Ch 23: Electric Potential Flashcards
If a positive charge moves in the direction of E, then the field does ___ work on the charge and U ___.
positive; decreases
If a positive charge moves in the opposite direction of E, then the field does ___ work on the charge and U ___.
negative; increases
If a negative charge moves in the direction of E. then the field does ___ work on the charge and U ___.
negative; increases
If a negative charge moves in the opposite direction of E. then the field does ___ work on the charge and U ___.
positive; decreases
The work done on a charge by an electric field does not depend on ___, but only on ___.
the path taken; the start and end points
What is the electric potential energy of two point charges q and q_0?
U= 1/4πϵ • qq_0/r
If two point charges have the same sign, the interaction is ___, the work done is ___ and U is ___ at any finite separation.
repulsive; positive; positive
If two point charges have opposite signs, the interaction is ___, the work done is ___ and U is ___ at any finite separation.
attractive; negative; negative
Why do we never use the phrase, “the electric potential energy of a point charge?”
because potential energy is a shared property of the 2 charges
For every electric field due to a static charge distribution, the force exerted by that field is ___.
conservative
For a single point in an electric field, potential energy is equal to ___.
U = qEy
What is the potential energy associated with the test charge q_0 at a point a?
U = q_0/4πϵ * Σ q_i/r_i
For an electric field, U is defined to be zero when the distance is ___.
infinite
What are two ways to view the electric potential energy difference U_a - U_b?
1) The work done by the electric force when the particle moves from a to b; 2)the work that must be done by an external force to move the particle slowly from b to a against the electric force
electric potential
potential energy per unit charge; V=U/q
volt
unit of potential
voltage
the potential difference between two points
What are two ways to view V_ab, the potential of a with respect to b?
1) The work done by the electric force when a UNIT charge moves from a to b; 2) the work that must be done to move a UNIT charge slowly from b to a against the electric force
What is potential due to a point charge?
V = U/q = 1/4πϵ * q/r
What is potential due to a collection of point charges?
V = U/q = 1/4πϵ * Σ q_i/r_i
What is potential due to a continuous distribution of charge?
V = 1/4πϵ⌠dq/r
What is the work done by the electric force as a test charge moves from a to b?
W_a->b = ⌠Fdl = ⌠qEdl
What is the potential difference as an integral of E?
Va-Vb = ⌠Edl = ⌠Ecos ϕdl
T/F: Va-Vb is independent of the path taken from a to b.
TRUE ;)
Moving with the direction of E means moving in the direction of ___ V.
decreasing
Moving against the direction of E means moving in the direction of ___ V.
increasing
What are the 2 units used to express electric field?
V/m and N/C
What is the electron volt (eV) defined as?
1.602E-19 J
When a particle with charge e moves through a potential difference of 1 volt, the change in potential energy is ___.
1eV
What are the two routes to calculating potential due to a charge distribution?
If you know the charge distribution, you can use 1/4πϵ * Σ q_i/r_i or 1/4πϵ⌠dq/r; If you know how the electric field depends on position, use⌠Ecos ϕdl
Whenever possible solve problems using an ___ approach (___) rather than a ___dynamics approach (___).
energy; electric potential and electric potential energy; dynamics; electric fields and electric forces
equipotential surface
a surface on which V is the same at every point
Field lines and equipotential surfaces are always ___.
mutually perpendicular
In general, field lines are ___ and equipotentials are ___.
curves; curved surfaces
In the special case of a uniform field, field lines are ___ and equipotentials are ___.
straight, parallel, and equally spaced; parallel planes
When all charges are at rest, the surface of a conductor is always ___.
an equipotential surface
When all charges are at rest, the electric field just outside a conductor must be ___.
perpendicular to the surface at every point
When all charges are at rest, the entire solid volume of a conductor is at the same ___.
potential
Charge density on a conductor is ___ and E is ___ where it is more curved.
higher; stronger
