6 Electrical fields Flashcards
fields
regions in which an object will experience a force at a distance
electric field
created by charged objects
other charged objects in this electric field will experience force
electric field strength
efs of an electric field at a point in space is defined as the force experienced per unit positive charge at that point
E=F/Q
efs= force/positive charge
NC-1
efs direction
vector quantity- has direction, direction of the ef at a point is the direction in which a positive charge would move when placed at that point
electric fields point away from positive charges and towards negative charges
electric field patterns
- arrow on an ef line shows direction of field
- ef lines are always at right angles to the surface of a conductor
- equally spaced, parallel ef lines represent a uniform field - one in which the efs is the same everywhere
- closer ef lines represent greater efs
coulombs law
any two point charges exert an electrostatic (electrical) force on each other that is directly prop to the product of their charges and inversely prop to the square of the distance between them
similarities between gravitational and electric fields
- point masses and point charges both produce radial fields
- similar equations for forces and field strengths
differences between gravitational and electric fields
-masses always produce an attractive field, whereas charges can create both attractive and repulsive fields
electric field between two parallel plates
produce uniform ef in region between plates
F=EQ
charge will gain energy as it moves from the positive plate to the negative plate
E=V/d
efs=pd/distance
Vm-1 (or NC-1)
parallel plate capacitor
capacitance of a parallel plate capacitor depends on separation between plates, area of overlap between plates and insulator used between plates
C dir prop A/d
constant of proportionality in this relationship is the permittivity of free space
uniform electric fields
A uniform field is a field which has no dependence upon position i.e. the field is constant in space.
A uniform electric field is produced between two parallel oppositely charged plates.
A particle between such plates is subject to a constant force no matter where it resides between the plates.
electron acceleration between two charged plates
being neg charged, an electron between the plates will travel from the negative plate towards the pos plate, in the opposite direction of the ef.
the electron experiences a constant electrostatic force because of the uniform ef between the plates, so it has a constant acceleration
electron travelling in direction of ef
from pos to neg plate
experiences deceleration
charged particles moving at right angles to an ef
an object thrown horizontally on the surface of earth describes a parabolic path- its vertical motion is affected by the earth’s gravitational pull but its horizontal motion is unaffected.
this is the same when a charged particle enters a uniform electric field at a right angle
electric potential
The electric potential at a single point can be defined as the work done per unit charge to bring a positive charge from infinity to that point.
The electric potential at infinity is often defined as 0.
V=E/q V=Q/4piE0r
force-distance graphs for point and spherical charges
the force between two positive particles of charged Q and q varies with their separation
area under the graph is equal to work done
total work done is same as the electric potential energy E=Qq/4piE0r
electric potential difference
epd between two points is just the difference between the potentials at these two points
capacitance for an isolated sphere
a capacitor is a device that stores charge.
an isolated charged sphere of radius R also stores charge so must be a capacitor
the capacitance of a charged sphere is:
C=Q/V C=4piE0R
equipotentials
an equipotential line is a line, or a surface, along which the electric potential is the same
