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Circuit Elements

There are 5 ideal basic circuit elements:

a. Voltage sourcesb. Current sourcesc. Resistorsd. Capacitorse. Inductors

Our goal in this chapter is to be able to solve difficult problems by using simplifying models.

1. An electric source is a device that is capable of converting nonelectric energy to electricalenergy and vice versa.

2. Ideal sources are examples of active circuit elements. Active elements are used to modeldevices that are capable of generating electrical energy.

3. Passive elements are used model physical devices that are not capable of generatingelectrical energy.4. Independent source and dependent sources supply the same current through a pair ofterminals in the same reference direction.

5. Resistance is the capacity of materials to impede the flow of current or move specifically,the flow of electric charge.

6. A resistor is the circuit element that is used to model this behavior.7. For the purposes of circuit analysis, we must reference the current in the resistor to the

terminal voltage.

8. The resistance of an ideal resistor is constant and its value does not vary over time.Constructing a Circuit Model of a Flashlight:

9. One reason for an interest in the basic circuit elements is that they can be used toconstruct circuit models of practical systems.

10.If the switch is ON, a Resistor has zero resistance (R=0).11.If the switch is OFF, a Resistor has an infinite resistance (R= Infinity).12.The heat resulting from resistance in a lamp produces light, which is a desire effect.13.Two more algebraic relationships, known as Kirchhoffs Laws are used to solve most

circuits.

14.A node is a point where 2 or more circuits elements meet.15.The idea of using circuit elements to model practical electronic components requires

approximation.

16.A circuit is said to be solved when the voltage across its sources and the current in everyelement is determined.

Kirchhoffs Current Law

The algebraic sum of all currents at a given node in a circuit equals zero (KCL) ----- eqn 1.

Kirchhoffs Voltage Law

The algebraic sum of all voltages in a closed loop equals zero (KVL) ----- eqn 2.

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Practical Perspectives:

To allow us to predict and control electrical phenomena, we use simplifying models in which

simple mathematical relationships between voltage and current approximate the actual

relationships in real objects.

a. An ideal voltage source maintains a prescribed voltage across its terminals regardless ofthe current flowing in those terminals.

b. An ideal current source maintains a prescribed current across its terminals regardless ofthe voltage across its terminals.

c. An independent source establishes a voltage or current in a circuit without relying onvoltages or currents elsewhere in the circuit.

d. An active element is one that models a device capable of generating electric energy.e. Passive elements are used to model physical devices that cannot generate electric energy.