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Finding amount of charges

  • Thread starter Kyoma
  • Start date
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1. Homework Statement
The e.m.f of a battery is 12V and provides an electrical energy of 500J. What is the amount of charges flowing in the battery for 5 seconds?

2. The attempt at a solution

Since V=W/Q, rearranging the equation gives you Q=W/V:

Q= 500/12 = 41.6666667 C

But, I don't know what is the 5 seconds for. So, I just put 41.6666667 C as the answer and I got it wrong.
 

tiny-tim

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My 'W' is work done and 'Q' is amount of charge?
 

tiny-tim

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Yeah. :(
 
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Kyoma,did you post the actual question or did you change the wording?
 
2,442
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Hello tiny-tim. I'm assuming that the energy is provided in a time period of 5 seconds but the question as presented above does not make that clear.
 
97
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I posted the actual question.

My answer is correct. My professor marked it wrong.
 
2,442
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Kyomo,a 12V battery transfers 12J of energy to every coulomb of charge that passes through it so 500 J would be transferred to a charge of 500/12=41.7C.This is the answer you got but the question asks for something different, it asks how much charge flows in 5 seconds.
The question does not make sense and needs clarifying.
 
785
15
1. Homework Statement
The e.m.f of a battery is 12V and provides an electrical energy of 500J. What is the amount of charges flowing in the battery for 5 seconds?

2. The attempt at a solution

Since V=W/Q, rearranging the equation gives you Q=W/V:

Q= 500/12 = 41.6666667 C

But, I don't know what is the 5 seconds for. So, I just put 41.6666667 C as the answer and I got it wrong.
Hi Kyoma! :smile:


nooo :redface:, V = W/I

(watts = volts times amps :wink:)​
I posted the actual question.

My answer is correct. My professor marked it wrong.


You are correct , Kyoma .
But Tiny Tim is also not wrong .
He conceptually refers to the work done by a unit charge in t seconds .

http://www.csgnetwork.com/ohmslaw2.html"


V=12 V
W=500 J
T= 5 s

So

W = VxI
500 = 12 x Q/t ( since I=Q/t)
500 = 12 x q/5
2500 = 12Q
Q=208.33 C

Is this the answer ? Your professor hasn't marked it wrong .:wink:

_____________________________________________________________________




W work done on Q charge in T sec .
So On 1 unit of charge work done will be w/q

so it will do more work in t sec so final formula will be :

V=WT/Q

:wink:


Hey By sheer logic , Kyoma what you do is you multiply your answer by 5 , ie
41.6666667x5 = 208.5 (approximately).


^_^
 
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