Critical Thinking Items

If you dive into a pool of seawater through which an equal amount of positively and negatively charged particles is moving, will you receive an electric shock?

1. Yes, because negatively charged particles are moving.
2. No, because positively charged particles are moving.
3. Yes, because positively and negatively charged particles are moving.
4. No, because equal amounts of positively and negatively charged particles are moving.

True or false—The high-voltage wires that you see connected to tall metal-frame towers are held aloft by insulating connectors, and these wires are wrapped in an insulating material.

1. true
2. false

By considering the molecules of an insulator, explain how an insulator can be overall neutral but carry a surface charge when polarized.

1. Inside the insulator, the oppositely charged ends of the molecules cancel each other.
2. Inside the insulator, the oppositely charged ends of the molecules do not cancel each other.
3. The electron distribution in all the molecules shifts in every possible direction, leaving an excess of positive charge on the opposite end of each molecule.
4. The electron distribution in all the molecules shifts in a given direction, leaving an excess of negative charge on the opposite end of each molecule.

In terms of Coulomb’s law, why are water molecules attracted by positive and negative charges?

1. Water molecules are neutral.
2. Water molecules have a third type of charge that is attracted by positive as well as negative charges.
3. Water molecules are polar.
4. Water molecule have either an excess of electrons or an excess of protons.

An arbitrary electric field passes through a box-shaped volume. There are no charges in the box. If 11 electric-field lines enter the box, how many electric-field lines must exit the box?

1. nine electric field lines
2. 10 electric field lines
3. 11 electric field lines
4. 12 electric field lines

In a science-fiction movie, a villain emits a radial electric field to repulse the hero. Knowing that the hero is electrically neutral, is this possible? Explain your reasoning.

1. No, because an electrically neutral body cannot be repelled or attracted.
2. No, because an electrically neutral body can be attracted but not repelled.
3. Yes, because an electrically neutral body can be repelled or attracted.
4. Yes, because an electrically neutral body can be repelled.

What is the relationship between voltage and energy? More precisely, what is the relationship between potential difference and electric potential?

1. Voltage is the energy per unit mass at some point in space.
2. Voltage is the energy per unit length in space.
3. Voltage is the energy per unit charge at some point in space.
4. Voltage is the energy per unit area in space.

Three parallel plates are stacked above each other, with a separation between each plate. If the potential difference between the first two plates is ΔV₁ and the potential between the second two plates is ΔV₂, what is the potential difference between the first and the third plates?

1. ΔV₃ = ΔV₂ + ΔV₁
2. ΔV₃ = ΔV₂ − ΔV₁
3. ΔV₃ = ΔV₂ / ΔV₁
4. ΔV₃ = ΔV₂×ΔV₁

When you insert a dielectric into a capacitor that has been charged and then disconnected from the charging battery, the energy stored in the capacitor decreases. If you take the dielectric out, the energy increases again. Where does this energy go in the former case, and where does the energy come from in the latter case?

1. Energy is released by the dielectric when it is introduced between the plates and then reabsorbed when it is removed.
2. The energy goes into polarizing the dielectric when it is added. When you remove the dielectric, energy comes from your work pulling on the dielectric.
3. Energy goes into you when you insert the dielectric, and comes from you when you remove it.
4. Energy is released to polarize the dielectric when it is introduced between the plates. The polarized dielectric transfers the energy back into the capacitor when the dielectric is removed.