Electrical circuits confirmation

[yesgirl10]

Homework Statement

Hi, I just need some confirmation on this question on whether it is correct or not.

Homework Equations

P= V^2/R.
Based on that circuit I was asked to complete the following table and then find the power of the circuit.

The Attempt at a Solution

To find power I did the total voltage squared, divided by the total resistance. However, I was having second thoughts on the total resistance. Is it just all of them added together? Because I was taught that it was just the voltage divided by the current.

P=3^2/10. P=9/10. P=0.9W. Is this correct?

 

[yesgirl10]

pictures

Here are the pictures.

 

[NascentOxygen]

You have to add all of the individual I².R terms (or E²/R or V.I products). You cannot simply sum all the resistor values!

There is a check you can do, to confirm you have the right answer. Can you see it?

 

[yesgirl10]

Oh okay, so everything is alright then? And I am not sure about the check. I know that P=V^2/R as well as P=V(I). So to find the power for the whole circuit I used the total values and both equations gave me the same answer.

 

[NascentOxygen]

Oh okay, so everything is alright then? And I am not sure about the check. I know that P=V^2/R as well as P=V(I). So to find the power for the whole circuit I used the total values and both equations gave me the same answer.

That will exactly equal the power drawn from the battery, 3.0x0.3 W (EDIT)

You were not given the value of R3, but had to work it out?

 

[yesgirl10]

That will exactly equal the power drawn from the battery, 30x0.3 W

You were not given the value of R3, but had to work it out?

I'm really confused, sorry. Where did the 30 come from? And I worked it out by doing 0.48V/0.06A. Did I do that part wrong?

 

[NascentOxygen]

I'm really confused, sorry. Where did the 30 come from? And I worked it out by doing 0.48V/0.06A. Did I do that part wrong?

Oh, the decimal point went missing. That should be 3.0x 0.3 Watts. That's the power delivered by the battery. It equals the power dissipated by all the resistors.

0.48V/0.06A is correct for R3.

 

[yesgirl10]

Oh, the decimal point went missing. That should be 3.0x 0.3 Watts. That's the power delivered by the battery. It equals the power dissipated by all the resistors.

0.48V/0.06A is correct for R3.

Okay, thank you!