Electric Potential and Equipotential Surfaces.

Two negative point charges are a distance 𝑥 apart

and have potential energy 𝑈. If the distance between

the point charges increases to 3𝑥, what is their new

potential energy?

• 9𝑈

• 3𝑈

• 𝑈

• 𝑈/3

• 𝑈/9

A negative 5 μ𝐶 charge is located 0.5 m from a positive 10 μ𝐶 charge as shown below. At how many positions (excluding infinity) on a line passing through both charges is the electric potential equal to zero?

• 0

• 1

• 2

• 3

Two, point charges, 𝑄1 = +3μ𝐶 and 𝑄2 = −3μ𝐶, are situated as shown in the figure below. Which point has the lowest potential?

• A

• B

• C

• D

• E

In the figure below, two small spheres, each with charge + Q, are fixed in place at the corners of an equilateral triangle. Point I is at the third corner, and point II is midway between the charges.

A small particle with charge +q where 𝑞 << 𝑄, is moved from point I to point II at constant speed 𝑣 by an external force. Wext is the work done by the external force on the moving charge, and Welec( is the work done by the electrostatic force. Which of the following correctly identifies the signs of these quantities?

• Wext + Welec -

• Wext + Welec +

• Wext - Welec -

The point with higher potential is

• I

• II

The unit (units) of electric field:

• V/m

• N/C

• J/C

• N/V

The highest electric field is at the point

• A

• B

• C

• D

The two points in the figure, in which a positive charge can move between them due to electric force only. Are:

• D to B

• C to A

• A to B

• B to D

V= 3x^2

the electric field is:

• -6x

• 6x

• -x^3

• x^3

In which cases (points) the electric potential (V) = 0

• When there are no charges in the region.

• At Infinity. (r= Infinity)

• At a point near + and - charges and their potential cancel each other

• At the midpoint of 2 positive charges.