# Power efficiency of Battery with Internal Ressitance

Watch
Announcements
#1
Hi, I have a question i want to ask that i got in the physics AS examination. I will draw a diagram of the circuit.
0
#2
Not sure if I have the right values. The question was something like that : what is the power efficiency of the battery. How would you do it ?
0
#3
anyone ?
0
2 months ago
#4
(Original post by papie)
anyone ?
I mean, you can calculate the ratio of if you had another component in the circuit... but with just an internal resistance I can't see how you'd be able to get an "efficiency" per-say from this... someone else might know more?

Edit: Didn't see that XY was actually a component- there's nothing there to indicate it on the diagram (you should draw in a resistor between X and Y- I thought that thing on the top right was just "X1" or something else unrelated to the problem. In the textbook I got afforded for circuits they usually use a "dummy resistor" to represent wire resistance as opposed to drawing two nodes and slapping a label to them.

The power is just given by and since it's a series, this will reduce to

Solve for internal resistance and you'll have your problem solved. Note that is fractional and not a percentage.
Last edited by Callicious; 2 months ago
0
2 months ago
#5
Find the total resistance by doing R = V/I. Then find the useful power and total power using the total resistance and the load resistance (the resistance between x and y). Finally, find efficiency using efficiency = useful power/total power
0
#6
(Original post by Callicious)
I mean, you can calculate the ratio of if you had another component in the circuit... but with just an internal resistance I can't see how you'd be able to get an "efficiency" per-say from this... someone else might know more?

Edit: Didn't see that XY was actually a component- there's nothing there to indicate it on the diagram (you should draw in a resistor between X and Y- I thought that thing on the top right was just "X1" or something else unrelated to the problem. In the textbook I got afforded for circuits they usually use a "dummy resistor" to represent wire resistance as opposed to drawing two nodes and slapping a label to them.

The power is just given by and since it's a series, this will reduce to

Solve for internal resistance and you'll have your problem solved. Note that is fractional and not a percentage.
It's very different than what i did . It is probably wrong but i will write down what i did: I first calculated the Internal resistance then did P=VI to find max power of battery w/o internal resistance using the same value for current(probably sure value of current is different w/o internal resistance). Then i did P=I^2r to find the power loss in the internal resistance. To get %efficiency i did (Power loss in internal Resistance/ VI ). That was a 3 mark question BTW in AS physics CIE exam this year. Also the question was something like this: What is the efficiency of the battery in delivering power to resistance XY(It wasn't phrased like this but something like that ) .
0
X

new posts
Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### What is your favourite revision method?

Taking notes manually (41)
23.56%
Note taking apps (5)
2.87%
Flashcards (31)
17.82%
Revision guides (5)
2.87%
Past papers (86)
49.43%
Something else (let us know in the thread) (6)
3.45%