Parts of An Electric Circuit Recall: a circuit is a closed path Electric circuit: closed path that flowing charge follows Constructing an electric circuit: Three key components needed: “Source”: a source of voltage or current Component: a device that requires electrical energy Connectors: something to connect source to component Images obtained from:

Circuit Diagrams Circuit diagram: standardized method of illustrating the parts of a circuit Components, sources have specific symbols Many components– what we’ll use is the tip of the iceberg Image obtained from:

Circuit Sources Battery Provides potential difference for circuit Electrons will flow from high voltage to low voltage in circuit Positive end Negative end + -

Circuit Components Switch Controls path of current within circuit On: ends of switch connected, closes circuit Off: ends of switch not connected, circuit open

Circuit Components Resistor Creates resistance in circuit Serve to reduce amount of voltage remaining in circuit Causes energy to be released from it– often thermal energy Example: incandescent light bulb

Circuit Components Rheostat/Potentiometer Variable resistor: can change its resistance

As You Come In… Find the voltage drop in this part of a circuit: 5.0 Ω 0.15 A

Circuit Components Capacitor Stores charge in the circuit Acts like temporary battery Builds up charge when connected to source until full Discharges charge when disconnected from source until empty

Circuit Components Inductor Resists changes in current If connected to source, keeps current from flowing for a while If disconnected from source, keeps current flowing for a while (how???)

Circuit Components Ammeter Measures current running through part of circuit A

Circuit Components Voltmeter Measures voltage running through part of circuit V

Circuit Components Generic Device Appliance or general electrical device that is part of circuit Name

Circuit Connectors Conductor/wire Connects sources, components Assumed to have negligible resistance Junctions Sometimes connectors cross paths or intersect Node: conductors connect No node: conductors do not connect Node No node

Circuit Connectors Ground Connects circuit to “ground” “Ground” has electrical potential of 0 V Prevents short circuits– more on those later!

Circuit Diagrams: Determining Current Given the following circuit diagram: Want to know I Magnitude of I is simple: R = V / I I = V / R What about direction? Electron flow notation: electrons flow from (-) to (+) of a voltage source Current flowing CCW 3.0 Ω 1.5 V - + I = 0.50 A = 0.50 A

Circuit Diagrams: Series Circuits Given the following circuit diagram: Resistors are in a series– one after another along one path Called a “series circuit” R 2 = 3.0 Ω 1.5 V R 1 = 5.0 Ω R 3 = 1.0 Ω

Circuit Diagrams: Series Circuits What do we know about circuit? Only one path for electrons to flow Current through each resistor must be the same I 1 = I 2 = I 3 Voltage drop by end of path must equal voltage of source V 1 + V 2 + V 3 = V total R 2 = 3.0 Ω 1.5 V R 1 = 5.0 Ω R 3 = 1.0 Ω

Circuit Diagrams: Series Circuits R 2 = 3.0 Ω 1.5 V R 1 = 5.0 Ω R 3 = 1.0 Ω = I

Circuit Diagrams: Series Circuits R total = 9.0 Ω 1.5 V Equivalent Circuit = I

Circuit Diagrams: Series Circuits R total = 9.0 Ω 1.5 V Equivalent Circuit = I

Practice Problem: Series Circuit R 2 = ? 6.0 V R 1 = 1.5 Ω 3.0 A = 2.0 Ω

About Series Circuits Advantages: Easy to set up (cheap) Batteries in series: voltages additive, increases current Less connectors needed Disadvantages: Voltage divided between components– more components, less voltage for each One path for current– if one component fails, circuit fails Resistance increases– decreases current within circuit R 2 = 3.0 Ω 1.5 V R 1 = 5.0 Ω R 3 = 1.0 Ω

Circuit Diagrams: Parallel Circuits Given the following circuit diagram: Resistors along multiple, different, parallel paths Called a “parallel circuit” 1.5 V R 1 = 5.0 Ω R 2 = 3.0 Ω R 3 = 1.0 Ω

Circuit Diagrams: Parallel Circuits What do we know about circuit? Multiple paths for e - to flow Total current of circuit equal to current through each resistor I 1 + I 2 + I 3 = I total Voltage drop the same across each resistor– equals voltage of source V 1 = V 2 = V 3 = V total 1.5 V R 1 = 5.0 Ω R 2 = 3.0 Ω R 3 = 1.0 Ω

Circuit Diagrams: Parallel Circuits 1.5 V R 1 = 5.0 Ω R 2 = 3.0 Ω R 3 = 1.0 Ω = V

Circuit Diagrams: Parallel Circuits 1.5 V R total = 1.8 Ω Equivalent Circuit = V

Practice Problem: Parallel Circuit 6.0 V R 1 = 15 Ω R 2 = 5.0 Ω R 3 = 7.5 Ω ??? = 6.0 V / 2.5 Ω = 2.4 A

About Parallel Circuits 1.5 V R 1 = 5.0 Ω R 2 = 3.0 Ω R 3 = 1.0 Ω Advantages: Voltage the same across each component Total resistance decreases compared to each component’s resistance Batteries in parallel make batteries last longer Multiple paths for current– can be redirected if one part of circuit fails Disadvantages: More connectors needed Batteries in parallel do not add to the voltage of the circuit

Circuit Diagrams: More About Series Circuits Capacitors in Series: Recall: V 1 + V 2 + V 3 = V total for series circuit Capacitors in series act like one big capacitor C 2 = 0.8 F 1.5 V C 1 = 1.2 F C 3 = 0.4 F

Circuit Diagrams: More About Series Circuits C total = ??? 1.5 V Equivalent Circuit

Circuit Diagrams: More About Series Circuits C total = 0.2 F 1.5 V Equivalent Circuit

Circuit Diagrams: More About Parallel Circuits 1.5 V C 1 = 1.2 F C 2 = 0.8 F C 3 = 0.4 F

Circuit Diagrams: More About Parallel Circuits 1.5 V C total = 2.4 F Equivalent Circuit

Circuits in Both Series and Parallel Many circuits utilize both series and parallel circuit properties within a circuit Case in point: How do you find the equivalent resistance of this circuit? Recommend: drawing equivalent circuits

Equivalent Circuits Strategy: equivalent circuits Pick out parts that are exclusively in series or in parallel Simplify that part of circuit Repeat as needed until only one equivalent circuit component remains Question: What part should be simplified first for this problem?

Equivalent Circuits

Step 2: Series Circuit R 1 + R eqv + R 5 = R total 1.0 Ω Ω Ω = R total 5.0 Ω = R total

Equivalent Circuits Step 2: Series Circuit R 1 + R eqv + R 5 = R total 1.0 Ω Ω Ω = R total 5.0 Ω = R total

Equivalent Circuits Try this one on your own! Step 1 Step 2 Step 3

As You Come In… How should a voltmeter be inserted into a circuit? How should an ammeter be inserted into a circuit? V Parallel: V equal for both branches Very high R so very little current comes through

As You Come In… How should a voltmeter be inserted into a circuit? How should an ammeter be inserted into a circuit? V Parallel: V equal for both branches Very high R so very little current comes through A Series: I equal since along same path Very small R so very little voltage lost to device