text stringlengths 2 2.33k | source stringclasses 826
values |
|---|---|
Drift velocityvdvdis the average speed at which these charges move. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
CurrentIIis proportional to drift velocityvdvd, as expressed in the relationshipI=nqAvdI=nqAvd. Here,IIis the current through a wire of cross-sectional areaAA. The wireâs material has a free-charge densitynn, and each carrier has chargeqqand a drift velocityvdvd. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Electrical signals travel at speeds about10121012times greater than the drift velocity of free electrons. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
A simple circuitisone in which there is a single voltage source and a single resistance. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
One statement of Ohmâs law gives the relationship between currentII,
voltageVV,
and resistanceRRin a simple circuit to beI=VR.I=VR. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Resistance has units of ohms (ΩΩ), related to volts and amperes by1 Ω=1 V/A1 Ω=1 V/A. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
There is a voltage orIRIRdrop across a resistor, caused by the current flowing through it, given byV=IRV=IR. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
The resistanceRRof a cylinder of lengthLLand cross-sectional areaAAisR=ÏLAR=ÏLA, whereÏÏis the resistivity of the material. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Values ofÏÏinTable 20.1show that materials fall into three groupsâconductors, semiconductors, and insulators. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Temperature affects resistivity; for relatively small temperature changesÎTÎT, resistivity isÏ=Ï0(1+αÎT)Ï=Ï0(1+αÎT), whereÏ0Ï0is the original resistivity andααis the temperature coefficient of resistivity. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Table 20.2gives values forαα, the temperature coefficient of resistivity. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
The resistanceRRof an object also varies with temperature:R=R0(1+αÎT)R=R0(1+αÎT), whereR0R0is the original resistance, andRRis the resistance after the temperature change. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Electric powerPPis the rate (in watts) that energy is supplied by a source or dissipated by a device. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Three expressions for electrical power areP=IV,P=IV,P=V2R,P=V2R,andP=I2R.P=I2R. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
and | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
The energy used by a device with a powerPPover a timettisE=PtE=Pt. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Direct current (DC) is the flow of electric current in only one direction. It refers to systems where the source voltage is constant. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
The voltage source of an alternating current (AC) system puts outV=V0sin 2ÏftV=V0sin 2Ïft, whereVVis the voltage at timett,V0V0is the peak voltage, andffis the frequency in hertz. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
In a simple circuit,I=V/RI=V/Rand AC current isI=I0sin 2ÏftI=I0sin 2Ïft, whereIIis the current at timett, andI0=V0/RI0=V0/Ris the peak current. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
The average AC power isPave=12I0V0Pave=12I0V0. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Average (rms) currentIrmsIrmsand average (rms) voltageVrmsVrmsareIrms=I02Irms=I02andVrms=V02Vrms=V02, where rms stands for root mean square. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Thus,Pave=IrmsVrmsPave=IrmsVrms. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Ohmâs law for AC isIrms=VrmsRIrms=VrmsR. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Expressions for the average power of an AC circuit arePave=IrmsVrmsPave=IrmsVrms,Pave=Vrms2RPave=Vrms2R, andPave=Irms2RPave=Irms2R, analogous to the expressions for DC circuits. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
The two types of electric hazards are thermal (excessive power) and shock (current through a person). | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Shock severity is determined by current, path, duration, and AC frequency. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Table 20.3lists shock hazards as a function of current. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Figure 20.22graphs the threshold current for two hazards as a function of frequency. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Electric potentials in neurons and other cells are created by ionic concentration differences across semipermeable membranes. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Stimuli change the permeability and create action potentials that propagate along neurons. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
Myelin sheaths speed this process and reduce the needed energy input. | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
This process in the heart can be measured with an electrocardiogram (ECG). | https://openstax.org/books/college-physics-2e/pages/20-section-summary |
ammeter : an instrument that measures current | https://openstax.org/books/college-physics-2e/pages/21-glossary |
analog meter : a measuring instrument that gives a readout in the form of a needle movement over a marked gauge | https://openstax.org/books/college-physics-2e/pages/21-glossary |
bridge device : a device that forms a bridge between two branches of a circuit; some bridge devices are used to make null measurements in circuits | https://openstax.org/books/college-physics-2e/pages/21-glossary |
capacitance : the maximum amount of electric potential energy that can be stored (or separated) for a given electric potential | https://openstax.org/books/college-physics-2e/pages/21-glossary |
capacitor : an electrical component used to store energy by separating electric charge on two opposing plates | https://openstax.org/books/college-physics-2e/pages/21-glossary |
conservation laws : require that energy and charge be conserved in a system | https://openstax.org/books/college-physics-2e/pages/21-glossary |
current : the flow of charge through an electric circuit past a given point of measurement | https://openstax.org/books/college-physics-2e/pages/21-glossary |
current sensitivity : the maximum current that a galvanometer can read | https://openstax.org/books/college-physics-2e/pages/21-glossary |
digital meter : a measuring instrument that gives a readout in a digital form | https://openstax.org/books/college-physics-2e/pages/21-glossary |
electromotive force (emf) : the potential difference of a source of electricity when no current is flowing; measured in volts | https://openstax.org/books/college-physics-2e/pages/21-glossary |
full-scale deflection : the maximum deflection of a galvanometer needle, also known as current sensitivity; a galvanometer with a full-scale deflection of50 μA50 μAhas a maximum deflection of its needle when50 μA50 μAflows through it | https://openstax.org/books/college-physics-2e/pages/21-glossary |
galvanometer : an analog measuring device, denoted by G, that measures current flow using a needle deflection caused by a magnetic field force acting upon a current-carrying wire | https://openstax.org/books/college-physics-2e/pages/21-glossary |
internal resistance : the amount of resistance within the voltage source | https://openstax.org/books/college-physics-2e/pages/21-glossary |
Jouleâs law : the relationship between potential electrical power, voltage, and resistance in an electrical circuit, given by:Pe=IVPe=IV | https://openstax.org/books/college-physics-2e/pages/21-glossary |
junction rule : Kirchhoffâs first rule, which applies the conservation of charge to a junction; current is the flow of charge; thus, whatever charge flows into the junction must flow out; the rule can be statedI1=I2+I3I1=I2+I3 | https://openstax.org/books/college-physics-2e/pages/21-glossary |
Kirchhoffâs rules : a set of two rules, based on conservation of charge and energy, governing current and changes in potential in an electric circuit | https://openstax.org/books/college-physics-2e/pages/21-glossary |
loop rule : Kirchhoffâs second rule, which states that in a closed loop, whatever energy is supplied by emf must be transferred into other forms by devices in the loop, since there are no other ways in which energy can be transferred into or out of the circuit. Thus, the emf equals the sum of theIRIR(voltage) drops i... | https://openstax.org/books/college-physics-2e/pages/21-glossary |
null measurements : methods of measuring current and voltage more accurately by balancing the circuit so that no current flows through the measurement device | https://openstax.org/books/college-physics-2e/pages/21-glossary |
Ohmâs law : the relationship between current, voltage, and resistance within an electrical circuit:V=IRV=IR | https://openstax.org/books/college-physics-2e/pages/21-glossary |
ohmmeter : an instrument that applies a voltage to a resistance, measures the current, calculates the resistance using Ohmâs law, and provides a readout of this calculated resistance | https://openstax.org/books/college-physics-2e/pages/21-glossary |
parallel : the wiring of resistors or other components in an electrical circuit such that each component receives an equal voltage from the power source; often pictured in a ladder-shaped diagram, with each component on a rung of the ladder | https://openstax.org/books/college-physics-2e/pages/21-glossary |
potential difference : the difference in electric potential between two points in an electric circuit, measured in volts | https://openstax.org/books/college-physics-2e/pages/21-glossary |
potentiometer : a null measurement device for measuring potentials (voltages) | https://openstax.org/books/college-physics-2e/pages/21-glossary |
RC circuit : a circuit that contains both a resistor and a capacitor | https://openstax.org/books/college-physics-2e/pages/21-glossary |
resistance : causing a loss of electrical power in a circuit | https://openstax.org/books/college-physics-2e/pages/21-glossary |
resistor : a component that provides resistance to the current flowing through an electrical circuit | https://openstax.org/books/college-physics-2e/pages/21-glossary |
series : a sequence of resistors or other components wired into a circuit one after the other | https://openstax.org/books/college-physics-2e/pages/21-glossary |
shunt resistance : a small resistanceRRplaced in parallel with a galvanometer G to produce an ammeter; the larger the current to be measured, the smallerRRmust be; most of the current flowing through the meter is shunted throughRRto protect the galvanometer | https://openstax.org/books/college-physics-2e/pages/21-glossary |
terminal voltage : the voltage measured across the terminals of a source of potential difference | https://openstax.org/books/college-physics-2e/pages/21-glossary |
voltage : the electrical potential energy per unit charge; electric pressure created by a power source, such as a battery | https://openstax.org/books/college-physics-2e/pages/21-glossary |
voltage drop : the loss of electrical power as a current travels through a resistor, wire or other component | https://openstax.org/books/college-physics-2e/pages/21-glossary |
voltmeter : an instrument that measures voltage | https://openstax.org/books/college-physics-2e/pages/21-glossary |
Wheatstone bridge : a null measurement device for calculating resistance by balancing potential drops in a circuit | https://openstax.org/books/college-physics-2e/pages/21-glossary |
The total resistance of an electrical circuit with resistors wired in a series is the sum of the individual resistances:Rs=R1+R2+R3+....Rs=R1+R2+R3+.... | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Each resistor in a series circuit has the same amount of current flowing through it. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
The voltage drop, or power dissipation, across each individual resistor in a series is different, and their combined total adds up to the power source input. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
The total resistance of an electrical circuit with resistors wired in parallel is less than the lowest resistance of any of the components and can be determined using the formula:1Rp=1R1+1R2+1R3+....1Rp=1R1+1R2+1R3+.... | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Each resistor in a parallel circuit has the same full voltage of the source applied to it. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
The current flowing through each resistor in a parallel circuit is different, depending on the resistance. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
If a more complex connection of resistors is a combination of series and parallel, it can be reduced to a single equivalent resistance by identifying its various parts as series or parallel, reducing each to its equivalent, and continuing until a single resistance is eventually reached. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
All voltage sources have two fundamental partsâa source of electrical energy that has a characteristic electromotive force (emf), and an internal resistancerr. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
The emf is the potential difference of a source when no current is flowing. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
The numerical value of the emf depends on the source of potential difference. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
The internal resistancerrof a voltage source affects the output voltage when a current flows. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
The voltage output of a device is called its terminal voltageVVand is given byV=emfâIrV=emfâIr, whereIIis the electric current and is positive when flowing away from the positive terminal of the voltage source. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
When multiple voltage sources are in series, their internal resistances add and their emfs add algebraically. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Solar cells can be wired in series or parallel to provide increased voltage or current, respectively. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Kirchhoffâs rules can be used to analyze any circuit, simple or complex. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Kirchhoffâs first ruleâthe junction rule: The sum of all currents entering a junction must equal the sum of all currents leaving the junction. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Kirchhoffâs second ruleâthe loop rule: The algebraic sum of changes in potential around any closed circuit path (loop) must be zero. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
The two rules are based, respectively, on the laws of conservation of charge and energy. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
When calculating potential and current using Kirchhoffâs rules, a set of conventions must be followed for determining the correct signs of various terms. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
The simpler series and parallel rules are special cases of Kirchhoffâs rules. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Voltmeters measure voltage, and ammeters measure current. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
A voltmeter is placed in parallel with the voltage source to receive full voltage and must have a large resistance to limit its effect on the circuit. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
An ammeter is placed in series to get the full current flowing through a branch and must have a small resistance to limit its effect on the circuit. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Both can be based on the combination of a resistor and a galvanometer, a device that gives an analog reading of current. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Standard voltmeters and ammeters alter the circuit being measured and are thus limited in accuracy. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Null measurement techniques achieve greater accuracy by balancing a circuit so that no current flows through the measuring device. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
One such device, for determining voltage, is a potentiometer. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Another null measurement device, for determining resistance, is the Wheatstone bridge. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Other physical quantities can also be measured with null measurement techniques. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
AnRCRCcircuit is one that has both a resistor and a capacitor. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
The time constantÏÏfor anRCRCcircuit isÏ=RCÏ=RC. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
When an initially uncharged (V0=0V0=0att=0t=0) capacitor in series with a resistor is charged by a DC voltage source, the voltage rises, asymptotically approaching the emf of the voltage source; as a function of time,V=emf(1âeât/RC)(charging).V=emf(1âeât/RC)(charging). | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Within the span of each time constantÏÏ, the voltage rises by 0.632 of the remaining value, approaching the final voltage asymptotically. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
If a capacitor with an initial voltageV0V0is discharged through a resistor starting att=0t=0, then its voltage decreases exponentially as given byV=V0eât/RC(discharging).V=V0eât/RC(discharging). | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
In each time constantÏÏ, the voltage falls by 0.368 of its remaining initial value, approaching zero asymptotically. | https://openstax.org/books/college-physics-2e/pages/21-section-summary |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.