What Is the EMF of a Cell with Given Energy Dissipation and Current?

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Homework Help Overview

The problem involves a cell connected in series with a resistor, where energy dissipation and current are provided. The objective is to determine the electromotive force (emf) of the cell based on the given energy losses in both the cell and the resistor.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the calculation of power based on energy and time, questioning the original poster's approach to finding power. There are attempts to clarify the relationship between energy, power, and voltage in the context of the emf equation.

Discussion Status

Some participants have provided guidance on how to calculate power correctly and suggested using the series current to find voltage drops. There is an ongoing exploration of the calculations related to the emf, but no explicit consensus has been reached regarding the final answer.

Contextual Notes

Participants are working with specific values for energy dissipation and current, but there may be confusion regarding the application of formulas and the interpretation of results. The original poster expresses uncertainty about progressing further in the problem.

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Homework Statement


A cell is connected in series with a resistor and supplies a current of 4.0 A for a time of 500 s. During this time, 1.5 kJ of energy is dissipated in the cell and 2.5 kJ of energy is dissipated in the resistor.

What is the emf of the cell?

A. 0.50 V

B. 0.75 V

C. 1.5 V

D. 2.0 V

cheers

Homework Equations


V=IR
P=IV=I^2R
P= energy/time
Emf= V+Ir

The Attempt at a Solution


Power dissipated in the cell is 1500 x 500 = 750000 W
Voltage of the cell= 750000/4 = 187500 V
Power dissipated in the resistor is 2500 x 500 = 1250000 W
Voltage of the cell= 1250000/4= 312500 V

However, I do not know how to refer those to the emf equation.
Emf= IR+Ir = 4(R+r)

I cannot go further than this

Could you guys please solve this question for me...?

Thanks
 
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SUSUSUSUSUSUSUSU said:
Power dissipated in the cell is 1500 x 500 = 750000 W
Power is Energy divided by time, not multiplied by it. Does that help?

Basically use the Energy and time to find the power in Ri and Rl, then use the series current to figure out the voltage drop across each. Add those to get the total EMF of the battery...
 
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berkeman said:
Power is Energy divided by time, not multiplied by it. Does that help?

Basically use the Energy and time to find the power in Ri and Rl, then use the series current to figure out the voltage drop across each. Add those to get the total EMF of the battery...
Thank you, you are right!

I got 3W for the cell and 5W for the resistor!

3=4xV.
Therfore V=3/4
5=4xV
Therefore V=5/4

Emf= IR+Ir = 3/4 + 5/4 =2

Is that it??
 
SUSUSUSUSUSUSUSU said:
Emf= IR+Ir = 3/4 + 5/4 =2

Is that it??
That's what I got as well. Good work! :smile:
 
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berkeman said:
That's what I got as well. Good work! :smile:
Thanks a loooot!
 
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