0195136047.pdf

52 CIRCUIT CONCEPTS

TABLE 1.5.3Analogy Between Thermal and Electrical Systems

Thermal System Electrical System

Heat Charge

Heat flow Current

Temperature difference Voltage

Ambient temperature Ground reference

Heat capacity Capacitance

Thermal resistance Electrical resistance

Heat flow ∼=

k

x

T (1.5.1)

wherekis a constant, andk/xin thermal systems is analogous to conductance in electrical

systems. Then Newton’s law of cooling, in a very simplified form, can be seen to be a thermal

version of Ohm’s law.

1.6 Learning Objectives

Thelearning objectivesof this chapter are summarized here, so that the student can check whether

he or she has accomplished each of the following.

• Review of basic electrical quantities.


• Application of Coulomb’s law, Ampere’s law, and the Biot–Savart law.


• Energy and power computations in a circuit consisting of a source and a load.


• Calculation of average and RMS values for periodic waveforms, and time constant for
  exponential waveforms.


• i–vrelationships for ideal resistors, capacitors, and inductors; duality principle.


• Reduction of series and parallel combinations of resistors, capacitors, and inductors.


• Solution of simple voltage and current divider circuits.


• Computation of power absorbed by a resistor, and energy stored in a capacitor or inductor.


• Maximum power transfer and matched load.


• Volt-ampere equations and energy stored in coupled inductors.


• Ideal transformer and its properties.


• Application of Kirchhoff’s current and voltage laws to circuits.


• Measurement of basic electrical parameters.


• Analogy between electrical and other nonelectric physical systems.

1.7 PRACTICAL APPLICATION: A CASE STUDY

Resistance Strain Gauge

Mechanical and civil engineers routinely employ the dependence of resistance on the physical

dimensions of a conductor to measure strain. A strain gauge is a device that is bonded to the

surface of an object, and whose resistance varies as a function of the surface strain experienced

by the object. Strain gauges can be used to measure strain, stress, force, torque, and pressure.