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15 Kirchoff's Laws

10 consider a 150w passive element that operates at

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Unformatted text preview: ) Then the energy consumed between the times t1 and t2 is given by: t E 2 p(t )dt t1 Example 2: (Alan 1.10) Consider a 150W passive element that operates at 120V dc voltage. How many electrons flow through this element in 1h? Ans: Since we have a dc case: P V0 I0 P 150 I0 1.25A V0 120 Within 1h, this current transports 1.25 × 3600 = 4500 C (BE CAREFUL TO ALWAYS USE SI UNITS! Secs not h!) Thus the number of electrons is: # electrons = 4500 1.602 10 ‐19 = 28.09 1021 Voltage and Current Sources Sources are active elements that generate electric power. They do this by converting some other energy form to electric energy. For example, batteries rely on chemical reactions to generate electric power. 15.4 While no ideal sources exist, some practical sources come pretty close to an ideal source. But what is an ideal source? We have two different case: • Ideal voltage source: a device that maintains a voltage v(t) across its terminals regardless of what is connected to it (i.e. regardless of how much current is being drawn from the source). • Ideal current source: a device that supplies a current i(t) regardless of the voltage across its terminals. Sources are also divided into independent and dependent. The output of an independent source is not a function of any current or voltage of the circuit it is connected to. On the other hand, the output of a dependent source is a function of some current or voltage of the circuit. Examples: 1. Batteries are often approximated as ideal, independent voltage sources Notice that the current on a source does not...
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