2.3 Consiiuction ofa Cncuit llodetConstructing a Circuit Modet of a FtashtightConsrruct a circuit model oia flashlight. SoLution We chose the flashlighl to illustrate a practical system because its components are so familar. Figure 2.9 shows a photograph of a widely available flashlight. When a flashlight is regarded as an electrical system, the components of primary interest are the batteries, the lamp, the connector, the case, and theswitch. We now consider the circuit model for each A dry-cell battery maintahs a reasonably con- start teminal voltage if the current demand is rot excessive. Thus if the dry-cell battery is opemting witlin its intended limitq we can model it wrth an ideal voltage source. The prescribed voltage ther is constant and equal to the sum of two dry-cell value$ The ultimate output of the lamp is light energy,which is achieved by heating the filament in thelamp to a tempeiature high enough to cause
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