7.3 Electric Fields Flashcards
Coulomb’s Law
states that the magnitude of the force between two point charges is
directly proportional to the product of their charges, and inversely proportional to the
square of the distance between the charges.
When is the force attractive?
When both charges are different
When is the force repulsive?
When both charges are the same
Electric field strength
is the force per unit charge experienced by an object in an electric field.
How to find out whether a
particle is charged, and whether its charge is negative or positive ?
- This is done by firing the particle
at right angles to the field and observing its path - A charged particle will experience a constant
electric force either in or opposite to the direction of the field (depending on its charge), this
causes the particle to accelerate and so it follows a parabolic shape
Difference between radial field and uniform field
- A uniform field exerts
that same electric force everywhere in the field, as shown by the parallel and equally spaced field
lines - whereas in a radial field the magnitude of electric force depends on the distance between
the two charges.
How do you know if the particle has a positive charge from a graph?
The parabolic shape must be in the direction of the field.
How do you know if the particle has a negative charge from a graph?
The parabolic shape must move opposite to the
direction of the field.
How do you know if the charge (Q) is positive from radial field
Electric field lines point away from Q
How do you know if the charge (Q) is negative from radial field
Electric field lines point towards Q
electric potential (V)
is electric potential energy per unit positive charge
At an infinite distance from Q
A charged particle q would have zero potential energy
What does the gradient of a tangent give you
gives the electric point at that point
What happens to the charge in a repulsive field
The charge q gains potential energy as r decreases
What happens to the charge in a attractive field
The charge q gains potential energy as r increases
What does the value of potential ( positive or negative) depend on
depends on the sign of the charge (Q),
when the charge is positive
potential is positive and the charge is repulsive,
when the charge
is negative
potential is negative and the force is attractive
What is the gradient of a tangent to a potential (V) against distance (r) graph
gives the value of
electric field strength (E) at that point
Electric potential difference
is the energy needed to move a unit charge between two
points.
What surfaces to electric fields have
equipotential surfaces
what is the potential on an
equipotential surface
the same everywhere, therefore when a charge moves along an
equipotential surface, no work is done.
How is a uniform field strength produced
by connecting two parallel plates to the opposite poles of a battery
what do you get under the area of a graph of electric field strength (E) against distance (r)
you can find the electric potential difference
when is the absolute magnitude of electric potential at its greatest
at the surface of a charge, and as the distance from the charge increases, the potential decreases
so electric potential at infinity is zero.
Define electric potential at a point in an electric field
The electric potential at a point in an electric field is the work done per unit charge when a point positive charge is moved from infinity to the point.
