Electric Charges and Fields 3 Flashcards
what is an electric dipole
An electric dipole is a pair of equal and opposite point charges q and –q,
separated by a distance 2a.
The line connecting the two charges defines
a direction in space.
By convention, the direction from –q to q is said to
be the direction of the dipole.
The mid-point of locations of –q and q is
called the centre of the dipole.
the ideal dipole is the smallest dipole of almost no size.
what is electric dipole moment
Electric dipole moment measures the strength of electric dipole.
It is a vector quantity.
It is defined as the product of the magnitude of one charge and the seperatio of 2 oppostie charges.
Its direction is along the dipole axis from the -ve to +ve
denote dby p
what is total charge and total field of an electric dipole
the total charge of an electric dipole is 0 but the total electric field of an electric dipole is not 0.
It is because the charge +q and -q are separated by some distance. The electric field due to them, do not exactly cancel out, however at distances much larger than the dipole size the field due to +q and -q nearly cancel out.
what is the electric field of a short dipole related to
electric field is inversely proprtional to the cube of r ( distance b/w centre of dipole and test charge)
angle between E axial and dipole moment? E equatorial and dipole moment?
E axial and dipole moment have angle difference of 0
E equatorial and dipole moment have an angle difference of 180
what are eelctric field lines?
electric field lines is defined as the path along which a unit +ve charge would move in if it is free to do so.
An electric field line is, in general a curve drawn in such a way that the tangent to it at each
point is in the direction of the net field at that point.
basic properties of electric field
- electric field lines are continuous curves. The electric field lines start at a +ve charge and end at a -ve charge.(but they don’t form closed loops). If there is a single charge, they may
start or end at infinity. - the tangent to a line of force at any point denotes the direction of electric field at that point.
- the relative closeness of field lines denotes the relative strength of the electric field.
-(ii) In a charge-free region, electric field lines can be taken
to be continuous curves without any breaks.
what is the total electric field in a conductor? why?
The field lines do not pass through a conductor ie they do not form closed loop beause the electric field inside the charged conductor is 0.
can two electric field lines cross each other?
No two field lines can cross each other because if they do, then there will be 2 tangents at the point intersection hence 2 directions of electric field at the same point which is not possible.
what is the direction of field lines wrt to a conductor
The lines of force are always normal to the surface conductor on which the charges are in equilibrium.
If the lines of force are not normal, then the component of force parallel to the conductor would cause the electrons to move and would set up a current on the surface, but no current flows in equilibirum.
What is neutral point?
point F represents the neutral point, where net electric field intensity is zero.
When the charges are equal, P lies at the centre of the linejoining the charges. However, when the charges are unequal, the neutral point P is closer to the smaller charge as shown in Fig. 1.20.
physical significance of dipole moment
In most molecules, the centres of positive charges and of negative charges*
lie at the same place. Therefore, their dipole moment is zero. CO2
and
CH4
are of this type of molecules. However, they develop a dipole moment
when an electric field is applied. But in some molecules, the centres of
negative charges and of positive charges do not coincide. Therefore they
have a permanent electric dipole moment, even in the absence of an electric
field. Such molecules are called polar molecules. Water molecules, H2O,
is an example of this type. Various materials give rise to interesting
properties and important applications in the presence or absence of
electric field.
what is a point dipole
We can think of the limit when the dipole size 2a approaches zero,
the charge q approaches infinity in such a way that the product
p = q × 2a is finite. Such a dipole is referred to as a point dipole.
what happens when we place a dipole in a uniform electric field
When a dipole is placed in a uniform electric field, two forces act on which are equal and opposite
therefore there is no translatory motion experienced by the dipole
HOwever these 2 forces act at different points and hence a torque is produced, which tries to align the dipole parallel to the electric field,
What happens if the field is not uniform?
In that case,
the net force will evidently be non-zero. In addition there
will, in general, be a torque on the system as before.
let us consider the simpler
situations when p is parallel to E or antiparallel to E. In
either case, the net torque is zero, but there is a net force
on the dipole if E is not uniform.
