# 23 Lecture

## Thevenin's Theorem and examples

Thevenin's theorem is an important concept in circuit theory that allows us to simplify complex circuits into simpler circuits, making it easier to analyze and understand them.

## Important Mcq's Midterm & Finalterm Prepration Past papers included

What is Thevenin's theorem?

a. A theorem that simplifies complex circuits to a single voltage source and series resistance.

b. A theorem that simplifies complex circuits to a single current source and parallel resistance.

c. A theorem that calculates the current flowing in a circuit.

Solution: a

Who developed Thevenin's theorem?

a. James Clerk Maxwell

b. Charles Wheatstone

c. Leon Charles Thevenin

Solution: c

What is the Thevenin resistance?

a. The equivalent resistance of a circuit when all voltage sources are turned off and all current sources are shorted.

b. The voltage between two points in a circuit when no current is flowing through the circuit.

c. The equivalent resistance of a circuit when all voltage sources are turned on and all current sources are open.

Solution: a

How can we determine the Thevenin voltage of a circuit?

a. By selecting two points in the circuit and assuming that all components to the right of these points are removed, leaving only the components to the left.

b. By selecting two points in the circuit and assuming that all components to the left of these points are removed, leaving only the components to the right.

c. By measuring the voltage at a single point in the circuit.

Solution: a

How can we determine the Thevenin resistance of a circuit?

a. By selecting two points in the circuit and assuming that all components to the right of these points are removed, leaving only the components to the left.

b. By selecting two points in the circuit and assuming that all components to the left of these points are removed, leaving only the components to the right.

c. By measuring the resistance of a single component in the circuit.

Solution: a

Can Thevenin's theorem be used for AC circuits?

a. Yes

b. No

Solution: a

Can Thevenin's theorem be used for DC circuits?

a. Yes

b. No

Solution: a

What is the equivalent resistance of a circuit with only resistors in series?

a. The sum of all the resistances.

b. The reciprocal of the sum of the reciprocals of all the resistances.

c. The difference between the highest and lowest resistance.

Solution: a

What is the equivalent resistance of a circuit with only resistors in parallel?

a. The sum of all the resistances.

b. The reciprocal of the sum of the reciprocals of all the resistances.

c. The difference between the highest and lowest resistance.

Solution: b

What is the advantage of using Thevenin's theorem?

a. It allows us to simplify complex circuits into simpler circuits, making it easier to analyze and understand them.

b. It allows us to increase the voltage in a circuit.

c. It allows us to decrease the resistance in a circuit.

Solution: a

## Subjective Short Notes Midterm & Finalterm Prepration Past papers included

What is Thevenin's theorem?

Answer: Thevenin's theorem states that any complex circuit can be simplified to a single voltage source and a series resistance.

Who developed Thevenin's theorem?

Answer: Thevenin's theorem was developed by Leon Charles Thevenin, a French engineer.

What is the Thevenin voltage?

Answer: The Thevenin voltage is the voltage between two points in a circuit when no current is flowing through the circuit.

What is the Thevenin resistance?

Answer: The Thevenin resistance is the equivalent resistance of a circuit when all voltage sources are turned off and all current sources are shorted.

How can we determine the Thevenin voltage and resistance of a circuit?

Answer: We can determine the Thevenin voltage and resistance by selecting two points in the circuit and assuming that all components to the right of these points are removed, leaving only the components to the left.

What is the simplified circuit that results from applying Thevenin's theorem?

Answer: The simplified circuit that results from applying Thevenin's theorem consists of a single voltage source and a series resistance.

Can Thevenin's theorem be used for AC circuits?

Answer: Yes, Thevenin's theorem can be used for both DC and AC circuits.

What is the advantage of using Thevenin's theorem?

Answer: The advantage of using Thevenin's theorem is that it allows us to simplify complex circuits into simpler circuits, making it easier to analyze and understand them.

What is the equivalent resistance of a circuit with only resistors in series?

Answer: The equivalent resistance of a circuit with only resistors in series is the sum of all the resistances.

What is the equivalent resistance of a circuit with only resistors in parallel?

Answer: The equivalent resistance of a circuit with only resistors in parallel is the reciprocal of the sum of the reciprocals of all the resistances.

### Thevenin's Theorem and examples

Thevenin's theorem is an important concept in circuit theory that allows us to simplify complex circuits into simpler circuits, making it easier to analyze and understand them. It is named after its inventor, Leon Charles Thevenin, a French engineer who developed this theorem in the late 19th century. This article will provide an overview of Thevenin's theorem, explain how it works, and provide examples of its application in circuit theory. Thevenin's theorem states that any complex circuit can be simplified to a single voltage source and a series resistance. The voltage source is called the Thevenin voltage, and the series resistance is called the Thevenin resistance. This simplified circuit is equivalent to the original complex circuit, meaning that it will produce the same output for any given input. To apply Thevenin's theorem, we must first identify the circuit that we want to simplify. We then select two points in the circuit and assume that all components to the right of these points are removed, leaving only the components to the left. We can then determine the voltage between these two points, which is the Thevenin voltage. We also determine the resistance between these two points, which is the Thevenin resistance. The Thevenin voltage is the open-circuit voltage, meaning that no current is flowing through the circuit. The Thevenin resistance is the equivalent resistance of the circuit when all voltage sources are turned off and all current sources are shorted. Once we have determined the Thevenin voltage and resistance, we can simplify the circuit by replacing all components to the left of the two points with a single voltage source with the value of the Thevenin voltage, and a series resistance with the value of the Thevenin resistance. Let's look at an example to understand how Thevenin's theorem works in practice. Consider the circuit shown below: Thevenin's Theorem Example Circuit We want to simplify this circuit using Thevenin's theorem. We first select the two points where we want to apply the theorem, which are shown in red. We then remove all components to the right of these points and determine the Thevenin voltage and resistance. To find the Thevenin voltage, we first find the open-circuit voltage between the two points, which is the voltage across the 8-ohm resistor. Using Ohm's law, we can calculate this voltage as: Voc = I x R = 0.5 x 8 = 4 volts To find the Thevenin resistance, we first remove all voltage sources and replace them with short circuits, and we remove all current sources and replace them with open circuits. This leaves us with the following circuit: Thevenin's Theorem Example Circuit Without Sources We can now calculate the equivalent resistance between the two points. To do this, we can combine the 2-ohm and 6-ohm resistors in parallel, which gives us a total resistance of 1.5 ohms. We can then combine this with the 3-ohm resistor in series, which gives us a total resistance of 4.5 ohms. Therefore, the Thevenin resistance is 4.5 ohms. Now that we have determined the Thevenin voltage and resistance, we can simplify the original circuit by replacing all components to the left of the two points with a single voltage source of 4 volts and a series resistance of 4.5 ohms,