AP Physics

Two charged particles, 𝑄1 = + 12.0 𝑚𝐶 and 𝑄2 = −5.0𝑚𝐶 are placed on a line. At what finite locations along the line may the electric potential be equal to zero?
I.  in between the particles, closer to the positive particle
II.  in between the particles, closer to the negative particle III.  not in between, but closer to the positive particle
IV.  not in between, but closer to the negative particle

• I only 
• II only   
• IV only     
•  II and IV only

The electric field in a region of space is given by the function 𝐸 = −30𝑥 + 2, where 𝑥 is in meters and 𝐸 is in volts/meter. What is the electric potential at 𝑥  = 2𝑚, relative to the origin?

• +56 V
• +60 V
• –30 V
• –56 V

The diagram shows a very long, thin wire that carries a charge per unit length 𝜆. A Gaussian cylinder is imagined with its axis along the line and having radius 𝑎. the length of the Gaussian cylinder is 𝐿. How much charge is enclosed in this cylinder?

• 𝑄_enc = 2𝜋𝜆𝑎𝐿
• 𝑄_enc = 𝜋𝜆𝑎𝐿
• 𝑄_enc =𝜆𝐿
• 𝑄_enc = 2𝜋𝜆𝑎²𝐿

Three equal point charges +𝑞 are placed at the vertices of an equilateral triangle of side length 𝑎. calculate the potential at the center of the triangle at 𝑃.

• 3√3𝑄/ 2𝜋𝜀_o𝑎
• 3√3𝑄/ 4𝜋𝜀_o𝑎
• √3𝑄/ 2𝜋𝜀_o𝑎
• 3𝑄/ 2𝜋𝜀_o𝑎

A light, rigid, insulating rod of length L is free to rotate vertically about a horizontal axis at one end. At the other end of the rod, a charged sphere of mass m and charge –Q is mounted. The rod is released in a horizontal position as shown above while an electric field is applied in the vicinity of the sphere. What magnitude and direction of the field is required to maintain the sphere-rod in the horizontal orientation?

•     𝑚𝑔 /𝑄, up
•  𝑚𝑔 /𝑄, down
•  𝑚𝑔L /𝑄, up
•  𝑚𝑔L /𝑄, down

For the set up shown, which statement concerning the point P is true?

• The potential is zero and the field is to the right.
• The potential is zero and the field is to the left   
• The potential is negative and the field is zero   
• The potential is positive and the field is zero

The graph in the figure shows the variation of the electric potential 𝑉(𝑥) (in arbitrary units) as a function of the position 𝑥 (also in arbitrary units). Which of the choices below correctly describes the orientation of the x-component of the electric field along the 𝑥 −axis?

• 𝐸_k is positive from 𝑥 = −2 𝑡𝑜 𝑥 =  2 
• 𝐸_k is negative from 𝑥 = −2 𝑡𝑜 𝑥 = 2 
• 𝐸_k is positive from 𝑥 = −2 𝑡𝑜 𝑥 = 0, and negative from 𝑥 = 0 𝑡𝑜 𝑥 = 2 
• 𝐸_k is negative from 𝑥 = −2 𝑡𝑜 𝑥 = 0, and positive from 𝑥 = 0 𝑡𝑜 𝑥 = 2

The net flux through a Gaussian surface is zero. Which of the following statements must be true?
I.  There are no charges inside the surface
II.  The net charge inside the surface is zero
III.  The electric field everywhere on the surface is zero
IV.  The number of electric field lines entering the surface equals that leaving the surface

• I only 
• II only
• II and III only 
• II and IV only

Three charges of −2.00µ𝐶, +4.00µ𝐶 𝑎𝑛𝑑 + 6.00µ𝐶 are placed along the 𝑥 −axis as shown in the figure. What is the electrical potential at point P (relative to infinity) due to these charges?

• 0 𝑘𝑉 
• −154 𝑘𝑉 
• −307 𝑘𝑉 
• +307 𝑘𝑉

Determine the electric filed at point P from the two point charges both of charge +𝑄, with one point charge being a distance 𝑅 and the other being a distance 2𝑅.

• 3𝑞 /16𝜋𝜀_o𝑅²
  
• 2𝑞 /16𝜋𝜀_o𝑅²
• 3𝑞 /4𝜋𝜀_o𝑅²
• 2𝑞 /4𝜋𝜀_o𝑅²