Chapter 22 Electric Fields Flashcards
What is the definition of electric field strength?
The electric field at a point in space is the force experienced per unit of positive charge at that point
What is the equation for electric field strength?
E = F / Q E = electric field strength F = force Q = the amount of positive charge
How are electric fiend patterns mapped?
- Arrows on the lines show the direction of the field
- Electric field lines are always at 90* to the surface of the conductor
- Equally spaced lines indicate a uniform field
- Closer electric field lines represent greater electric field strength
Is electric field strength a scalar or a vector?
vector, it has a direction
What is coulombs law?
Any two point charges exert an electrostatic force which is proportional to the product of their charges and inversely proportional to the square of their distances
What is the equation for coulombs law?
F = Qq / 4πε0r^2
How can coulombs law be investigated?
Two spheres are given each the same charge
One is hung from an insulated rod and the other is held up with an insulating support on top of a balance. They are brought close together a known distance and the change in mass is calculated. And coulombs law equation is used
What is the equation for the electric field strength for radial fields?
E = Q / 4πε0r^2
Why is the equation for a radial field different?
Because as you move further away from a radial field the field lines spread out so the force experienced becomes reduced so the charge of the other charge does not need to be factored in.
What is ε0?
It is the permittivity of free space
What is the main difference between gravitational fields and electric fields?
Gravitational fields are always attractive
What type of field is produced between parallel plates?
A uniform field
What is the equation for electric fields between two parallel plates?
E = V / d E = Electric field strength V = Potential difference d = Distance between the two parallel plates
How is E = V / d derived?
W = Fd VQ = (EQ)d E = V / d
What is the equation for a parallel plate capacitor?
C = εA / d C = Capacitance ε = The relative permittivity A = Area of plate d = Distance between plates
What relative permittivity?
This is the relative permittivity to ε0.
ε = εr x ε0
εr for a vacuum is defined as 1 because ε0 is for a vacuum
What is the equation for the work done on an electron moving through a uniform field?
Work done = Ve
V = Voltage
e = Elementary charge
What happens when a charged particle enter a uniform field perpendicular to the direction of the electric fields?
It moves toward the plate with the oposite charge. It follows a parabolic path
How can the path of a charge particle in a uniform field be calculated?
The path can be broken down into vertical and horizontal components.
Horizontal has no acceleration so the distance moved(L) = Vt
For vertical we can use F=ma and E = F/Q
Rearranged and combined: a = EQ / m
and v = u + at can also be used
All combined is EQL / mv
What is the area under a force distance graph equal to?
It is equal to the work done
What is the are under a force distance graph equal to for two oposite charges?
It is equal to the work done to separate the charges
What is electric potential?
It is defined as the work done per unit charge in bringing the positive charge from infinity to that point
What is electric potential difference?
It is the work done per unit of charge between two points around the particle of charge
What is the equation for the capacitance of charged spheres?
C = 4πε0R
