Internal Resistance Formula

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Introduction

The relationship between internal resistance denoted by r and emf denoted by e of a cell is given by that are:

e = I (r + R)

Where we can notice that the term denoted by the letter e = EMF known as the electromotive force of Volts written as: I = current which  is denoted by A the letter that is R = Load resistance and the letter which is r is the internal resistance of a cell measured in ohms.

On rearranging the above equation we get the following:

That is e = IR + Ir  or, e = V + Ir


The Formula of Internal Resistance

In the above equation, we can say that the letter  V is the potential difference terminal across the cell when the current which is denoted by I is flowing through the circuit.

We can note: The emf denoted by letter e of a cell is always greater than the potential difference generally terminal across the cell.

Example: 1 that is the potential difference which is across the cell when no current flows through the circuit that is 3 V. When the current devoted by I = 0.37 that is ampere is flowing that is the terminal potential difference which falls to 2.8 Volts. Determine the internal resistance denoted by letter r of the cell?

Solution:

That is e = V + Ir

Or we see e – V = Ir

Or this (e – V)/I = r

Therefore we see that r = (3.0 – 2.8)/0.37 = 0.54 Ohm.

Now due to the Internal Resistance which is of the cell that is the electrons moving through the cell which turns some of the electrical energy to heat energy. Therefore we see that the potential difference is available to the rest of the circuit that is:

That is V = E which means EMF of cell – Ir that is the p.d. across the internal resistor

The electromotive force that is denoted by e or the e.m.f. is the energy that is generally provided by a cell or battery per coulomb of charge passing through it. So we can say that it is measured in volts that is V. It is said to be equal to the potential difference which is across the terminals of the cell when no current is flowing.

ε=E/Q

  • We can say that e = electromotive force in volts, V

  • And then E = energy in joules, J

  • Then letter Q = charge in coulombs, C

The batteries and cells have an  internal resistance denoted by letter r which is measured in ohm’s denoted by W. When the flow of electricity is around a circuit the internal resistance that is of the cell itself resists the flow of current and so thermal that is said to be heat that is the energy is wasted in the cell itself.

ε=I(R+r)

  • The letter e = electromotive force in volts, V

  • The letter I = current in amperes, A

  • The letter R = resistance of the load in the circuit in ohms, W

  • The letter r = internal resistance of the cell in ohms, W


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Here the rearrange of the the above equation is:

ε=IR+Ir

and then to the following: 

ε=V+Ir

In this equation we know that the letter V appears which is the terminal potential difference that is generally measured in volts that is V. This is the potential difference which is said to be across the terminals of the cell when current is flowing in the circuit, that is it is always less than the e.m.f. of the cell.

We Can Say For Example:

1. We can say that the p.d. That is across the terminals of a cell is 3.0 volts when it is not connected to a circuit and no current is flowing. Here when the cell is said to be connected to a circuit and a current of  0.37 A is flowing the terminal p.d. That generally falls to 2.8 V. we can say that what is the internal resistance of the cell?

A graph that is of a terminal which is of the p.d. against current

So we can say that if we plot a graph of terminal potential difference that is denoted by V against the current in the circuit that is denoted by I we now get a straight line with a negative gradient.


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We can here say that to them generally rearrange the e.m.f. equation which is from above to match the general expression which is for a straight line that is we can say y = mx +c.


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We can note that it is from the red boxes that is above: 

  • The intercept which is said to be on the y-axis is equal to the e.m.f. That is of the cell

  • The gradient which is said to be of the graph is equal to -r where r is the internal resistance that is of the cell.

We can say that the physics net Site Search.


Internal Resistance of a Cell Formula

The electromotive force that is  EMF is an unfamiliar concept which is to most of the students. These things are closely linked to the more familiar concept which is of voltage. The understanding of the difference that is  between these two and what EMF that generally means gives us the tools we need to solve many problems in physics as well as in electronics. It will also introduce the concept of the internal resistance of a battery. Here again we can say that EMF tells about the voltage of the battery which is without the internal resistance reducing the value. This topic is said to explain the emf formula with examples. So again we can see that let us learn it.

The electromotive force already is said to be defined as the potential difference which is across the terminals of the battery that is we can say when no current is flowing through it. This is said to not seem like this as it would make a difference but we can say that every battery has internal resistance. We can say that it is similar to the ordinary resistance that reduces current in a circuit, but it exists within the battery itself.

There is no current flowing through the cell that is said to be then this internal resistance which will not change anything because there is no current for it to slow down. 

FAQ (Frequently Asked Questions)

1. Explain How You Calculate the Internal Resistance of a Cell?

Ans: A graph which is said to be of a terminal that is the p.d. against current

  1. Here we see that the intercept which is on the y-axis is said to be equal to the e.m.f. of the cell.

  2. The gradient of the graph is said to be equal to -r which is where r is the internal resistance that is said to be of the cell.

2. Explain What is the Internal Resistance of a Cell and Derive its Equation?

Ans: we can see that the equation V = ε – Ir. So, V = ε – Ir, where the letter V is the said to be the potential difference which is across the circuit and ε is the emf that is the letter I is the current flowing through the circuit, r is internal resistance. 

3. Explain What Causes Internal Resistance?

Ans: We can say that the sulfation and grid corrosion which are the main contributors to the rise of the internal resistance will lead the acid. The temperature which also affects the resistance that is the heat lowers it and cold raises it. We can say that heating the battery will momentarily lower the internal resistance to provide extra runtime.

4. Explain What is the Formula Resistance?

Ans: we can here say that the resistance formula which is as follows: the Resistance = the drop in the voltage that is across a resistor and the current flowing that is through a resistor. The letter that is R = IV. R = resistance that is the Ohms, Ω) and the letter V = voltage difference which is between the two ends of a resistor Volts that is denoted by letter  V.