Emf in a circuit (multiple choice question)

[EF17xx]

Homework Statement

Correct answer is

Homework Equations

emf = I(R + r)

The Attempt at a Solution

When current flows the voltage across the battery is less than the emf so it's not A
I really don't understand why the answer is C because B, C, D all seem correct to me.
Please help me with this question

 

[Orodruin]

How do you compute the thermal energy dissipated in the battery? How do you compute the chemical energy transformed in the battery? How do you compute the energy dissipated in the resistor?

 

[EF17xx]

How do you compute the thermal energy dissipated in the battery? How do you compute the chemical energy transformed in the battery? How do you compute the energy dissipated in the resistor?

I'm not sure because my textbook does not explain this.

 

[Orodruin]

I'm not sure because my textbook does not explain this.

I do not believe that. It is a basic thing that is explained in virtually every textbook on electric circuits.

What is the power dissipated in a resistor?

 

[EF17xx]

I know that chemical energy established the current and is transformed into thermal energy as current heats wire.

P= I^2R
P= VI
P = V^2/R

So what is the difference between power dissipated and chemical energy and thermal energy in battery and resistor?

 

[Orodruin]

The chemical energy transformed is the amount of chemical energy from the battery that is discharged. The power dissipated as thermal energy is the amount of electric energy that is dissipated as heat from the battery. Those are not the same things, if the internal resistance of the battery would be zero no heat would be dissipated from it.

 

[Orodruin]

P= VI

So use this one. What is the relation between dissipated power and total dissipated energy?

 

[EF17xx]

Are they the same?

Sorry, I'm confused,

The correct answer is answer C, it might help if you could explain why.

 

[Orodruin]

Are they the same?

No, power and energy are not the same things and are not measured in the same units.

The correct answer is answer C, it might help if you could explain why.

Yes, I know that, but giving away answers is not how PF works. You will learn a lot more if you get to do the thought process yourself with some guidance.

 

[EF17xx]

ok
Power is Energy per time
Energy is measured in Joules and 1 Joule is work done to move 1 kg 1 m.
Voltage is work done to move a charge. V=W/q

So is it answer C because not all of the chemical energy is transformed into thermal?
Therefore it can't be 6 Joules but chemical energy is 6 Joules?

 

[Orodruin]

So is it answer C because not all of the chemical energy is transformed into thermal?

No. All of the energy is dissipated as thermal energy. You have moved 1 C across a voltage of 6 V and so clearly the energy conversion is 6 J.

The question is where the thermal energy is dissipated. For example, how much energy is dissipated through the resistor?