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**20.1 Schematic Diagrams and Circuits**

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Essential Questions How does the wiring in a circuit change its ability to supply power to devices? How do we represent physical circuit elements in schematic drawings?

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**Objective(s): We will be able to…**

Interpret and construct circuit diagrams. Identify circuits as open or closed. Deduce the potential difference across the circuit load, given the potential difference across the battery’s terminals.

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**Agenda: Warm-Up Recap what happened on Friday.**

Reminder: Chapter 19 Test Tomorrow. Introduction to Circuit Diagrams Notes: Schematic Diagrams Circuits and short circuits EMFs

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Warm Up The following drawings are used in circuit diagrams. List what you think each object represents. Battery/DC Source Switch Capacitor Wire Resistor Light Bulb Plug

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Schematic Diagrams A diagram that is used to represent the construction of an electrical apparatus is a schematic diagram. Sometimes called a circuit diagram. They are used to determine how parts in an electrical device are arranged, and to help understand how they work.

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**Schematic Diagram Symbols**

Wire or conductor

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**Schematic Diagram Symbols**

Resistor or circuit load (Overall resistance. Discussed more in a minute.)

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**Schematic Diagram Symbols**

Bulb or lamp

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**Schematic Diagram Symbols**

Plug

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**Schematic Diagram Symbols**

Battery

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**Schematic Diagram Symbols**

Switch

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**Schematic Diagram Symbols**

Capacitor

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Electric Circuits An electric circuit is a pathway through which charges can be conducted. Circuits (and switches) must be closed to complete the pathway, otherwise charges will not flow. Light switch on. Open circuits conduct no electricity. Light switch off.

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**Electrical Circuits All circuits consist of two things…**

A source of potential difference (electrical energy), like a battery, and… A load: an element or group of elements in a circuit that dissipates energy.

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Light Bulbs Light bulbs themselves are a complete circuit with a resistor. The filament acts as a resistor, converting electrical energy into internal energy and thus heat and light.

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Short Circuits Without a load (bulb or resistor), a circuit has very little resistance. And therefore, very high current. This is called a short circuit. Most wires overheat when they short circuit (think of the battery and the paperclip). DANGEROUS! This is why we have fuses and circuit breakers.

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**Electromotive Force (emf)**

Literally, the force that moves electrons. Any device that increases the flow of charge in a circuit is a source of emf, the energy per unit charge supplied by the source. In real life, the terminal voltage (actual potential difference from the battery) is less than its emf due to internal resistance. The amount of power the battery actually supplies is less than what it should, because some of the energy is wasted internally.

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Terminal Voltage The potential difference across a load equals the terminal voltage. Meaning: if a battery supplies 1.5 volts of potential difference, then the voltage across the resistor, bulb, or collection of resistors and bulbs etc. is 1.5 volts. No energy created or destroyed.

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Recap Circuit diagrams are used to represent and analyze the composition of electric devices. Open circuits do not have a complete pathway, so they do not conduct electricity. Closed circuits complete the pathway, so they do conduct electricity. The voltage across the load of a circuit is the same as the voltage supplied by the battery.

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Homework Tonight: Finish study guide. Due Wed: p 735 #1-5

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