distance between the plates
Uniform electric equation
E = V /d
Definition of capacitance
amount of charge stored per unit of potential difference
Capacitance equation
C= Q / V
Parallel capacitors equation
C = 8.85x10^-12 x A / d
A = area of plates
d = distance between plates
Electric field in a Capacitor
E = V / d
Work done in capacitor
W = change in Q x V
Energy stored in capacitor
½ CV²
How do you change the capacitance without changing the dimensions
Add a dielectric
Change the type of material
As charging Q against T graph
Increasing to a maximum then levelling off
As discharging Q against T and I against T
Decreasing exponential graph
Discharging equations
Q/V/I = (inital Q/V/I) x e^-t/RC
What is RC
RC = time constant
also time to reduce 37% of value
What is a capacitor
Two parallel conducting plates separated by an insulator
How do the graphs for charging and discharging capacitors differ?
Charging has a positive reciprocal gradient compared to the negative reciprocal gradient of discharging
What is coulombs law
The force experienced between two point charges is proportional to the product of their charges and inversly proportional to the distance
For a charged sphere where is charge acting
at the centre of the sphere
What is air treated as when using the electric fields equations
A vaccum
Definition of electric potential
The potential energy per unit charge of a positive charge
How do you measure uncertainty from lots of values
Range / 2
