Thevenin's Theorem La Report,

Pages: 4 (669 words) Published: April 27, 2012

EXPERIMENT NO. 10
Thevenin’s Theorem

Objectives:

1. To verify the Thevenin’s theorem through an experiment. 2. To find the Thevenin’s resistance RTH by various methods and compare values.

Equipment:

Resistors, DMM, breadboard, DC power supply, and connecting wires.

Theory:
Thevenin theorem states that any linear two-terminal circuit can be replaced by an equivalent circuit consisting of a voltage source VTH in series with a resistance RTH where

* VTH is the open-circuit voltage at the terminals, and
* RTH is the equivalent resistance seen thru the terminals provided that all the independent sources are turned off.

Finding VTH:

Determining the output voltage Vab in open-circuit condition (no load resistor meaning infinite resistance). This is known as the Thevenin voltage VTH. * i.e. VTH = Vab = VOC (open-circuit voltage)

Finding RTH:

There are different methods to find value of RTH as described below.

1. Method A:

(By measuring ISC – short-circuit current)
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Short the points ‘a’ and ‘b’, then measure the short-circuit current Isc using an ammeter. Calculator RTH as follows

RTH = VTH/ ISC

Method 2:

(By measuring the equivalent resistance)

Remove all sources from the circuit, i.e. replace all voltage sources with a short-circuit and current sources with an open-circuit. Then with the help of a multimeter find the resistance between the points ‘a’ and ‘b’, denoted by Req.

RTH = Req

Method 3:

(By applying known voltage and measuring source current).

We can also find RTH by applying a known voltage to the circuit between points ‘a’ and ‘b’, then measuring the current from the voltage source. Suppose 1 Vdc is applied as the test voltage then,

RTH = Vtest / I
4. Method 4:

(By inserting two different resistors and measuring current) There is another method to find the value of RTH, by inserting two different loads between points ‘a’ and ‘b’ i.e....