posted by .

potential difference=40v b2n plate A & B.
find work done if q=+3C from
a) B to A
b) A to B

*i already know the ans but i need the explanation for the formula.

-this is my work
a)w=-qv b)-120J
=120 J

what i want to ask is:
1-why must we add - sign for v is not that if the v is against electric field is +?

  • physics -

    You don't say whether A or B has the higher potential. You only say that the difference "between" them is 40 V.

    If a positive charge moves to a higher potential, the potential energy increases. The E field and force is opposite to the direction of motion in that situation.

  • phy -

    i'm sorry. the electric field are from A to B.

    dear drwls,you didn't answer my question.
    i know about the concept but why the v is negative? or how can it be proven mathematically by the formula?.

  • phy -

    Start with the definition of work
    Work=Force dot distance
    = Eq dot distance
    but E=-dV/dx by definition of direction of E field. E goes from + V to -V (the direction of a pos test charge)
    Work= q*-dV/dx dot distance
    work= -q dV/dx dot dx

    Now, if the distance is in the direction of the gradient, then
    work=-q DeltaV

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. physics

    The plates of a parallel plate capacitor each have an area of 0.40 m2 and are separated by a distance of 0.02 m. They are charged until the potential difference between the plates is 3000 V. The charged capacitor is then isolated. …
  2. Physics

    I never learned how to do these... An electron moves from one plate of a capaci- tor to another, through a potential difference of 2495 V. a) Find the speed with which the electron strikes the positive plate. Answer in units of m/s. …
  3. physics

    An electron moves from one plate to another across which there is a potential difference of 2000 V. a) Find the speed with which the electron strikes the positive plate. For this problem, I used the Potential difference equation: (2000)(1.60x10^-19)=3.2E-16=delta …
  4. Physics

    An electron enters a parallel plate apparatus 10.0cm long and 2.0cm wide, moving horizontally at 8.0 × 10^7 m/s. (top plate is positive, electron is 1.0cm from each plate..) The potential difference between the plates is 6.0 × 10^2 …
  5. physics

    1)The difference of potential between terminals of a battery is 6V. How much work is done when a series of negative charges totaling 0.5 C are moved from one terminal to another?
  6. Physics

    Thank you for answering my previous questions! I have another one now in regards to the following question... An unknown potential difference exists between the inner and outer surfaces of the membrane of a cell. The inner surface …
  7. physics

    The physics of an electron moving from one plate to another. An electron acquires 4.2 x 10-16 J of kinetic energy when it is accelerated by an electric field from Plate A to Plate B. What is the potential difference between the plates, …
  8. physics

    If 180 J of work is performed to move four coulombs of charge from the positive plate to the negative plate shown below, what potential difference exists between the plates?
  9. Physics

    Right now in physics we are learning about electric potential energy and electric potential. My question is: P and Q are points within a uniform electric field that are separated by a distance of 0.1 m. The potential difference between …
  10. Physics Capacitance

    Three uncharged capacitors, X, Y, Z, each with capacitance of 12uF each are connected A---------[X]------[Y/Z]-----------B *Y&Z is parallel to each other* A potential difference of 9.0V is applied between points A and B. Explain why …

More Similar Questions