what is internal resistance?

Answer 1

Another word for it is IMPEDANCE. You can see an article redirected from internal resistance to Output Impedance here"
http://en.wikipedia.org/wiki/Internal_resistance

Answer 2

Suppose we have an accumulator of 2V.

When the accumulator is not connected to any external circuit, a voltmeter will measure the potential difference across the battery terminals as 2V.

This is called the EMF of the battery.

Suppose we connect the battery to a resistance of 2 ohm,
using Ohm’s law we expect the current to be 2/2 = 1 ampere.

But in practice, it will be less than 1 A, say 0.9 A.

This shows, the resistance is greater than 2 ohm.

If the resistance were 2.22 ohm then the current will be
(2/ 2.22) = 0.9 A.

Where is this excess resistance of 0.22 ohm?

Externally, we have connected exactly 2 ohm.

Therefore, inside the battery, the chemicals give an additional resistance of 0.22 ohm.

This is the internal resistance of the battery.

The potential across the battery will not be now 2V, It will be only 1.8 V. This again confirms the internal resistance, because 0.9 x 0. 22 (current x resistance) = 0.2 V is dropped inside the battery.

The resistance offered by the source internally is called internal resistance.

The internal resistance is not a constant one and it depends upon the external resistance used.

Answer 3

The output impedance, source impedance, or internal impedance of an electronic device is the opposition exhibited by its output terminals to the flow of an alternating current (AC) of a particular frequency as a result of resistance, inductance and capacitance.

The impedance at DC (frequency of 0) is the same as the resistance component of the impedance and is termed output resistance.

It is important to realize that no real device (battery, generator, amplifier) is a perfect source; all have an internal impedance, though this may have negligible effect, depending on the load.

Depending on perspective, this impedance appears in series with a perfect voltage source, or in parallel with a perfect current source (see: Thevenin's theorem, Norton's theorem).

For example, a preamplifier with 100Ω output impedance means the output voltage signal appears to be in series with a 100Ω resistor
Measurement
The source resistance of a purely resistive device can be experimentally determined by increasingly loading the device until the voltage across the load (AC or DC) is 1/2 of the open circuit voltage. At this point, the load resistance and internal resistance are equal.

It can more accurately be described by keeping track of the voltage versus current curves for various loads, and calculating the resistance from Ohm's law. (The internal resistance may not be the same for different types of loading, especially in devices like chemical batteries.)

The generalized source impedance for a reactive (inductive or capacitive) source device is more complicated to determine, and is usually measured with specialized instruments, rather than taking many measurements by hand.


[edit] Audio amplifiers


The real output impedance (Zsource) of a power amplifier is usually less than 0.1Ω, but this is rarely specified. Instead the value is "hidden" within the damping factor parameter, which is:


Solving for Zsource,


gives the small source impedance (output impedance) of the power amplifier. This can be calculated from the Zload of the loudspeaker (typically 2, 4, or 8 ohms) and the given value of the damping factor.

Generally in audio and hifi, the input impedance of components is several times (technically, more than 10) the output impedance connected to them. This is called impedance bridging or voltage bridging.

In this case, Zload>> Zsource, DF > 10

In video, RF, and other systems, impedances of inputs and outputs are the same. This is called impedance matching or a matched connection.

In this case, Zsource = Zload, DF = 1/1 = 1

The output impedance is not the same as the rated output impedance. A power amplifier may have a rated impedance of 8 ohms, but this does not mean the output impedance is of that value. The rated output impedance is simply that impedance into which the amplifier can deliver its maximum amount of power without failing.


[edit] Batteries
Internal resistance is a concept that helps us model the complex chemical reactions that occur inside a battery. It is impossible to directly measure the internal resistance of a battery, but it can be calculated from current and voltage data measured from a circuit. When a load is applied to a battery the internal resistance can be calculated from the following equations:



or



where

RB is the internal resistance of the battery

VS is the battery voltage without a load

V is the battery voltage with a load

RL is the total resistance of the circuit

I is the total current supplied by the battery

Answer 4

Internal resistance is a fictitious resistance that is useful in calculations.

A perfect battery would have a fixed voltage between its terminal regardless of how much current it supplied. But real batteries do not behave like this - as the current rises the voltage drops very slightly. Provided this drop is linear (i.e. the change in voltage is just some constant times the change in current) then it can be treated as though there is a resistance in series with the battery but internal to it. Then when a current flows some of the voltage between the terminals is actually dropped across the resistor rather than the active part of the battery itself. There is NO SUCH RESISTOR, its just a useful calculation tool.

At large currents, the relationship between the change in current and change in voltage is not linear, and the method does not work.

Answer 5

If you short circuit the battery the current is not infinite. Therefore the internal model of the battery is an ideal voltage source with internal resistance in series. The voltage of the voltage source is the measured voltage of the open battery. So when you short circuit the battery the current flowing will be open voltage divided by the internal resistance. Therefore internal resistance is the ratio of open voltage battery over the short circuit current. The concept is very useful in looking how good is your battery including car battery since the battery in fact never looses the voltage (it is given by chemical attraction of atoms) however old battery increases internal resistance. To see the goodness of your car battery the car mechanics measure the short circuit current. In this way you can also see how good are ordinary batteries like AA or AAA etc.

Answer 6

u know that,
The current flows from the +ve of the battery to the negative of the battery.
but when current flows in such a manner , in the battery |I
there is a gap(as u cud see in any circuit diagram).
that gap is made of electrolyte of the battery.
hence to complete the circuit, current flows thro' the electrolyte from negative to the positive terminals.
during this process , some resistance is offered by the electrolyte of the cell.
This is called as INTERNAL RESISTANCE.
hope u understand my explanation.