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21.2 Electromotive force: terminal voltage  (Page 5/13)

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Some batteries can be recharged by passing a current through them in the direction opposite to the current they supply to a resistance. This is done routinely in cars and batteries for small electrical appliances and electronic devices, and is represented pictorially in [link] . The voltage output of the battery charger must be greater than the emf of the battery to reverse current through it. This will cause the terminal voltage of the battery to be greater than the emf, since V = emf − Ir size 12{V="emf" - ital "Ir"} {} , and I size 12{I} {} is now negative.

The diagram shows a car battery being charged with cables from a battery charger. The current flows from the positive terminal of the charger to the positive terminal of the battery, through the battery and back out the negative terminal of the battery to the negative terminal of the charger.
A car battery charger reverses the normal direction of current through a battery, reversing its chemical reaction and replenishing its chemical potential.

Multiple voltage sources

There are two voltage sources when a battery charger is used. Voltage sources connected in series are relatively simple. When voltage sources are in series, their internal resistances add and their emfs add algebraically. (See [link] .) Series connections of voltage sources are common—for example, in flashlights, toys, and other appliances. Usually, the cells are in series in order to produce a larger total emf.

But if the cells oppose one another, such as when one is put into an appliance backward, the total emf is less, since it is the algebraic sum of the individual emfs.

A battery is a multiple connection of voltaic cells, as shown in [link] . The disadvantage of series connections of cells is that their internal resistances add. One of the authors once owned a 1957 MGA that had two 6-V batteries in series, rather than a single 12-V battery. This arrangement produced a large internal resistance that caused him many problems in starting the engine.

This diagram shows two typical batteries in series, with the positive terminal of the first touching the negative terminal of the second. The schematic diagram of the electric current flowing through them is shown as current I passing through the series of two cells of e m f script E sub one and internal resistance r sub one and e m f script E sub two and internal resistance r sub two.
A series connection of two voltage sources. The emfs (each labeled with a script E) and internal resistances add, giving a total emf of emf 1 + emf 2 size 12{"emf" rSub { size 8{1} } +"emf" rSub { size 8{2} } } {} and a total internal resistance of r 1 + r 2 size 12{r rSub { size 8{1} } +r rSub { size 8{2} } } {} .
The left side of the diagram shows a battery that contains a combination of a large number of cells. The right side shows a set of cells combined in series to form a battery.
Batteries are multiple connections of individual cells, as shown in this modern rendition of an old print. Single cells, such as AA or C cells, are commonly called batteries, although this is technically incorrect.

If the series connection of two voltage sources is made into a complete circuit with the emfs in opposition, then a current of magnitude I = emf 1 – emf 2 r 1 + r 2 size 12{I= { { left ("emf" rSub { size 8{1} } - "emf" rSub { size 8{2} } right )} over {r rSub { size 8{1} } +r rSub { size 8{2} } } } } {} flows. See [link] , for example, which shows a circuit exactly analogous to the battery charger discussed above. If two voltage sources in series with emfs in the same sense are connected to a load R load size 12{R rSub { size 8{"load"} } } {} , as in [link] , then I = emf 1 + emf 2 r 1 + r 2 + R load size 12{I= { { left ("emf" rSub { size 8{1} } - "emf" rSub { size 8{2} } right )} over {r rSub { size 8{1} } +r rSub { size 8{2} } +R rSub { size 8{"load"} } } } } {} flows.

The diagram shows a closed circuit containing series connection of two cells of e m f script E sub one and internal resistance r sub one and e m f script E sub two and internal resistance r sub two. The positive end of E sub one is connected to the positive end of E sub two.
These two voltage sources are connected in series with their emfs in opposition. Current flows in the direction of the greater emf and is limited to I = emf 1 − emf 2 r 1 + r 2 size 12{I= { { left ("emf" rSub { size 8{1} } - "emf" rSub { size 8{2} } right )} over {r rSub { size 8{1} } +r rSub { size 8{2} } } } } {} by the sum of the internal resistances. (Note that each emf is represented by script E in the figure.) A battery charger connected to a battery is an example of such a connection. The charger must have a larger emf than the battery to reverse current through it.
Part a shows a flashlight glowing when connected to two cells joined in series with the positive end of one cell connected to the negative end of the other. Part b shows the schematic circuit for part a. There is a series combination of two cells of e m f script E sub one and internal resistance r sub one and e m f script E sub two and internal resistance r sub two connected to a load resistor R sub load.
This schematic represents a flashlight with two cells (voltage sources) and a single bulb (load resistance) in series. The current that flows is I = emf 1 + emf 2 r 1 + r 2 + R load size 12{I= { { left ("emf" rSub { size 8{1} } - "emf" rSub { size 8{2} } right )} over {r rSub { size 8{1} } +r rSub { size 8{2} } +R rSub { size 8{"load"} } } } } {} . (Note that each emf is represented by script E in the figure.)

Questions & Answers

Three charges q_{1}=+3\mu C, q_{2}=+6\mu C and q_{3}=+8\mu C are located at (2,0)m (0,0)m and (0,3) coordinates respectively. Find the magnitude and direction acted upon q_{2} by the two other charges.Draw the correct graphical illustration of the problem above showing the direction of all forces.
Kate Reply
To solve this problem, we need to first find the net force acting on charge q_{2}. The magnitude of the force exerted by q_{1} on q_{2} is given by F=\frac{kq_{1}q_{2}}{r^{2}} where k is the Coulomb constant, q_{1} and q_{2} are the charges of the particles, and r is the distance between them.
Muhammed
What is the direction and net electric force on q_{1}= 5µC located at (0,4)r due to charges q_{2}=7mu located at (0,0)m and q_{3}=3\mu C located at (4,0)m?
Kate Reply
what is the change in momentum of a body?
Eunice Reply
what is a capacitor?
Raymond Reply
Capacitor is a separation of opposite charges using an insulator of very small dimension between them. Capacitor is used for allowing an AC (alternating current) to pass while a DC (direct current) is blocked.
Gautam
A motor travelling at 72km/m on sighting a stop sign applying the breaks such that under constant deaccelerate in the meters of 50 metres what is the magnitude of the accelerate
Maria Reply
please solve
Sharon
8m/s²
Aishat
What is Thermodynamics
Muordit
velocity can be 72 km/h in question. 72 km/h=20 m/s, v^2=2.a.x , 20^2=2.a.50, a=4 m/s^2.
Mehmet
A boat travels due east at a speed of 40meter per seconds across a river flowing due south at 30meter per seconds. what is the resultant speed of the boat
Saheed Reply
50 m/s due south east
Someone
which has a higher temperature, 1cup of boiling water or 1teapot of boiling water which can transfer more heat 1cup of boiling water or 1 teapot of boiling water explain your . answer
Ramon Reply
I believe temperature being an intensive property does not change for any amount of boiling water whereas heat being an extensive property changes with amount/size of the system.
Someone
Scratch that
Someone
temperature for any amount of water to boil at ntp is 100⁰C (it is a state function and and intensive property) and it depends both will give same amount of heat because the surface available for heat transfer is greater in case of the kettle as well as the heat stored in it but if you talk.....
Someone
about the amount of heat stored in the system then in that case since the mass of water in the kettle is greater so more energy is required to raise the temperature b/c more molecules of water are present in the kettle
Someone
definitely of physics
Haryormhidey Reply
how many start and codon
Esrael Reply
what is field
Felix Reply
physics, biology and chemistry this is my Field
ALIYU
field is a region of space under the influence of some physical properties
Collete
what is ogarnic chemistry
WISDOM Reply
determine the slope giving that 3y+ 2x-14=0
WISDOM
Another formula for Acceleration
Belty Reply
a=v/t. a=f/m a
IHUMA
innocent
Adah
pratica A on solution of hydro chloric acid,B is a solution containing 0.5000 mole ofsodium chlorid per dm³,put A in the burret and titrate 20.00 or 25.00cm³ portion of B using melting orange as the indicator. record the deside of your burret tabulate the burret reading and calculate the average volume of acid used?
Nassze Reply
how do lnternal energy measures
Esrael
Two bodies attract each other electrically. Do they both have to be charged? Answer the same question if the bodies repel one another.
JALLAH Reply
No. According to Isac Newtons law. this two bodies maybe you and the wall beside you. Attracting depends on the mass och each body and distance between them.
Dlovan
Are you really asking if two bodies have to be charged to be influenced by Coulombs Law?
Robert
like charges repel while unlike charges atttact
Raymond
What is specific heat capacity
Destiny Reply
Specific heat capacity is a measure of the amount of energy required to raise the temperature of a substance by one degree Celsius (or Kelvin). It is measured in Joules per kilogram per degree Celsius (J/kg°C).
AI-Robot
specific heat capacity is the amount of energy needed to raise the temperature of a substance by one degree Celsius or kelvin
ROKEEB
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Source:  OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
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