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Transcript
CIRCUITS AND RESISTANCE RECALL: Current Potential Difference The flow of electrons Causes electrons to flow Symbol I V Units Amps (A) Volts (V) Definition Formula (if applicable) How measured (if applicable) I=Q t Ammeter V=E Q Voltmeter Circuits: A circuit is made up of a power supply, connecting wires & various elements that allow electrons to leave a power source, travel through the elements & return back to the power source. Common Electric Symbols Battery/Power Source Bulb Common symbols (cont’d) Switch Push-button Switch Resistor Voltmeter Ammeter V A Circuits Power Supply A v Ammeter Resistor Voltmeter Trick to help identify type of circuit: Series:Pen follows wire Types of Circuits: Parallel: Pen can go in more than one direction There are 2 types of circuits: 1. 2. SERIES Series Circuit Parallel Circuit PARALLEL Series or Parallel? 1. 2. PARALLEL SERIES 3. 4. A PARALLEL SERIES A Resistance Symbol: R Units:Ohms, Ω Resistance is how difficult it is for current to flow • A device with HIGH Resistance will have very little current passing through it • A device with low resistance will have a large current passing through it A resistor is used to slow current down IF: R is High than I is low R is Low than I is high Equivalent Resistance - Req Equivalent Resistance is the TOTAL resistance of a circuit Symbol: Req Units: Ohms = Ω Formulae: Series: Req = R1 + R2 + R3 + … Parallel: 1 1 1 1 ... Re q R1 R 2 R3 What is the equivalent (Req) of the circuit below? 5W 3W 10 W Type of circuit: Series Formula: Req = R1 + R2 + R3 Req = 10 + 5 + 3 Req = 18 W resistance What is the equivalent (Req) of the circuit below? 75 W 30 W Type of circuit: Series Formula: Req = R1 + R2 Req = 75 +30 Req = 105 W resistance What is the equivalent resistance (Req) of the circuit below? 10 Ω 15 Ω Type of circuit: Parallel Formula: 1 ÷ 0.1666 = 6Ω 1 1 1 Re q R1 R2 1 1 1 Re q 10 15 1 0.1 0.0666 Re q 1 0.1666 Re q Re q 6W What is the equivalent resistance (Req) of the circuit below? 15 W 5W 15 W Type of circuit: Parallel Formula: 1 ÷ 0.3333 = 3Ω 1 1 1 1 Re q R1 R2 R3 1 1 1 1 Re q 15 5 15 1 0.0666 0.2 0.0666 Re q 1 0.3333 Re q Re q 3W KEY POINTS Symbols of circuit parts: Voltmeter, Ammeter, Power Supply, Resistor Two types of circuits (series and parallel) Formula for Req (equivalent resistance) Series – Req = R1 + R2 + R3 1 1 1 1 Parallel Req R 1 R2 R3 RECALL: Resistance Current Potential Difference Definition Slows current down The flow of electrons Causes electrons to flow Symbol R I V Units Ohms (Ω) Amps (A) Volts (V) Formula (if applicable) R=V I How measured (if applicable) Calculated I=Q t Ammeter V=E Q Voltmeter