Circuits and Circuit Elements Electricity Circuits and Circuit Elements

Circuits Electric circuit – a set of electrical components connected so that they provide one or more complete paths for the movement of charges Charges move from the battery through a path back to the battery

Circuits Switches are used to open and close the circuit If the circuit is open, there is no complete path for the charge to travel If the circuit is closed, there is at least one complete path for the charge to travel Charge cannot flow, so there is no current

Circuits Schematic diagram – a graphic representation of an electric circuit or apparatus, with standardized symbols for the circuit components

Circuits

Series and Parallel Circuits Series – describes a circuit or portion of a circuit that provides a single conducting path One path for current to travel If one element is removed, the circuit will not work If one element doesn’t work, the circuit will not work

Series and Parallel Circuits Parallel – describes components in a circuit that are connected across common points, providing two or more separate conducting paths More than one pathway Charge moves through the path of least resistance If one part is removed or doesn’t work the circuit may continue to work

Electric Power and Electrical Energy Electrical energy – the energy associated with electrical charges, whether moving or at rest Electric power – the rate at which electrical energy is used in a circuit The rate at which electrical work is done Power = Current * Potential Difference P=IV Power = (Current)2 * Resistance P=I2R Power = (Potential Difference)2 / Resistance P= V2 / R Measured in Watts (W) Electric companies measure energy consumed in kilowatt-hours (kWh) The greater the power produced by a given current or potential difference, the smaller the resistance

Fuses and Circuit Breakers Overloaded – condition when electrical wires carry more than a safe level of current Short circuit – accidental creation of an alternative pathway Reduces the resistance in the circuit Increases the current

Fuses and Circuit Breakers Short circuits Leads to overload Grounding is used to prevent electric shock from short circuits Fuse – an electrical device containing a metal strip that melts when current in the circuit becomes to great Used to prevent overload

Fuses and Circuit Breakers Circuit breaker – a device that protects a circuit from current overloads Trip when the current overloads Acts like a switch

Resistors in Series Series – describes a circuit or portion of a circuit that provides a single conducting path without junctions When resistors are arranged in series, the current flowing through each resistor is the same Equivalent resistance – the total resistance of a circuit

Resistors in Series

Resistors in Series For resistors in series, the equivalent resistance is equal to the sum of all of the resistors Req = R1 + R2 + R3… Total Potential difference (voltage) = Current * Equivalent Resistance VTot = IReq The equivalent resistance of a series combination of resistors is always greater than any individual resistance

Resistors in Series Potential difference across a given resistor can be calculated by multpying the current (which is constant) by the resistance of the given resistor V1 = IR1 or V2 = IR2 In a series circuit, all of the elements must be able to conduct electrical charge If one bulb goes out or one wire gets disconnected, the entire circuit fails

Resistors in Parallel Parallel – describes two or more components in a circuit that are connected across common points or junctions, providing separate conducting pats for the current There is more than one pathway through the circuit or part of a circuit Resistors in parallel have the same potential difference across them V is constant The sum of the individual currents in parallel resistors equals the total current ITot = I1 + I2 + I3 …

Resistors in Parallel

Resistors in Parallel The equivalent resistance of resistors in parallel can be calculated using a reciprocal relationship 1/Req = 1/R1 + 1/R2 + 1/R3 … The equivalent resistance is always less than the smallest resistance in the group of resistors Parallel circuits do not require all elements to conduct The circuit will continue so long as there is at least one complete pathway from one terminal to the other

Resistors in Parallel

Resistors Combined Both in Parallel and in Series Complex circuits have resistors arranged both in series and in parallel You must simplify the groups of resistors Work with a small group that is all in series or in parallel After you have simplified the small groups, start combining groups until you have “created” a de facto simple circuit Work backward to find current or potential difference

Resistors Combined Both in Parallel and in Series

Resistors Combined Both in Parallel and in Series