Extended Response

True or false—Conservation of charge is like balancing a budget.

1. true
2. false

True or false—Although wood is an insulator, lightning can travel through a tree to reach Earth.

1. true
2. false

True or false—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.

1. true
2. false

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?

1. Because there are two types of charge, but only one type of mass exists.
2. Because there is only one type of charge, but two types of mass exist.
3. Because opposite charges cancel each other, while gravity does not cancel out.
4. 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. 1.02 × 10⁻⁷ N
2. 2.55 × 10⁻⁷ N
3. 5.1 × 10⁻⁷ N
4. 20.4 × 10⁻⁷ N

Point charges are located at each corner of a square with sides of 5.0 cm . The top-left charge is q₁ = 8.0 nC The top right charge is q₂ = 4.0 nC. The bottom-right charge is q₃ = 4.0 nC. The bottom-left charge is q₄ = 8.0 nC. What is the electric field at the point midway between charges q₂ and q₃?

1. $(–2.1\text{×}{10}^4 \text{N/C})\hat{x}$
2. $(2.3\text{×}{10}^4 \text{N/C})\hat{x}$
3. $(4.1\text{×}{10}^4 \text{N/C})\hat{x}$
4. $(4.6\text{×}{10}^4 \text{N/C})\hat{x}$

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.

1. Take the wire on the x-axis, and draw electric-field lines perpendicular to it.
2. Take the wire on the x-axis, and draw electric-field lines parallel to it.
3. Take the wire on the y-axis, and draw electric-field lines along it.
4. Take the wire on the z-axis, and draw electric-field lines along it.

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. 1.3 × 10⁻⁶ J
2. 2.5 × 10⁻⁶ J
3. 3.8 × 10⁻⁶ J
4. 5.1 × 10⁻⁶ J

How are potential difference and electric-field strength related for a constant electric field?

1. The magnitude of electric-field strength is equivalent to the potential divided by the distance.
2. The magnitude of electric-field strength is equivalent to the product of the electric potential and the distance.
3. The magnitude of electric-field strength is equivalent to the difference between magnitude of the electric potential and the distance.
4. The magnitude of electric-field strength is equivalent to the sum of the magnitude of the electric potential and the distance.

A 12 μF air-filled capacitor has 12 V across it. If the surface charge on each capacitor plate is σ = 7.2 mC / m², what is the attractive force of one capacitor plate toward the other?

1. 0.81 × 10⁵ N
2. 0.81 × 10⁶ N
3. 1.2 × 10⁵ N
4. 1.2 × 10⁶ N

Explain why capacitance should be inversely proportional to the separation between the plates of a capacitor.

1. Capacitance is directly proportional to the electric field, which is inversely proportional to the distance between the capacitor plates.
2. Capacitance is inversely proportional to the electric field, which is inversely proportional to the distance between the capacitor plates.
3. Capacitance is inversely proportional to the electric field, which is directly proportional to the distance between the capacitor plates.
4. Capacitance is directly proportional to the electric field, which is directly proportional to the distance between the capacitor plates.