1.9 Summary

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1.9 Summary

• 1. An electric circuit consists of electrical elements connected together.
• 2. The International System of Units (SI) is the international mea surement language, which enables engineers to communicate their results. From the se ven principal units, the units of other ph ysical quantities can be derived.

3. Current is the rate of char ge flow past a gi ven point in a gi ven direction.

$$i = \frac{dq}{dt}$$

4. Voltage is the energy required to move 1 C of char ge from a reference point (−) to another point (+).

vab = ___ dw dq

5. Power is the energy supplied or absorbed per unit time. It is also the product of voltage and current.

$$p = \frac{dw}{dt} = vi$$

• 6. According to the passi ve sign con vention, power assumes a posi tive sign when the current enters the positive polarity of the voltage across an element.
• 7. An ideal v oltage source produces a specific potential difference across its terminals re gardless of what is connected to it. An ideal current source produces a specific current through its terminals regardless of what is connected to it.
• 8. Voltage and current sources can be dependent or independent. A dependent source is one whose value depends on some other circuit variable.
• 9. Two areas of application of the concepts covered in this chapter are the TV picture tube and electricity billing procedure.

Review Questions

1.1 One millivolt is one millionth of a volt.

(a) True (b) False

1.2 The prefix micro stands for:

(a) 10⁶ (b) 103 (c) 10⁻³ (d) 10⁻⁶

1.3 The voltage 2,000,000 V can be expressed in powers of 10 as:

(a) 2 mV (b) 2 kV (c) 2 MV (d) 2 GV

1.4 A charge of 2 C flowing past a given point each second is a current of 2 A.

(a) True (b) False

1.5 The unit of current is:

(a) coulomb (b) ampere (c) volt (d) joule

1.6 Voltage is measured in:

(a) watts (b) amperes

(a) True (b) False

• (c) volts (d) joules per second
• 1.7 A 4-A current charging a dielectric material will accumulate a charge of 24 C after 6 s.

1.8 The voltage across a 1.1-kW toaster that produces a current of 10 A is:

(a) 11 kV (b) 1100 V (c) 110 V (d) 11 V

1.9 Which of these is not an electrical quantity?

(a) charge	(b) time	(c) voltage
(d) current	(e) power

• 1.10 The dependent source in Fig. 1.22 is:
  • (a) voltage-controlled current source
  • (b) voltage-controlled voltage source
  • (c) current-controlled voltage source
  • (d) current-controlled current source

Figure 1.22 For Review Question 1.10.

Answers: 1.1b, 1.2d, 1.3c, 1.4a, 1.5b, 1.6c, 1.7a, 1.8c, 1.9b, 1.10d.