Finding amount of charges

Kyoma

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.

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tiny-tim

Homework Helper
Hi Kyoma! Since V=W/Q …
nooo , V = W/I

(watts = volts times amps )​

Kyoma

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

tiny-tim

Homework Helper
My 'W' is work done and 'Q' is amount of charge?
ohh!
… provides an electrical energy of 500J.
are you sure the question says that?

the question would normally give the power of a battery, not the (total stored?) energy Kyoma

Yeah. :(

Kyoma,did you post the actual question or did you change the wording?

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.

Kyoma

I posted the actual question.

My answer is correct. My professor marked it wrong.

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.

sankalpmittal

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! nooo , V = W/I

(watts = volts times amps )​
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 . _____________________________________________________________________

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 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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