Student Responses to Reading Quiz #4, due Monday Feb. 2
Question 1: What is the relationship between electric potential and electric potential energy?
What are the units of potential and potential energy?
1. U = qV Units: Potential J/C Potential Energy J
2. Electric potential is electric potential energy per charge. Electric Potential is in Volts or Joules per
Coulomb. Electric Potential energy is in Joules.
3. U=q*V, where U is potential energy, q is test charge, and v is electric potential. This only works when
the electric potential and potential energy both have chosen zero to be at the same point. The units of
potential are Joules/coulomb. The units for Potential energy are the Newton*Meter.
4. If both of them of a test charge are chosen to be zero at the same point, then U = q V. Unit of V: V Unit
of U: J
5. If electric potential, V, and electric potential energy, U, af some test charge, q, are chosen to be zero at
the same point then U=q*V. The units of electric potential are Volts(V). The units of electric potential
energy are joules(J).
6. Electric potential is the electric potential energy diveded by a charge. U is the potential energy between
two charges and V is the potential that lies at a certain point because of a charge. potential: V (volt) = J/C
(joules/coulumb) potential energy: U = J (joules)
7. Electric potential energy is a potential energy due to an electric field proportional to a test charge q(0)
within that field. However, the potential difference is proportional to the energy change per unit charge,
without any proportionality to the size of a test charge in the field. Potential energy, as always, is in
Joules. Potential is in Joules per Coulomb, a.k.a. Volts.
8. The electric potential is the potential energy per unit charge. The units of potential is a volt, or a joule
per coulomb, and the unit of potential energy is of course a joule.
9. electric potential is the potential energy per unit charge. the unit for potential is volts.
10. Electric potential is the electric potential energy change per unit charge. Potential is in volts (V) or
joules per coulomb (J/C). Potential energy is in joules.
11. The change in electric potential is equal to the change in electric potential energy divided by the
charge of the test charge, so it is the potential energy change per unit charge. Electric potential has units
of joules/coulomb, also called volts.
12. Electric potential energy is electric potential time some charge. The units of potentail are volts or J/C.
The units for potential energy are Joules.
13. The potential energy per unit charge is a function of the position in space of the charge and is called
the electric potential
14. 1. an electric field is a vector, but electric potential is a scalar 2. electric field is inversely prepotional to
r^2 whereas electric potential is inversely preportional to r
15. Electric potential is the work per unit charge that is necessary to move a charge between two places
with unlike potential energy. Also, potential is the change in potential energy divided by the charge that is
moved. Potential is measured in J/C, whereas potential energy is measured in J.
Question 2: The formulas for electric field and electric potential are similar in many ways.
What are two important ways that they are different?
1. You can set potentials to whatever value you want, as we did with potential energy. Potential is
continuous, unlike electric field.
2. An electric field is a vector with magnitude and direction while electric potential is a scalar with
magnitude and +/-. An electric field is inversely proportional to r squared while potential is inversely
proportional to r.
3. Electric potential is continuous everywhere. The Electric field is not. The electric potential depends on
your choice of zero. The electric field does not. Electric potential is inversely proportional to r, not r^2 as is
the case with the electric field. Potential is a scalar, while electric field is a vector. I'm not sure which of
these are important.
4. - V: scalar, E: vector (E = grad V) - Units: V: Volt; E: V/m
5. One important way is that the electric field is an inverse square relationship while electric potential is
just an inverse relationship with distance. The electric field is also a vector quantity in the form of r(^) but
potential is a scalar function.
6. V has a linear proportionality to r, E is proportional to r^2. E is a vector, V is scaler
7. Electric field is a vector function, while electric potential is a scalar function. Electric field is proportional
to 1/r^2, and electric potential is proportional to 1/r. Also, potential generally is only meaningful when the
change between two points is considered and not merely point values, while electric field at one point can
be meaningful. Finally, potential is continuous anywhere there is not a point charge.
8. The electric field is a vector equation, while electric potential is scalar. Also, electric field is
discontinuous but potential is continurous anywhere there is not a point charge. Also, the equations of the
two indicate that electric field is proportional to 1/r^2 and electric potential is proportional to 1/r.
9. electric field is a vector function, while potential is a scalar function. potential is defined with a
differential equation because only changes in potential are important.
10. Electric potential is scalar, while electric field is a vector. Also, the potential is a function of position.
11. Electric potential is a scalar function, while electric field is a vector function. Also, unlike the electric
field, only changes in potential have significance--the function's zero point is completely arbitrary.
12. The formula for the electric field is inversely proportional to the disance squared where as the formula
fo the electric field is inversley proportional to the distance. The other difference is that the electric field is
a vector while the electric potential is a scalar and does not depend on direction.
13. electric potential is inversely proportional to the distance, but the electric field is inversely proportional
to the distance squared.
14. The electric potentential is higher at point A because the electric field did work on the particle to bring
it closer to the source charge
15. First, electric potential is inversely related to distance, but only linearly (1/r). Second, potential is
relative to the potential of any arbitrary point.
Question 3: An electron is released from rest at point A and moves towards point B. Is the
electric potential higher at point A or point B? Briefly explain your reasoning.
1. Potential moves parallel with the electric field. Electron goes towards the source of the field, which
decreases the potential. Therefore B is the source of the field and A has greater potential.
2. Since the charge on the electron is negative, it flows to the area with greater electric potential. Point B
has a greated electric potential.
3. For an electron to be accelerating toward the charge, the charge must be positive. Therefore, the
electric field lines point outwards. Electric field lines point in the direction of decreasing electric potential,
so the electron must be gain potential.
4. No. An electron moves from a lower potential to a higher potential. This means V_A < V_B
5. If you release an electron in an electric field it will feel a force in the direction opposite to the electric
field because of its negative charge and accelerate in the direction opposite of the field lines. Therefore,
because electric field lines point in the direction of decreasing electric potential, the electric potential at
point B would be greater.
6. It is higher at point A. electric potential is like gravitational potential. Things move from a higher
potential energy to a lower by converting to kinetic or another type of energy. A was at rest with X
potential energy, some was converted to kinetic for it to move to B. At B its potential energy is X - Kinetic
Energy.
7. The electric potential at point B must be lower, because charges move toward regions of lower electric
potential energy, analogous to masses and gravitational potential energy.
8. It is higher at point A because charges move towards areas of lower electric potential, which is why the
electron is moving towards point B.
9. the electric potential is higher at point b, because electrons move to areas of high potential.
10. The electric potential is higher at B. The electric field points from positive to negative charges, so the
electric field lines point from B to A, since the electron moves toward B. Since the field lines point in the
direction of decreasing potential, higher potential is at B.
11. The electric potential is higher at point A. As with gravity, acceleration occurs in the direct of greatest
potential energy decrease.
12. The electric potential is higher at point A because the electron will move in the direction of the electric
field. The vector for the electric field is the negative of the of the potential.
13. Electric field lines point in the direction of decreasing electric potential. if it is released from rest and
starts moving, that means acceleration, which means there must be a force acting on the electron. The
field lines would be pointing from B to A, and since its moving from A to B, the electric potential will be
higher at B.
14. No.
15. to The potential is higher at point B, because E-field lines point from high potential to lower potential,
so the electron accelerates towards the higher potential.
Question 4: What (if any) are the conceptual and mathematical issues you are having difficulty
with from the reading?
1. As of now no, that may change once we start solving problems
2.
3. none
4.
5. None
6. I don't understand what the gradient is.
7. Continuity in electric potential and electric field
8. i'm a little confused on parts of the section of potential due to a sustem of point charges
9. none
10. None, really.
11. None
12.
13.
14. Why exactly is the electric field inside any conductor 0?
15. none
Question 5: What concerns or issues do you still have with material from previous classes?
1. Could you please go over discontinuity again, I am not quite sure how that works now.
2. I was having problems with integrating nonconducting spheres on the homework
3. none
4.
5. None
6. none
7. I don't remember any.
8.
9. none
10. I'm still confused on the problems with parallel surface charges on conductors.
11. None
12.
13.
14.
15. none