3B AP2 Electric Potential and Capacitors

A metal sphere with radius r1 has a total electric charge of magnitude q. An uncharged metal sphere with radius r2 (with r1 > r2) is then connected by a wire to the first sphere, as illustrated above. The separation of the spheres is much greater than the radius of either sphere. When equilibrium is reached, the spheres will have

• charges on their surfaces of equal magnitude and the same sign

• charges on their surfaces of equal magnitude and opposite sign

• equal electric fields at their surfaces

• equal capacitances

• equal electric potentials

A positive electric charge is moved at a constant speed between two locations in an electric field, with no work done by or against the field at any time during the motion. This situation can occur only if the

• charge is moved in the direction of the field

• charge is moved opposite to the direction of the field

• charge is moved perpendicular to an equipotential line

• charge is moved along an equipotential line

• electric field is uniform

A capacitor is constructed of two identical conducting plates parallel to each other and separated by a distance d. The capacitor is charged to a potential difference of V0 by a battery, which is then disconnected.

A sheet of insulating plastic material is inserted between the plates without otherwise disturbing the system. What effect does this have on the capacitance?

• It causes the capacitance to increase

• It causes the capacitance to decrease

• None; the capacitance does not change

• Nothing can be said about the effect without knowing the dielectric constant of the plastic

• Nothing can be said about the effect without knowing the thickness of the sheet.

A battery or batteries connected to two parallel plates produce the equipotential lines between the plates shown above.

The force on an electron located on the 0-volt potential line is

• 0 N

• 1 N, directed to the right

• 1 N, directed to the left

• directed to the right, but its magnitude cannot be determined without knowing the the distance between the lines

• directed to the left, but its magnitude cannot be determined without knowing the distance between the lines

If a dielectric is inserted between the plates of a capacitor while the capacitor maintains its connection to a constant voltage source, which of the following is true?

• The capacitance of the capacitor is unchanged

• The charge on the capacitor plates increases

• The potential difference across the capacitor increases

• The electric field between the capacitor plates increases

• The electric field between the capacitor plates decreases

A hollow conducting sphere is surrounded by a larger concentric spherical conducting shell, as shown above. The inner sphere has a net charge of –Q, and the outer sphere has a net charge of +3Q.

What is the net charge on the outer surface of the spherical shell?

• 0

• +Q

• +2Q

• +3Q

• +4Q

When two metal objects, X and Y, are connected to each other by a conducting wire, object X gains electrons. From this information, it can be inferred that before the connection was made, object X, compared with object Y, must have had

• less capacitance

• more electrical potential energy

• a smaller dielectric constant

• a greater electric charge

• a greater electric potential

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

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

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