What is Internal resistance: Definition and 157 Discussions

A practical electrical power source which is a linear electric circuit may, according to Thévenin's theorem, be represented as an ideal voltage source in series with an impedance. This impedance is termed the internal resistance of the source. When the power source delivers current, the measured voltage output is lower than the no-load voltage; the difference is the voltage drop (the product of current and resistance) caused by the internal resistance. The concept of internal resistance applies to all kinds of electrical sources and is useful for analyzing many types of electrical circuits.

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  1. O

    Internal Resistance of a Real Battery

    Homework Statement A solar cell generates a potential difference of 0.10 V when a 400 ohm resistor is connected across it, and a potential difference of 0.15 V when a 900 ohm resistor is substituted. What is the internal resistance of the solar cell? Homework Equations E - ir - iR = 0...
  2. O

    Internal Resistance of a Real Battery + Resistance of the Circuit

    Homework Statement (a) In the figure shown, show that the rate at which energy is dissipated in R as thermal energy is a maximum when R = r. (b) Show that this maximum power is P = EMF2/4r. http://www.practicalphysics.org/imageLibrary/jpeg400/208.jpg The only difference between this...
  3. A

    Kirchoff's laws, emf and internal resistance

    Homework Statement two identical cells of emf E and internal resistance r are connected in series. a 7 ohm resistor is connected across the combination and draws a current of 0.333A. the two cells are now connected in parallel; the 7 ohm resistor now draws a current of 0.375A from the...
  4. V

    Accumulator Battery Internal Resistance & Charger Potential: A Doubt

    This is in continuation to https://www.physicsforums.com/showthread.php?t=330495 The question that initiated my doubt reads this -- " the internal resistance of an accumulator battery of emf 6V is 10 Ohm when fully discharged . as battery gets charged up , its internal resistance drops to 1...
  5. L

    Calculating Internal Resistance and Maximizing Power Transfer in a 24V Supply

    Homework Statement A 24 voltt supply has a terminal voltage of 20 volts when connected to a 40R Load Resistor. Calculate the internal resistance of the supply State the conditions under which maximum power will be transferred to load. Homework Equations V = E - Ir V = p.d...
  6. R

    Internal Resistance in battery

    Homework Statement A resistor has a resistance R, and a battery has an internal resistance r. When the resistor is connected across the battery, ten percent less power is dissipated in R than there would be if the battery had no internal resistance. Find the ratio r/R Homework Equations...
  7. V

    Internal Resistance Graph

    When taking internal resistance into account, voltage/current graph has negative gradient (i.e. internal resistance).? My thoughts... Because for ohmic resistors, graph has a positive gradient. Why does one say that when V=0, Current = max, whilst the other says that when V=0, Current = 0?
  8. G

    Calculating EMF and Current in a Circuit with Internal Resistance

    Homework Statement A 5.60ohm resistor is connected to a battery that has 0.200ohm internal resistance, and a terminal voltage of the battery is 10.0V. What is the current in the resistor? What is the emf of the battery? Homework Equations EMF=terminal voltage+(I)(Rint.) V=RI The...
  9. L

    As Internal resistance and emf question

    If a cell is connected with an external resistor of 6V and a switch and a voltmeter is connected across the terminals of the cell which reads 2.6 V when the switch is open and 2.4 V when the switch is closed, how do you find the emf and the internal resistance? so far i tried doing: V = IR...
  10. L

    Electricity Experiment (Internal Resistance)

    1. Hi I'm going to a physics Summer camp but they asked me to carry out my own experiment. This is because my dad's a physics teacher and he has a lot of equipment readily available to him. I have to find the internal resistance of a dc power supply with the following equipment given: Power...
  11. J

    Electric Circuit and Internal Resistance Lab

    Homework Statement I performed a lab where we designed an electric circuit on paper and then calculated the Current, Power, and Voltage for each of the resistors. We used one power supply. Then we built the circuit we designed and then measured the actual Current Power and Voltage for the it...
  12. C

    How to model internal resistance

    If I set up a coil with thin wire, push a magnet through it, and connect either end to a voltmeter (in series), then is this an accurate way to measure the total voltage? I might not be phrasing this right, so ask me to clarify if I should. I'm guessing that you can't just simplify a circuit...
  13. B

    Calculating Power Dissipated by a Battery

    Hey I am very new here (litrally signed up 10 mins ago after trying to search the net for this problem) heres what it looks like in my c/w so far I've worked out the total resistance of the open circuit but the next question is asking i attempted to use ohms law but that would of been...
  14. S

    Emf and internal resistance of a battery

    When switch S in the figure is open, the voltmeter V of the battery reads 3.07 V. When the switch is closed, the voltmeter reading drops to 2.95 V, and the ammeter A reads 1.70 A. Assume that the two meters are ideal, so they do not affect the circuit. Find the value of the emf. (see picture...
  15. S

    EMF and Internal Resistance (2)

    Homework Statement A battery consisting of six cells in series, each of e.m.f 1.5V and internal resistance 0.5 Ohms is connected to two 3 Ohm resistors which are in parallel. Calculate: a) the total parallel resistance of the combination [1.67] b) write down the internal resistance of the...
  16. S

    EMF and Internal Resistance (1)

    Homework Statement A torch bulb is marked 2.5V and 0.3A. When it is connected to a dry battery of e.m.f 3.0V the correct p.d of 2.5V is produced across it. Calculate the internal resistance if the battery.Homework Equations I=V/R?The Attempt at a Solution It's on paper - sorry!Answer = 1.67 -...
  17. O

    Internal resistance of a digital multimeter

    Homework Statement Provided that the input resistance of the DMM is much larger than the resistance values in the circuit to which it is connected, the DMM will not draw a significant current. Estimate the input resistance of the DMM by connecting the 10 M resistor supplied in series with...
  18. G

    Internal Resistance: Solving for Battery Emf 9.30 V and Load 60.0 Ω

    Homework Statement A battery having an emf of 9.30 V delivers 103 mA when connected to a 60.0 ohms load. Determine the internal resistance of the battery. Homework Equations V = E - IR The Attempt at a Solution i plugged in 9.3 for V, .103 for I, and 60, for R... and i got...
  19. DaTario

    Internal resistance of a batery

    Hi All, I would like to know what is the precise meaning of the internal resistance of a DC source of voltage. Does it have some chemical contribution (as for instance, mean time for the reaction to occur, mean velocity of difusion of charge through the acid solution, or something like...
  20. N

    Calculate Internal Resistance: I, R, V & More

    How can I go about calculating internal resistance? I have variables I, R, and V but no idea on how to find the 'internal' resistance. Is this some sort of special case?
  21. J

    Internal resistance of an ammeter

    Homework Statement Devise a NON DESTRUCTIVE scheme to measure the resistance of the 0-1mA meter that is provided in the lab. You may make use of an external power supply (or battery) and other circuit components such as resistors to make your measurement. Design your measurement scheme so that...
  22. S

    Internal resistance of battery

    Homework Statement a battery with unknown internal resistance and open circuit potential (emf) is connected toa 3 ohm external resistor. the terminal potential is found to be 60 volts. when the same battery is connected to a 48 ohm resistor, the terminal potential is 96 volts. what is the...
  23. N

    Electric Car Battery Internal Resistance Effects

    The battery of an electric car consists of 30 cells, connected in series, to supply current to the motor. (a) Assume that the internal resistance of each cell is negligible and that the pd across each cell is 6.0V. (i) State the pd across the motor. (ii) The battery provides 7.2kW to the...
  24. L

    What is the value of the loss volt and internal resistance of the battery?

    Homework Statement When a current of 2A flows the p.d across a battery's terminal falls from 12V to 9V. (a) What is the value of the loss volt? (b) What is the internal resistance of the battery? Homework Equations Lost Volt = Ir The Attempt at a Solution (a) 12V - 9V = 3V R =...
  25. C

    Internal resistance of a solar cell; strange results?

    Homework Statement Basically, my task is to find out the internal resistance of a solar cell. I set-up a circuit as seen here (http : / / mt14 . quickshareit . com / share / picture666d18 . png), and measured the Current and Voltage on different settings of resistance in 5Ohm intervals from...
  26. I

    Internal resistance of a source

    Homework Statement A rule of thumb used to determine the internal resistance of a source is that it is the open-circuit voltage divided by the short-circuit current. Is this correct? Why or why not? thx for any help
  27. N

    Solve Internal Resistance Homework Problem

    Homework Statement "A 6.0V battery is connected across a parallel combination of two resistors ; one 10 ohm and one 40 ohm. Thee total current provided by the battery is 0.25A. Obtain a value for the internal resistance. Homework Equations E= IR +Ir The Attempt at a Solution...
  28. M

    How is internal resistance of a cell related to temperature

    Relevant equations int rest =emf - terminal potential / current or r=E-V/I The attempt at a solution Since Emf of a cell is inversely proportional to temp (From Nernst Equation of Emf of a cell), from the above equation, if temp is high, E is low, therefore r is low. So, acc. to me...
  29. D

    Finding out internal resistance of a lemon when used as a power supply

    Hi There, Right I recently did an experiment in Physics to find out the internal resistance of a lemon when used as a power supply. We connected the lemon to a voltmeter, ammeter and variable resistor, changed the resistance on the variable resistance and measured the voltage and current...
  30. D

    Finding the emf and internal resistance of a cell

    I hope someone can help me with my coursework by making sure my method is ok and is actually correct for my experiment. Note. I will not actually be doing this it is just a plan of what I could do! 1. I am provided with a cell of approcimate EMF 1.5V, an approximate internal resistance of 1Ω...
  31. I

    Electric Circuit Help (Emf and Internal Resistance)

    1. Find the current in, and the potential difference across, each resistor in the circuit shown below: The circuit is a simple parallel circuit with 2.0 ohms at the first resistor, 10.0 ohms at the second, and 20.0 ohms at the third The problem also gives you Emf which is 12.0 V and the...
  32. A

    EMF and internal resistance

    Homework Statement Hi, my first post here. :smile: Anyway I am struggling with this homework, can someone help me out, show me what to do please. 1)a cell can supply a current of 1.2A through two 2ohm resistors connected in parallel. When they are connected in series the value of the...
  33. R

    What is the internal resistance r of the battery?

    Homework Statement The potential difference across the terminals of a battery is 8.20 V when there is a current of 1.54 A in the battery from the negative to the positive terminal. When the current is 3.56 A in the reverse direction, the potential difference becomes 9.40 V. What is the...
  34. A

    Exploring E.m.f and Internal Resistance: A Graphical Approach

    Homework Statement This problem relates to an experiment to determine the e.m.f and internal resistance of a battery using a variable load. Taking values for V & I a graphy of V vs. I was plotted. Homework Equations E=IR+Ir V=IR The Attempt at a Solution After plotting the graph...
  35. D

    How Do You Calculate Internal Resistance and Current Flow in a Circuit?

    Homework Statement Hi I've tried to solve this question but I keep getting stuck at a certain point, it probably very simple but any tips would be greatly appreciated The EMF of a cell is measured using a potentiometer and is found to be 1.51V. When a voltmeter, which has a resistance of...
  36. S

    Internal resistance circuit problem

    Homework Statement In a circuit, two identical batteries with EMF of 22 V and internal resistance of 7 Ohm are placed in parallel to provide power to a load resistance of RL = 35 Ohms. What is the power transferred from the current to RL to heat the resistor? Homework Equations Is R(L)...
  37. M

    Why does the internal resistance of a cell increase as it ages?

    I want to understand that why does the internal resistance of a cell/battery goes on increasing as the cell gets older. What happens inside the cell that causes the internal resistance to increase gradually? Thanks.
  38. K

    Internal resistance ratio problem

    1. The problem: A resistor has a resistance R, and a battery has an internal resistance r. When the resistor is connected across the battery, ten percent less power is dissipated in R than would be dissipated if the battery had no internal resistance. Find the ratio r/R. 2. Homework...
  39. P

    Find Inner Resistance of Power Source: 5 Trials

    If I do 5 trials of measuring voltage and current of a circuit (with different resistors for each trial), how would I find the inner resistance of the power source?
  40. S

    What is the internal resistance of a battery?

    Does a battery really have any internal resistance? If it has then what's the origin of the resistance. We know that the electrons flow from negative to positive terminal of a battery. Do the electrons just end up releasing energy(such as heat) at the terminal/ or combines with the atoms of the...
  41. E

    Working out internal resistance.

    I have two different circuits and I need to work out the internal resistance of the cell. So far I have got to 0.8(5+r)=1.2(2.5+r) Where do I go from here?
  42. N

    Internal Resistance of Solar cell

    Hi, I am trying to do coursework on measuring the internal resistance of a solar cell. The light intensity on the solar cell is not going to change so the only thing that can be changed is the resistance as a variable resistor is used.But I am not sure how to find the internal resistance when I...
  43. O

    Please help Circuit analysis (Thevenin voltage and internal resistance)

    URGENT! Please help! Circuit analysis (Thevenin voltage and internal resistance) Hi guys, I am really stuck on this portion of my lab and it's due tomorrow! Please help! I have two questions: The first deals with the diagram from the left of the attached picture. I have to prove that...
  44. F

    How Do You Calculate EMF and Internal Resistance in a Circuit?

    Here is the question I need to solve: A battery has an emf E and an internal resistance r. When the battery is connected to a 25 ohm resistor, the current through the battery is 0.75 A. When the battery is connected to a 53 ohm resistor, the current is 0.45 A. Find the emf of battery and...
  45. M

    Can the Slope of a Graph Determine EMF and Internal Resistance?

    I'm doing a few practicals at home this summer, and the one that is bugging me is about EMF. I have measured voltage and current at different resistances across a 4,5 V battery, and made a graph. But to find the emf, am I supposed to take the slope of the graph, or the gradient? Or is that the...
  46. T

    Emf + Internal Resistance of Battery

    These circuit questions seem to give me so many problems, this question in particular. What are the emf and internal resistance of the battery in the figure below? I have the answers, that emf is 9V and internal resistance is 0.5 ohms, however I'm having problems getting there. What...
  47. H

    Find R: Internal Resistance Equation

    In this equation I r= E-V/V*R How would I find R? thanks in advance you your help.
  48. K

    Why does internal resistance occur?

    I know its because the electrons stop the current but that's about all i Know! Any ideas also does internal resistance vary from rechargable and non rechargable batteries? thanks :D
  49. N

    Physics Q&A: Internal Resistance in Series with Variable Resistor

    Hi, I am in yr 11 and i study physics I am my free time but have stumnbled across the following question that i can't seem to find an answer for in any books, would someone please be able to help me? A cell is connected in series with a variable resistor. A high resistance voltmeter is...
  50. N

    Internal resistance and electromotive force problem

    help me with this please... i just couldn't get it. 1) a complete circuit consists of a 12.0 V battery with a 4.50 ohm resistor and switch. the internal resistance of the battery is 0.30 ohms when switch is open. what does the voltmeter read when placed: a. across the terminal of the...
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