Current and Circuits

Current current: the flow of charged particles. E Current is measured in Amperes (A) which is made of the unit of a Coulomb/sec (C/s). How much current passes through a wire as 6.0 C flows in 1.5 s? 4.0 A = 4.0 x 6.25 x electrons/sec = 2.5 x electrons/sec An Ampere is defined as a fundamental unit of electricity.

Drift velocity: the resulting velocity due to the application of an electric field and the random motions and collisions by charges. Direct Current (DC) – current that travels in only one direction -batteries supply current and voltage that are direct Alternating Current (AC) – current that travels in two directions -home, business, school outlets, AC generators Types of Current:

Current Conventions E positive charge motion E negative charge motion conventional current - the flow of positive charges (protons). -Positive charges flow from high to low potential electric current - the flow of negative charges (electrons). Negative charges flow from low to high potential.

circuit: A continuous path for charges to flow through. Circuits Circuit simulation

Circuit Components V V + - Power source: A device that can produce and maintain a potential difference. The source of the electric field that can exert a force on the charges in the circuit. The power source is measured in volts. Multi-cell batterySingle cell battery Voltage Source Generator Types of power sources: ~ AC EMF (electromotive force): An open terminal battery. (A battery not part of a circuit.) Schematic: A diagram that uses symbols to represent circuit components. Multiple voltage of a single cell 3.0 V + - DC 50 V

Resistor: A circuit device that is designed specifically to limit current flow. Resistance is a restriction to current flow. Any device can be modeled with a resistor. The larger the resistor/resistance the smaller the current that flows through them. Resistor/Resistance is measured in Ohms (Ω). Ω – Greek capital letter Omega Voltage (Potential Difference) is lost through resistors. Wire: The medium through which charges flow.

Circuit Components Continued Circuit Breaker: A device designed to interrupt current flow in the circuit if the current exceeds a certain level. Circuit breakers can be reset and reused after being activated. Fuse: A device designed to interrupt current flow in a circuit if the current exceeds a certain level. Fuses must be replaced after they blow. Switch: A device used to start and stop the flow of current in a circuit.

Power Source Configurations Power sources can placed in various configurations to achieve increased current or voltage. 1.0 V 2.0 V 3.0 V V Power sources In this configuration (series) Increase voltage 1.0 V V Power sources in this configuration (parallel) Increase current.

Battery Configurations Cells within a 9.0 V battery Battery Configurations

Series/Parallel Paths Series Path Parallel Paths ---

Series/Parallel Paths Series: a region in a circuit in with only one current path Parallel: a region in a circuit with multiple current paths Series Parallel

Circuit Measuring Devices A Ammeter: A device that measures current in an electrical circuit. -ammeters have an extremely low internal resistance -ammeters are placed in series with circuit components Voltmeter: A device that measures voltage (potential difference) in an electrical circuit. - voltmeters have an extremely high internal resistance -voltmeters are placed in parallel with circuit components V Circuit measuring devices have minimal influence on the circuit.

Ammeter Placement A Device I I I I II or A Device The ammeter is in series because there is only one path for the current An ammeter will read positive if conventional current enters the positive ammeter terminal. + +

Voltmeter Placement I Device V I A voltmeter will read positive if conventional current enters the positive voltmeter terminal. IVIV IVIV The voltmeter is in parallel with the device because there are alternate paths between the device and voltmeter for the current IDID IDID +

Simple Circuit

Simple Circuit Schematic A V I + _ + - V V R R Ohms Law: V=IR V = voltage (V) I = current (A) R = resistance (Ω) R is constant for a circuit that obeys Ohm’s Law. Power and Energy in a Circuit: P=VI P=I 2 R P=V 2 /R E=Pt Power is measured in Watts. Energy is measured in Joules. I V + - (specific to resistors) t = time (s)

Simple Circuit Animation

Series Circuits

Series Resistor Circuits Resistors are in series when there is only one current path between the individual resistors. The current in each resistor is the same. + _ V I V1 V2 V3 The sum of the voltages in a closed loop must equal zero. V-V1-V2-V3 = 0 or V=V1+V2+V3 V=IR1+IR2+IR3 V=I(R1+R2+R3) V=I(Req) R1 R2 R Req=equivalent resistance The equivalent resistance (Req) is the single resistor that has the same effect in the circuit as the resistors it replaces. Req=R1+R2+R3+…

Equivalent Circuit V + - I Req + - V I=V/R eq

Series Circuit Animation

Series Resistor Concepts The more resistors in series, the smaller the circuit current. The larger the resistance, the greater the amount of voltage lost across the resistor. The resistor with the largest value uses the most voltage and power for series resistors. Each resistor in series has an overall influence on the total circuit current.

Parallel Resistor Circuits Resistors are in parallel when there are multiple current paths. Voltages across each resistor in parallel are the same. V + - I R1 I1I2 I3 R2 R3 I2+I3 I=I 1 +I 2 +I 3 The equivalent resistance for resistors in parallel is always smaller than the smallest resistor. More resistors in parallel decreases the equivalent resistance of the circuit. Home/Business circuits are wired in parallel. I2+I3 I1+I2+I3

Equivalent Circuit V + - I Req + - V I=V/R eq

Parallel Animation

Parallel Resistor Concepts The voltage of each parallel resistor is the same as the source voltage. The equivalent resistance for resistors in parallel is always smaller than the smallest resistor. More resistors in parallel decreases the equivalent resistance of the circuit. The current in each branch is affected only by the resistance of each branch. The resistor with the smallest value uses the most power for parallel resistors. The more resistors in parallel, the larger the total circuit current.

Home/Business Wiring Circuit breaker outlets Inside view of outlet wiring Transmission lines from outside Alternating Current ~ Neutral/ground line