Electric Fields Flashcards
Define electric field line:
The path a free positive test charge follows.
Define electric field strength:
The force per unit charge on a positive test charge at that point in the field.
E = F/Q
What makes an electric field uniform?
The field lines are equal in magnitude and all in the same direction.
Electric field strength in uniform field:
E = V/d d is the separation between the plates.
Prove E =V/d
If a charge is moved from the positive to negative plate: W = Fd so W =QEd
Therefore V = QEd/Q = Ed
Therefore E = V/d
What determines electric field strength:
The strength of the charge on the conductor (and where the most of that charge is concentrated)
What is electric field strength proportional to on a plate:
E proportional to Q/A so E * E0 = Q/A where E0 is permittivity of free space.
Which way do field lines go:
Positive to negative.
Permittivity of free space:
charge per unit area on a surface in a vacuum that produces an electric field strength of 1 volt per metre between the plates.
Define electric potential:
Work done per unit positive charge on a positive test charge when it is moved from infinity to that position.
Unit of electric potential:
Volts or Joules per coulomb. V = Ep/Q (v is often change in potential between 2 points)
Equipotential:
Surface of constant potential
Negative and positive potential:
A negative charge has negative potential as energy must be added in order to make the potential zero at infinity. Vice versa for positive.
Potential gradient:
Change of potential per unit change of distance.
Constant in a uniform field and increases in opposite direction to the electric field increase.
Equal to negative of the electric field strength.
Equation relating electric field strength and potential:
E = - change in V/ change in x
