Ch 23: Electric Potential

Question 1

If a positive charge moves in the direction of E, then the field does ___ work on the charge and U ___.

Answer 1

positive; decreases

Question 2

If a positive charge moves in the opposite direction of E, then the field does ___ work on the charge and U ___.

Answer 2

negative; increases

Question 3

If a negative charge moves in the direction of E. then the field does ___ work on the charge and U ___.

Answer 3

negative; increases

Question 4

If a negative charge moves in the opposite direction of E. then the field does ___ work on the charge and U ___.

Answer 4

positive; decreases

Question 5

The work done on a charge by an electric field does not depend on ___, but only on ___.

Answer 5

the path taken; the start and end points

Question 6

What is the electric potential energy of two point charges q and q_0?

Answer 6

U= 1/4πϵ • qq_0/r

Question 7

If two point charges have the same sign, the interaction is ___, the work done is ___ and U is ___ at any finite separation.

Answer 7

repulsive; positive; positive

Question 8

If two point charges have opposite signs, the interaction is ___, the work done is ___ and U is ___ at any finite separation.

Answer 8

attractive; negative; negative

Question 9

Why do we never use the phrase, “the electric potential energy of a point charge?”

Answer 9

because potential energy is a shared property of the 2 charges

Question 10

For every electric field due to a static charge distribution, the force exerted by that field is ___.

Answer 10

conservative

Question 11

For a single point in an electric field, potential energy is equal to ___.

Answer 11

U = qEy

Question 12

What is the potential energy associated with the test charge q_0 at a point a?

Answer 12

U = q_0/4πϵ * Σ q_i/r_i

Question 13

For an electric field, U is defined to be zero when the distance is ___.

Answer 13

infinite

Question 14

What are two ways to view the electric potential energy difference U_a - U_b?

Answer 14

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

Question 15

electric potential

Answer 15

potential energy per unit charge; V=U/q

Question 16

volt

Answer 16

unit of potential

Question 17

voltage

Answer 17

the potential difference between two points

Question 18

What are two ways to view V_ab, the potential of a with respect to b?

Answer 18

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

Question 19

What is potential due to a point charge?

Answer 19

V = U/q = 1/4πϵ * q/r

Question 20

What is potential due to a collection of point charges?

Answer 20

V = U/q = 1/4πϵ * Σ q_i/r_i

Question 21

What is potential due to a continuous distribution of charge?

Answer 21

V = 1/4πϵ⌠dq/r

Question 22

What is the work done by the electric force as a test charge moves from a to b?

Answer 22

W_a->b = ⌠Fdl = ⌠qEdl

Question 23

What is the potential difference as an integral of E?

Answer 23

Va-Vb = ⌠Edl = ⌠Ecos ϕdl

Question 24

T/F: Va-Vb is independent of the path taken from a to b.

Answer 24

TRUE ;)

Question 25

Moving with the direction of E means moving in the direction of ___ V.

Answer 25

decreasing

Question 26

Moving against the direction of E means moving in the direction of ___ V.

Answer 26

increasing

Question 27

What are the 2 units used to express electric field?

Answer 27

V/m and N/C

Question 28

What is the electron volt (eV) defined as?

Answer 28

1.602E-19 J

Question 29

When a particle with charge e moves through a potential difference of 1 volt, the change in potential energy is ___.

Answer 29

1eV

Question 30

What are the two routes to calculating potential due to a charge distribution?

Answer 30

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

Question 31

Whenever possible solve problems using an ___ approach (___) rather than a ___dynamics approach (___).

Answer 31

energy; electric potential and electric potential energy; dynamics; electric fields and electric forces

Question 32

equipotential surface

Answer 32

a surface on which V is the same at every point

Question 33

Field lines and equipotential surfaces are always ___.

Answer 33

mutually perpendicular

Question 34

In general, field lines are ___ and equipotentials are ___.

Answer 34

curves; curved surfaces

Question 35

In the special case of a uniform field, field lines are ___ and equipotentials are ___.

Answer 35

straight, parallel, and equally spaced; parallel planes

Question 36

When all charges are at rest, the surface of a conductor is always ___.

Answer 36

an equipotential surface

Question 37

When all charges are at rest, the electric field just outside a conductor must be ___.

Answer 37

perpendicular to the surface at every point

Question 38

When all charges are at rest, the entire solid volume of a conductor is at the same ___.

Answer 38

potential

Question 39

Charge density on a conductor is ___ and E is ___ where it is more curved.

Answer 39

higher; stronger