- #1
JoakimvE
- 8
- 0
I am currently doing a lab trying to calculate internal resitance of a battery. Do I use the formula V=IR?
Internal Resistance of a Battery
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Homework Help Overview
The discussion revolves around calculating the internal resistance of a battery in a lab setting, with participants exploring the relevant formulas and experimental setups.
Discussion Character
- Exploratory, Conceptual clarification, Problem interpretation
Approaches and Questions Raised
- Participants discuss using the formula V=IR and question the role of circuit resistance. There are mentions of using variable resistors and measuring current and voltage to derive internal resistance. Some express confusion about the effects of measurement tools like ammeters and voltmeters on results, and whether internal resistance is constant.
Discussion Status
The conversation includes various attempts to clarify the experimental approach and the relationship between voltage, current, and resistance. Some participants provide insights into the effects of measurement devices, while others express uncertainty about their experimental values and the variability of resistance.
Contextual Notes
Participants note the importance of accurately measuring voltage and current, and there is mention of needing to account for the effects of different types of meters used in the experiment. Additionally, there is a concern about how to quantify the resistance added during the experiment.
- #2
ramollari
- 433
- 1
What do you denote by R? The circuit connected to the battery also has resistance?
[tex]Emf = I(R_{batt} + R_{circ})[/tex]
[tex]Emf = I(R_{batt} + R_{circ})[/tex]
- #3
Quarkycharm
- 15
- 0
Using a variable resistor, take different values of R and find the values of the current (I) and voltage (V). Draw a graph of V against I, find the slope as it'll give you -r (which is the internal resistance of the battery) .
- #4
JoakimvE
- 8
- 0
you mean to say, that an ammeter or voltmeter would come to effect my results? 
- #5
JoakimvE
- 8
- 0
and that Internal Resistance is relative to the electric current.
- #6
Nylex
- 552
- 2
JoakimvE said:you mean to say, that an ammeter or voltmeter would come to effect my results?
What do you mean?
. Surely you know that if you increase resistance, current will decrease and voltage will increase?- #7
JoakimvE
- 8
- 0
yes... ofcourse i know that... but i mean, is Internal Resistance of a Battery a constant or not?
- #8
Nylex
- 552
- 2
Yes, it is constant.
- #9
JoakimvE
- 8
- 0
okay...
damn, my values are confusing the hell out of me...
damn, my values are confusing the hell out of me...
- #10
Quarkycharm
- 15
- 0
JoakimvE,
Hey it's simple. What are the steps of the experiment you're conducting to find internal R? Are you using a variable resistor or only adding resistors to the circuit?
Hey it's simple. What are the steps of the experiment you're conducting to find internal R? Are you using a variable resistor or only adding resistors to the circuit?
- #11
Integral
Staff Emeritus
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This depends on the meters you are using. If you are using a modern digital meter, then then I doubt that you will be able to detect their presence. If you are using an old fashioned analog meter with a D'Arsonal/needle movement, then yes, they will have a measurable effect.JoakimvE said:you mean to say, that an ammeter or voltmeter would come to effect my results?
An ammeter is an addional resistance in series and a voltmeter is a resistance in parallel to the measured resistance.
- #12
JoakimvE
- 8
- 0
variable resistor
- #13
JoakimvE
- 8
- 0
okay, thanks a lot. I am understanding this way more now (even though I am not much of an electrician :zzz:).
anyhow, i guess the main problem is how much i varied the resistance by. i just varied the electric field (E)... I am guessing i can't calculate the resistance i added.
anyhow, i guess the main problem is how much i varied the resistance by. i just varied the electric field (E)... I am guessing i can't calculate the resistance i added.
- #14
Quarkycharm
- 15
- 0
Emf = V(terminals) + V(lost)
You actually don't need to.. First, short circuit the battery to find its emf. Set up your circuit with the variable resistor, voltmeter and ammeter connected properly. Now increase the resistance by moving the slide and record 5 reading for voltage and current (from the voltmeter and ammeter)
Plot a graph of V against I and calculate the slope as it would represent -r The straight line you've drawn is represented by this equation:
V = (-r)I + E
E: battery emf
-rI: voltage lost due to internal resistance
V: voltage across terminals, measured by voltmeter
Hope that cleared things out for you, if you need me to explain it more let me know, I'd be glad to help.
JoakimvE said:
You actually don't need to.. First, short circuit the battery to find its emf. Set up your circuit with the variable resistor, voltmeter and ammeter connected properly. Now increase the resistance by moving the slide and record 5 reading for voltage and current (from the voltmeter and ammeter)
Plot a graph of V against I and calculate the slope as it would represent -r The straight line you've drawn is represented by this equation:
V = (-r)I + E
E: battery emf
-rI: voltage lost due to internal resistance
V: voltage across terminals, measured by voltmeter
Hope that cleared things out for you, if you need me to explain it more let me know, I'd be glad to help.
- #15
JoakimvE
- 8
- 0
no i got it. thanks a lot.