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. B

    Finding internal resistance from 2 circuits

    Homework Statement A battery with an emf of 60 V and an internal resistance (r) is connected to a 10 ohm external resistance. The power lost inside the battery is 50w. The same battery is then connected to a 4.0 ohm resistance. The power loss is 200w. What is the internal resistance of the...
  2. P

    Electric circuit problem, finding internal resistance

    1. A battery whose emf is 6.0 V is connected to a 2.0 Ω resistor. The voltage drop across the 2.0 Ω resistor is 5.0 V. What is its internal resistance? a) 0.40 Ω b) 1.7 Ω c) 2.4 Ω d) 2.5 Ω Homework Equations VT=ε-Ir The Attempt at a Solution I know that ε=6.0 V VT=5.0 V...
  3. J

    Calculate the emf of Battery w/ External & Internal Resistance

    Homework Statement What is the emf of the battery shown? there is an external resistance of 2.50 ohm and 4.0 A...The battery has an internal resistance of 0.50ohm Homework Equations V=Ir V= E +/- IR The Attempt at a Solution Since the current is going away the battery then i...
  4. B

    Two Batteries In Series-Total EMF and Internal Resistance

    Two Batteries In Series--Total EMF and Internal Resistance Homework Statement Two 1.50-V batteries—with their positive terminals in the same direction—are inserted in series into the barrel of a flashlight. One battery has an internal resistance of 0.260 Ω, the other an internal resistance of...
  5. W

    Internal resistance understanding

    Hello, I'm having difficulty trying to understand internal resistance of any component. I don't understand how exactly the internal resistance affects the current and what exactly is the terminal pd? And for calculating resistance, voltage, pd, emf, current and all those basic things -...
  6. R

    Question on internal resistance.

    I recently encountered circuits with the source having internal resistance, and it became confusing applying Kirchoff's Rules. What I did is this: assuming the loop is counter clockwise: -------wire - negative terminal +positive terminal (conventional flow) when...
  7. P

    Working out EMF and internal resistance

    Homework Statement Power supply of EMF = E and internal resistance of R. Need E and R. This is connected to resistor of 10'000 Ohm. The current drawn from the power supply is 0.91A. A voltmeter of internal resistance 10'000 Ohm is connected in parallel to the resistor. The voltmeter reads...
  8. C

    A moving-coil meter, with internal resistance .

    A moving-coil meter, with internal resistance... Homework Statement A moving-coil meter, with internal resistance Rmeter = 15 Ω produces full-scale deflection for a current of 13 mA. Design a voltmeter, as shown below, which can measure voltages in the range 0 - 14 V. What is the required...
  9. B

    Internal resistance of multimeter

    Homework Statement I am taking a class in circuit analysis and am trying to measure the internal resistance of the Radio Shack multimeter. The internal resistance (unknown) is R_x. A battery (with voltage V_s) is available along with a resistor R that has the same order of magnitude of R_x...
  10. R

    What is typical internal resistance of analog voltage meter?

    What is typical internal resistance of a voltage meter on a handheld analog multimeter, and also what is typical resistance on its ammeter?
  11. M

    Finding Resistance from internal resistance and Power in a circuit

    Homework Statement A resistor with resistance R is connected to a battery that has emf 15.0[V] and internal resistance r = 0.38[Ω]. For what two values of R will the power dissipated in the resistor be 78.0 W? Homework Equations P=I2R=(ε2/(R+r)2)R The Attempt at a Solution...
  12. J

    Current problem with emf and internal resistance

    Homework Statement Assuming each battery has internal resistance r = 1.0 Ω, determine the magnitudes and directions of the currents through each resistor shown in the following figure. The batteries have emfs of 1 = 9.0 V and 2 = 12.0 V and the resistors have values of R1 = 15 Ω, R2 = 20 Ω...
  13. A

    Internal Resistance of a Lead Battery

    Anyone knows what is the approx. internal resistance of a lead battery, say, 12V, 20Ah. Thanks
  14. B

    Why battery’s internal resistance decreases with temperature?

    Hi, Does battery internal resistance obey the general resistance-temperature rule? For metal, resistance usually increases with temperature (see wikipedia). For batteries however, its internal resistance decreases with temperature (also see wikipedia). Could anyone explain the...
  15. G

    Short Circuit Current, EMF, Internal Resistance

    Okay so I have conducted an experiment to find the internal resistance of a battery pack by gradient of a graph of voltage against current. All so far okay. I went on to find the EMF also, again all so far okay. Now I need the short circuit current, and I can't find any information anywhere...
  16. H

    Internal Resistance of a Cell?

    Homework Statement A voltmeter is connected across a cell in a circuit containing a switch and a 2Ohm resistor. When the switch is open, the voltmeter reads 12V. When it is closed, the reading is 8V. Find the internal resistance of the cell. Homework Equations I tried to use V=IR - is I...
  17. Biosyn

    How Many Bulbs Are Connected to Match Internal Resistance Voltage Drop?

    Homework Statement A battery has an internal resistance of 0.50 ohm. A number of identical light bulbs, each with a resistance of 15 ohm, are connected in parallel across the battery terminals. The terminal voltage of the batter is observed to be one-half the EMF of the battery. How many bulbs...
  18. A

    Internal Resistance problem when batteries are connected in opposition

    A simple circuit with 2 batteries and a resistor connected in series. The positive terminals are connected to each other via a 4.5 resistor. Their emfs and internal resistances are below. What is the resultant emf? battery 1: ε=6V r=1Ω battery 2: ε=24V r=0.5Ω resistor connecting...
  19. W

    Rate of emf decline and rate of change of internal resistance

    Hello everyone, I am trying to work on this topic as my research. i plan on using a potentiometer but i want to be able to use the resistor (across the test cell) as the load and still be able to obtain two balance points. one for emf, and another for calculating internal resistance as the cell...
  20. L

    What is the internal resistance of the power supply

    A 76 W light bulb with a resistance of 179 Ω is connected to a power supply with a 117 V. What is the internal resistance of the power supply? Express the answer with one decimal place. So my attempt has been this but I'm not exactly sure whether or not so just making sure this would be...
  21. S

    Batteries and Internal resistance

    A 6.0 V battery has an internal resistance r. The measured voltage (emf of the battery) is 6.0 V. When connected to a resistor R the terminal voltage is 5.9 V and the current is 0.18 A. I managed to get a) What is the internal resistance r of the battery? 0.556 ohm as well as b) What is...
  22. A

    Internal resistance of cells in parallel

    I know, as a matter of fact, that the equivalent resistance of three identical cells in parallel is equal to the internal resistance devided by 3. When we are concerning simply 3 equal resistors in parallel, I know that the outcome resistance is what. But when it comes to three cells with...
  23. C

    How do I know what the internal resistance of a battery is in a diagram?

    Homework Statement I am trying to find terminal voltage of the batteries in the circuit shown. Homework Equations V = IR The Attempt at a Solution The solution manual says that it's the battery voltage, v, minus the voltage drawn from the resistance v = I * R. I understand this. I do not...
  24. Femme_physics

    How to treat internal resistance in calculations ?

    Homework Statement http://img217.imageshack.us/img217/654/circuit05.jpg Internal Resistance = 10 ohms (each) RL = 20 ohms R2 = 30 ohms R1 = 50 ohmsA) When the switch is open, calculate I B) When the switch is closed, calculate I Homework EquationsThe Attempt at a Solution First I'll try to...
  25. K

    Calculate emf and internal resistance with two circuits with the same cell

    Homework Statement A cell is connected to a 10.0 Ohm resistor. The pd across the 10.0 Ohm resistor is 10.43 V. A 4.00 Ohm resistor is connected in parallel with the 10.0 Ohm resistor. The pd across the 10.0 Ohm resistor falls to 7.87 V. Calculate the emf and the internal resistance of the...
  26. F

    What is the driving force to increasing the internal resistance of a battery

    What is the "driving force" to increasing the internal resistance of a battery Homework Statement A brand new battery almost have no resistance, but overtime when the internal resistance is great enough, the battery "dies". So my question is, what is causing the internal resistance to...
  27. B

    Find emf and internal resistance of a battery

    Homework Statement When a 60 \Omega resistor and a 120 \Omega are connected in parallel across a battery there is a current of 700 mA flowing through the battery. When the 120 Ohms resistor is disconnected from the circuit the current through the battery drops to 500 mA. What is the emf and the...
  28. U

    Internal resistance, dual power source problem

    Homework Statement An emergency supply consists of a small diesel engine driving an alternator. The output of the alternator is rectified and smoothed to produce DC. This has has to supply 10 amps of 110V emergency lighting and charge a 110V battery of internal resistance 2 ohms, If the...
  29. D

    Internal Resistance of a Battery problem

    Homework Statement A voltmeter whose resistance is 1000 ohms measures the voltage of a worn out 1.5V battery as .9V. What is the internal Resistance Homework Equations The Attempt at a Solution In order to do this, I Solved for the Equiv Resistance of the circuit (leaving in...
  30. E

    Why Does a Current Source Have Internal Resistance in Parallel?

    hello.. this is my first post..forgive me if my question is wrong.. Why does a current source is modeled in such a way that it has its internal resistance in parallel ? Why can't it have its internal resistance in series ? The question may seem awkward , but please answer me.. thanks in advance..
  31. J

    Does different loads produced different internal resistance ?

    hi, if suppose a battery is 100% charged and is capable of delivering 12V. Now if i connect a bulb of 40watts across it then their will be a voltage drop and the internal resistance can be calculated. If the same battery with 100% charge is used with a 80watts bulb then again their will be a...
  32. A

    Internal resistance of a battery

    Ok guys I need help! Its been a while since I last opened a physics workbook and now I'm back to studying to try and further my career and I've come across an internal resistance question that I can't get my head around! A resistance of 10.5 ohms is connected across the terminals of a battery...
  33. T

    Analogies for internal resistance and emf

    Hi! I'm trying to fully grasp why the potential drops when an internal resistance is present in a source of emf. At first I thought that yes it would be harder to "push" the charges to the higher potential, but once there, why shouldn't the higher potential be the same as before? Just as if a...
  34. P

    Solving for Vemf and Internal Resistance

    When a battery is connected to a 110.-ohm resistor, the current is 3.98 A. When the same battery is connected to a 400.-ohm resistor, the current is 1.11 A. Find the emf supplied by the battery and the internal resistance of the battery. Equations: Vemf = i*R I'm not sure how...
  35. P

    Internal resistance, emf UNCERTAINTIES

    Homework Statement "From your graph, calculate the EMF and internal resistance of your cells. Include uncertainties in your calculations" Now I know how to work out the emf and int. resistance, but I am just not sure about how to incorporate uncertainties. Homework Equations y = mx +...
  36. jegues

    Engineering Interface circuit for a device with internal resistance

    Homework Statement You are given a device with which to operate with an input resistance of 50 W. The device requires 9 V to operate. However, the only available power supply is a 12 V source. Part A:Using only resistors, design an interface circuit to lower the 12 V to 9 V for operating...
  37. A

    How Do I Find the Internal Resistance in this Circuit?

    Homework Statement http://img408.imageshack.us/img408/6537/screenshot20100808at134.png Homework Equations The Attempt at a Solution I redrew the circuit as follow: http://img293.imageshack.us/img293/6247/screenshot20100808at135.png Is this correct (or even useful in the first place)...
  38. J

    Does Battery Capacity depend on Internal Resistance?

    Just like the title, does battery capacity depend on internal resistance? I know it does depend on the temperature and the chemical structure of the battery, but does it also depend on internal resistance? If so, how dependent are batteries on internal resistance? Also, what is the...
  39. W

    Does Battery Internal Resistance Vary with External Resistance?

    Is the internal resistance of the battery or other source is variable or not? without discharging . Is it depend upon on the external resistance?
  40. L

    Flashlight battery - internal resistance?

    Homework Statement does a flashlight battery have an internal resistance? explain. this problem is for my lab, and we are farther ahead in lab than in lecture. so i haven't actually learned this material yet. Homework Equations i'm not really sure. R=∆V/I also, -VB + VR + VM +...
  41. D

    Terminal voltage and internal resistance

    A battery labeled 12.0 V supplies 1.90 A to a 6.00 ohm resistor A) what is the terminal voltage of the battery? B) What is its internal resistance V = 12.0 R = 6.00 I = 1.90 I think i am to use V = emf - IR for terminal voltage right? however i do not know how to get emf, and IR...
  42. K

    DC Circuits Question (internal resistance)

    Homework Statement Determine the magnitudes and directions of the currents through R1 and R2 in Fig. 19-47, where R1 = 37 and R2 = 16 . Figure 19-47 (image attached) V1 = 9.0 V V3 = 6.0 V R1 = 37 \Omega R2 = 16 \Omega Homework Equations V = IR The Attempt at a Solution...
  43. S

    Determining the Internal Resistance of Battery X

    Homework Statement Two almost identical lead-acid accumulator batteries, X and Y, are connected with opposing polarities in a circuit which includes an ammeter, an ideal millivoltmeter and a resistor R as shown in figure below. When S1 is closed with S2 left open, the millivoltmeter reads 50...
  44. A

    Maximum Power Dissipation at Internal Resistance Proof

    Homework Statement My physics teacher (i'm in year 12) set me a "challenge" to prove a graph in our textbook, which shows Power against Resistance, with a local maximum where R = internal resistance, r. He told me i'd need to use differentiation, P = I^{2}.R and said that I was right in...
  45. U

    How Do You Calculate Battery Internal Resistance from Load Conditions?

    Homework Statement I have been stuck on the following problem for 2 days now, can anyone help? The p.d. at the terminals of a battery is 25V when no load is connected and 24V when a load taking 10A is connected. Determine the internal resistance of the battery... Thanks Homework...
  46. J

    Current through a voltmeter with internal resistance

    Homework Statement You have a power supply of 10 V. It is connected in series to a 2 ohm resistor and a 5 ohm resistor. You take the voltage across the 5 ohm resistor with a voltmeter that has an internal resistance of 3 ohms. What is the current through the voltmeter?Homework Equations The...
  47. E

    Solar Cell Physics Coursework (Calculating Internal Resistance)

    Basically I want to Calculate the internal resistance of a solar cell. I set up a circuit with a voltmeter across the solar cell and an ammeter and variable resistor in series with the solar cell. The variable resistor is the load. Image at...
  48. J

    Determining EMF and Internal Resistance

    Basically I have been given this question: A battery of unknown EMF and internal resistance is connected in series with an ammeter and a resistance box. The current was 2.0A when R= 4.0 Ohms and 1.5A when R= 6.0 Ohms. Calculate the EMF and internal resistance. I feel you may have to...
  49. C

    Voltage and Current in circuits( paral. and series) involv. internal resistance

    Homework Statement Two resistors R1= 132 ohms and R2= 56 ohms are connected to a 6.00 V battery with an internal resistance of 5.00 ohms. Find the voltage across R2 and the current through R1 a) if the resistors are connected in series, and b) if they are connected in parallel. Homework...
  50. J

    Circuit for determining the internal resistance of a dry cell

    What sort of circuit would I have to set up to figure out the internal resistance of a dry cell? Also, what would i need to be measuring and doing etc, to find this internal resistance? Thanks, Jack.
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