University Physics Volume 2

# Conceptual Questions

University Physics Volume 2Conceptual Questions

### 8.1Capacitors and Capacitance

1.

Does the capacitance of a device depend on the applied voltage? Does the capacitance of a device depend on the charge residing on it?

2.

Would you place the plates of a parallel-plate capacitor closer together or farther apart to increase their capacitance?

3.

The value of the capacitance is zero if the plates are not charged. True or false?

4.

If the plates of a capacitor have different areas, will they acquire the same charge when the capacitor is connected across a battery?

5.

Does the capacitance of a spherical capacitor depend on which sphere is charged positively or negatively?

### 8.2Capacitors in Series and in Parallel

6.

If you wish to store a large amount of charge in a capacitor bank, would you connect capacitors in series or in parallel? Explain.

7.

What is the maximum capacitance you can get by connecting three $1.0-μF1.0-μF$ capacitors? What is the minimum capacitance?

### 8.3Energy Stored in a Capacitor

8.

If you wish to store a large amount of energy in a capacitor bank, would you connect capacitors in series or parallel? Explain.

### 8.4Capacitor with a Dielectric

9.

Discuss what would happen if a conducting slab rather than a dielectric were inserted into the gap between the capacitor plates.

10.

Discuss how the energy stored in an empty but charged capacitor changes when a dielectric is inserted if (a) the capacitor is isolated so that its charge does not change; (b) the capacitor remains connected to a battery so that the potential difference between its plates does not change.

### 8.5Molecular Model of a Dielectric

11.

Distinguish between dielectric strength and dielectric constant.

12.

Water is a good solvent because it has a high dielectric constant. Explain.

13.

Water has a high dielectric constant. Explain why it is then not used as a dielectric material in capacitors.

14.

Elaborate on why molecules in a dielectric material experience net forces on them in a non-uniform electrical field but not in a uniform field.

15.

Explain why the dielectric constant of a substance containing permanent molecular electric dipoles decreases with increasing temperature.

16.

Give a reason why a dielectric material increases capacitance compared with what it would be with air between the plates of a capacitor. How does a dielectric material also allow a greater voltage to be applied to a capacitor? (The dielectric thus increases C and permits a greater V.)

17.

Elaborate on the way in which the polar character of water molecules helps to explain water’s relatively large dielectric constant.

18.

Sparks will occur between the plates of an air-filled capacitor at a lower voltage when the air is humid than when it is dry. Discuss why, considering the polar character of water molecules.

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