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people handling microchips wear antistatic clothing and work in rooms filled with antistatic flooring explain why
 damage to microchip by charge
 potential difference between chip and body will create an electric field
 flow of charge that could damage inside the chip
 antistatic clothing prevents build up of charge on person
 antistatic flooring prevents transfer of charge

there are only two kinds of charge
positive and negative

charge of the same kind
repel each other

charge of different kinds
attract each other

the amount of charge is called the
quantity of electricity

quantity of positive charge is a
positive number

quantity of negative charge
negative number

charge cannot be
created or destroyed but moved from one object to another or from one part of a body to another

total amount of charge in the body in the transfer process
remains the same

this is called the
law of conservation

electrons and protons carry the
same amount of different charge

quantity of charge e is given on
data sheet

quantity of all charged objects is equal to
either e or its multiple therefor the quantity of charge e is called the elementary charge

Columbus law
the magnitude of F the electrical force exerted by one point charge on another point charge is directly proportional to the magnitudes q1 and q2 and inversely proportional to the square of the distance r between the charges


where k is constant and is
1/4pie_{0} where e_{0} is the permitivity of free space

f is often called the
electrostatic force

regardless of whether the forces are attractive or repulsive they are directed along
the line between the charges and have equal magnitude

each charge exerts a force of magnitude F on the
other

what are the units for electric field strength
 Jm^{1}C^{1}
 JA^{1}s^{1}m^{1}
 ^{}NA^{1}s^{1}

define the electric potential at a point in an electric field
work done per unit charge on a small positive test charge in moving the charge from infinity to the point

if got parallel plates with +3v at top and +1v at bottom the electric field direction is
downwards

an ion travels horizontally and enters a uniform vertical electric field the horizontal component of the velocity of the ion is
unaffected by the electric field

the electric field that exists at a point is the
electrostatic force experienced by a small positive test charge placed at that point divided by the charge itself

electric field is a
vector and its direction is the same as the direction of the force F on a positive test charge

SI unit of electric field
NC^{1}

it is the .... in the environment that create an electric field at a given point
charges

the field exists in a sense that
whenever a positive or negative charge is placed at that point the field exerts a force on the charge

any charge in the environment contributes to
electric field that exists at a point

to determine the net electric field it is necessary to
determine the various contributions separately and then find the vector sum of the contributions

the electric field produced by a point charge q can be obtained in general terms from Columbus first law , magnitude of force on positive test charge =
 F = kq_{0}q/r^{2}
 where q_{0} is the positive test charge

divide by q_{0} to obtain magnitude of electric field
E = kq/r^{2}

so electric field doesn't depend on
test charge

electric field disregards
whether charge is negative or positive

electric field lines go from
positive to negative

of q is positive then
E is directed away from q

if q is negative then E is
directed towards q

in an electric field when moving positive test charge from point a to point b the work done is equal to
difference between the electric potential energy at B and that at A


the work done to move the charge from a to b depends on
the magnitude of the charge


V is the
electric potential energy per unit positive test charge

SI unit of electric potential is
JC^{1} = volt

a positive test charge accelerates from a region of
higher potential to a region of lower potential

conversely a negative test charge accelerates from a
region of lower potential to a region of lower potential

electric potential at a distance r from a point charge is
V = kq/r

the previous expression for v assumes the potential is
zero at infinite distance away from the charge

see diagram from notes in the electric field E the work done required to move a negative test charge from a to b is W=
FΔr

where F is the
magnitude of the applied force directed to the left in opposition of the electric force

where r is the
distance between a and b





if the test charge is moved at a constant speed the magnitude of the applied force equals
the magnitude of the electric force but in the opposite direction so F = EQ

the minus sign in the above equations indicates E is
in the direction of decreasing potential

an alternate unit for electric field E is
Vm^{1}

comparison of electric fields and gravitational fields
source
 gravitational force exists between any two objects with mass
 electric force exists between any two objects with charge

magnitude of force
 newtons law of universal gravitational constant F = GMm/r^{2}
 G is the universal gravitational constant
 Newtons law of gravitation for the force between two point masses is an inverse square law  F Ø 1/r^{2}
 coloumbs law F = 1/4pie_{0} x q_{1}q_{2}/r^{2} where e_{0} is the permitivity of free space
 coloumbs law for the electric force between two point charges is an inverse square law F Ø r^{2}

direction of force
always attractive
can be attractive or repulsive

field strength
is the gravitational force per unit mass g = GM/r^{2 }, so field around a mass is proportional to the quantity of mass and inversely proportional to the square of the distance between the centre of mass M and the point in space where the field is measured
is the electric force per unit charge , E = 1/4pie_{0} x Q/r so field around charge is proportional to the quantity of charge and inversely proportional to the square of the distance between the centre of charge Q and the point in space where the field is being measured

potential in radial field
V = GM/r , gravitational potential energy is the work done per unit mass on a small mass in moving the mass from infinity to that point . gravitational potential is zero at infinity .
V = 1/4pie_{0} x Q/r , electric potential is the work don per unit charge on a positive test charge in moving the charge from infinity to that point . electric potential is zero at infinity .

line of force or field line
path of free test mass in the field
path of free positive test charge in a field

unit of field strength
NKg^{1 }or ms^{2
}NC^{1} or Vm^{1}

unit of potential
JKg^{1}
JC^{1} or V

uniform fields
g is the same everywhere , field lines parallel and evenly spaced
E is the same everywhere , field lines parallel and evenly spaced

