- #1

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## Homework Statement

Can somebody explain what ems is for a person (me) who has only heard of voltage?

http://imgur.com/Y1JQy7w

Lets say the batteries volt is 10V. Is it always gonna be 10? Is the batteries ems 10V?

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- Thread starter Drizzy
- Start date

- #1

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Can somebody explain what ems is for a person (me) who has only heard of voltage?

http://imgur.com/Y1JQy7w

Lets say the batteries volt is 10V. Is it always gonna be 10? Is the batteries ems 10V?

- #2

gneill

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An

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- #4

gneill

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I am not familiar with the term "ems". Can you provide a definition or a source for where you found it?

A good approximate model for a real battery is an ideal cell with a particular emf (otherwise known as its voltage) in series with a small resistance that represents the battery's internal resistance -- the non-ideal manifestation of the real chemistry and materials that make up the battery. The analysis and design of practical circuits might involve this resistance.

This internal resistance may come into play when you need to determine how the voltage that appears at a battery's terminals changes with the electrical load on the battery (current drawn), or how much power is lost inside the battery (causing it to heat up!) for a given load. It also plays a role in charging a (rechargeable) battery, since it can limit the charging current for a given charger voltage.

- #5

gneill

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It is in swedish :P I am wondering if the ems is used in P=UI and when do I need the ems value?

- #7

gneill

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Ah! Swedish. That would explain it then. So I then interpret ems to be the same as emf in English.It is in swedish :P I am wondering if the ems is used in P=UI and when do I need the ems value?

In your circuit, if the battery is said to have an ems of 10 Volts, and since no internal resistance is given for that battery then that ems of 10 V will be impressed across the load resistor R (5 Ohms). This results in a current ##I = ems/R = 10/5 = 2 A## to flow, as shown in your figure.

- #8

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so the voltage is 8 then?

- #9

gneill

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You would have to calculate the new current given the new total resistance; Adding resistance to the circuit will decrease the current.

so the voltage is 8 then?

- #10

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the total resistance is 6 ohms

the voltage is 10 V

The current is 10/6

U = 10 - (1*10/6) = 10 - 10/6 = (60/6) - (10/6) = 50/6 = 8.3333333....

is this correct?

- #11

gneill

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Yes. You could also have found the potential drop across R using the current flowing through it: V = (10/6 A)(5 Ω)

the total resistance is 6 ohms

the voltage is 10 V

The current is 10/6

U = 10 - (1*10/6) = 10 - 10/6 = (60/6) - (10/6) = 50/6 = 8.3333333....

is this correct?

- #12

ehild

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I wondered where "s" came from. Is it that?Ah! Swedish. That would explain it then. So I then interpret ems to be the same as emf in English.

https://sv.wikipedia.org/wiki/Elektromotorisk_spänning

- #13

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Yes and we also write U=RI not V=RI

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