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Why are the chemicals able to produce a unique potential difference? Quantum mechanical descriptions of molecules, which take into account the types of atoms and numbers of electrons in them, are able to predict the energy states they can have and the energies of reactions between them.

In the case of a lead-acid battery, an energy of 2 eV is given to each electron sent to the anode. Voltage is defined as the electrical potential energy divided by charge: V = P E q size 12{V= { {P rSub { size 8{E} } } over {q} } } {} . An electron volt is the energy given to a single electron by a voltage of 1 V. So the voltage here is 2 V, since 2 eV is given to each electron. It is the energy produced in each molecular reaction that produces the voltage. A different reaction produces a different energy and, hence, a different voltage.

Terminal voltage

The voltage output of a device is measured across its terminals and, thus, is called its terminal voltage     V size 12{V} {} . Terminal voltage is given by

V = emf Ir , size 12{V="emf" - ital "Ir"} {}

where r size 12{r} {} is the internal resistance and I size 12{I} {} is the current flowing at the time of the measurement.

I size 12{I} {} is positive if current flows away from the positive terminal, as shown in [link] . You can see that the larger the current, the smaller the terminal voltage. And it is likewise true that the larger the internal resistance, the smaller the terminal voltage.

Suppose a load resistance R load size 12{R rSub { size 8{"load"} } } {} is connected to a voltage source, as in [link] . Since the resistances are in series, the total resistance in the circuit is R load + r size 12{R rSub { size 8{"load"} } +r} {} . Thus the current is given by Ohm’s law to be

I = emf R load + r . size 12{I= { {"emf"} over {R rSub { size 8{"load"} } +r} } } {}
This schematic drawing of an electrical circuit shows an e m f, labeled as script E, driving a current through a resistive load R sub load and through the internal resistance r of the voltage source. The current is shown flowing in a clockwise direction from the positive end of the source.
Schematic of a voltage source and its load R load size 12{R rSub { size 8{"load"} } } {} . Since the internal resistance r size 12{r} {} is in series with the load, it can significantly affect the terminal voltage and current delivered to the load. (Note that the script E stands for emf.)

We see from this expression that the smaller the internal resistance r size 12{r} {} , the greater the current the voltage source supplies to its load R load size 12{R rSub { size 8{"load"} } } {} . As batteries are depleted, r size 12{r} {} increases. If r size 12{r} {} becomes a significant fraction of the load resistance, then the current is significantly reduced, as the following example illustrates.

Calculating terminal voltage, power dissipation, current, and resistance: terminal voltage and load

A certain battery has a 12.0-V emf and an internal resistance of 0 . 100 Ω size 12{0 "." "100" %OMEGA } {} . (a) Calculate its terminal voltage when connected to a 10.0- Ω size 12{"10" "." 0- %OMEGA } {} load. (b) What is the terminal voltage when connected to a 0 . 500- Ω size 12{0 "." "500-" %OMEGA } {} load? (c) What power does the 0 . 500- Ω size 12{0 "." "500-" %OMEGA } {} load dissipate? (d) If the internal resistance grows to 0 . 500 Ω size 12{0 "." "500 " %OMEGA } {} , find the current, terminal voltage, and power dissipated by a 0 . 500- Ω size 12{0 "." "500-" %OMEGA } {} load.

Strategy

The analysis above gave an expression for current when internal resistance is taken into account. Once the current is found, the terminal voltage can be calculated using the equation V = emf Ir size 12{V="emf" - ital "Ir"} {} . Once current is found, the power dissipated by a resistor can also be found.

Solution for (a)

Entering the given values for the emf, load resistance, and internal resistance into the expression above yields

I = emf R load + r = 12 . 0 V 10 . 1 Ω = 1 . 188 A . size 12{I= { {"emf"} over {R rSub { size 8{"load"} } +r} } = { {"12" "." 0" V"} over {"10" "." "1 " %OMEGA } } =1 "." "188"" A"} {}

Enter the known values into the equation V = emf Ir size 12{V="emf" - ital "Ir"} {} to get the terminal voltage:

Questions & Answers

Describe an experiment to determine short half life
Tyson Reply
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Kenedy Reply
A 20MH coil has a resistance of 50 ohms and us connected in series with a capacitor to a 520MV supply
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Sujitha
Physics is the branch of science that deals with the study of matter and the interactions it undergoes with energy
Junior
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A 20MH coil has a resistance of 50 ohms and is connected in series with a capacitor to a 250MV supply if the circuit is to resonate at 100KHZ, Determine 1: the capacitance of the capacitor 2: the working voltage of the circuit, given that pie =3.142
Musa
Heat is transfered by thermal contact but if it is transfered by conduction or radiation, is it possible to reach in thermal equilibrium?
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Yes, It is possible by conduction if Surface is Adiabatic
Astronomy
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Kalilu
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Kalilu
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Moses
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Noman
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Ekwunazor Reply
your fat arse sitting all day is a good reference of three dimensional numbnut
Universe
Noman
Yes the Universe itself
Astronomy
Examine different types of shoes, including sports shoes and thongs. In terms of physics, why are the bottom surfaces designed as they are? What differences will dry and wet conditions make for these surfaces?
Lathan Reply
sports shoes are designed in such a way they are gripped well with your feet and their bases have and high friction surfaces, Thong shoes are for comfort, these are easily removed and light weight. these are usually low friction surfaces but in wet conditions they offer greater friction.
Noman
thong sleepers are usually used in restrooms.
Noman
what is wave
Ochigbo Reply
The phenomenon of transfer of energy
Noman
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Lord Reply
you mean in three dimensions......numbnut
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Lord
if it flows in three dimensions does it mean if an object theoretically moves beyond the speed of light it won't experience time
Lord
time seems to flow in one direction...but I the past present and future happen every moment time flies regardless.
but if an object moves beyond the speed of light time stops right for it
Lord
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Lord
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Noman
if v=ktx Ly Mz find the value of x,y and z
Emmanuel Reply
x=v=ktx Ly Mz find the value of x,y and z
y=v=ktx Ly Mz find the value of x,y and z
z=v=ktx Ly Mz find the value of x,y and z
now get your lazy arse up and clean the kitchen 😁
I want to join the conversation
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😂
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Stephen
what conversation you talking about? .....numbnut
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Bridget Reply
T=2π√(m÷k).K is spring constance
Ambe
T=2π√m/k
Lord
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Lebatam Reply
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Matthew
Practice Key Terms 4

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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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