 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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