Extended Response
18.1 Electrical Charges, Conservation of Charge, and Transfer of Charge

Many macroscopic objects would be charged, so we would experience the enormous force of electricity on a daily basis.

Many macroscopic objects would be charged, so we would experience the small force of electricity on a daily basis.

Many macroscopic objects would be charged, but it would not affect life on Earth and physics in general.

Macroscopic objects would remain neutral, so it would not affect life on Earth and physics in general.
True or falseâ€”Conservation of charge is like balancing a budget.
 true
 false
True or falseâ€”Although wood is an insulator, lightning can travel through a tree to reach Earth.
 true
 false
True or falseâ€”An eccentric inventor attempts to levitate by first placing a large negative charge on himself and then putting a large positive charge on the ceiling of his workshop. Instead, while he attempts to place a large negative charge on himself, his clothes fly off.
 true
 false
18.2 Coulomb's law
Electrostatic forces are enormous compared to gravitational force. Why do you not notice electrostatic forces in everyday life, whereas you do notice the force due to gravity?
 Because there are two types of charge, but only one type of mass exists.
 Because there is only one type of charge, but two types of mass exist.
 Because opposite charges cancel each other, while gravity does not cancel out.
 Because opposite charges do not cancel each other, while gravity cancels out.
A small metal sphere with a net charge of 3.0 nC is touched to a second small metal sphere that is initially neutral. The spheres are then placed 20 cm apart. What is the force between the spheres?
 1.02 Ã— 10^{âˆ’7} N
 2.55 Ã— 10^{âˆ’7} N
 5.1 Ã— 10^{âˆ’7} N
 20.4 Ã— 10^{âˆ’7} N
18.3 Electric Field
Point charges are located at each corner of a square with sides of 5.0 cm . The topleft charge is q_{1} = 8.0 nC The top right charge is q_{2} = 4.0 nC. The bottomright charge is q_{3} = 4.0 nC. The bottomleft charge is q_{4} = 8.0 nC. What is the electric field at the point midway between charges q_{2} and q_{3}?
 $(\xe2\u20ac\u201c2.1\phantom{\rule{0.25em}{0ex}}\text{\xc3\u2014}\phantom{\rule{0.25em}{0ex}}{10}^{4}\text{N/C})\hat{x}$
 $(2.3\phantom{\rule{0.25em}{0ex}}\text{\xc3\u2014}\phantom{\rule{0.25em}{0ex}}{10}^{4}\text{N/C})\hat{x}$
 $(4.1\phantom{\rule{0.25em}{0ex}}\text{\xc3\u2014}\phantom{\rule{0.25em}{0ex}}{10}^{4}\text{N/C})\hat{x}$
 $(4.6\phantom{\rule{0.25em}{0ex}}\text{\xc3\u2014}\phantom{\rule{0.25em}{0ex}}{10}^{4}\text{N/C})\hat{x}$
A long straight wire carries a uniform positive charge distribution. Draw the electric field lines in a plane containing the wire at a location far from the ends of the wire. Do not worry about the magnitude of the charge on the wire.
 Take the wire on the xaxis, and draw electricfield lines perpendicular to it.
 Take the wire on the xaxis, and draw electricfield lines parallel to it.
 Take the wire on the yaxis, and draw electricfield lines along it.
 Take the wire on the zaxis, and draw electricfield lines along it.
18.4 Electric Potential
A square grid has charges of Q = 10 nC are each corner. The sides of the square at 10 cm . How much energy does it require to bring a q = 1.0 nC charge from very far away to the point at the center of this square?
 1.3 Ã— 10^{âˆ’6} J
 2.5 Ã— 10^{âˆ’6} J
 3.8 Ã— 10^{âˆ’6} J
 5.1 Ã— 10^{âˆ’6} J
How are potential difference and electricfield strength related for a constant electric field?
 The magnitude of electricfield strength is equivalent to the potential divided by the distance.
 The magnitude of electricfield strength is equivalent to the product of the electric potential and the distance.
 The magnitude of electricfield strength is equivalent to the difference between magnitude of the electric potential and the distance.
 The magnitude of electricfield strength is equivalent to the sum of the magnitude of the electric potential and the distance.
18.5 Capacitors and Dielectrics
A 12 Î¼F airfilled capacitor has 12 V across it. If the surface charge on each capacitor plate is Ïƒ = 7.2 mC / m^{2}, what is the attractive force of one capacitor plate toward the other?
 0.81 Ã— 10^{5} N
 0.81 Ã— 10^{6} N
 1.2 Ã— 10^{5} N
 1.2 Ã— 10^{6} N
Explain why capacitance should be inversely proportional to the separation between the plates of a capacitor.
 Capacitance is directly proportional to the electric field, which is inversely proportional to the distance between the capacitor plates.
 Capacitance is inversely proportional to the electric field, which is inversely proportional to the distance between the capacitor plates.
 Capacitance is inversely proportional to the electric field, which is directly proportional to the distance between the capacitor plates.
 Capacitance is directly proportional to the electric field, which is directly proportional to the distance between the capacitor plates.