A source of electromotance \(6 \mathrm{~V}\) and internal resistance \(2 \Omega\) has in parallel across its terminals (a) a \(2 \Omega\) resistor and (b) a series combination of 1 and a \(4 \Omega\) resistor. A further \(1 \Omega\) resistor \(R\) is connected across the \(4 \Omega\) resistor. Find the current in \(R\) using Thévenin's theorem.

Short Answer

Expert verified
Answer: The current in the 1Ω resistor (R) is \(\frac{81}{46} A\).

Step by step solution

01

Draw the circuit diagram

Firstly, draw the circuit diagram as per the given information. The voltage source (6V) and internal resistance (2Ω) are given. The terminals (a) and (b) have a 2Ω resistor in parallel, followed by a series combination of a 1Ω resistor and a 4Ω resistor. Finally, the 1Ω resistor (R) is connected across the 4Ω resistor.
02

Thévenin Voltage (Vth)

To find the Thévenin voltage, we must first remove the 1Ω resistor (R) from the circuit. Then, calculate the voltage across the 4Ω resistor. We can first calculate the equivalent resistance of the parallel combination of 2Ω and a series combination of 1Ω and 4Ω resistors. Let Rp be the equivalent parallel resistance, \( Rp = \frac{ (2 + 4 + 1) * 2 }{ (2 + 4 + 1) + 2} = \frac{14}{9}Ω \) Now, the total resistance in the circuit (RT) will be the internal resistance (2Ω) and Rp, \( RT = 2 + \frac{14}{9} = \frac{32}{9}Ω \) Now, we calculate the total current (IT) passing through the circuit using Ohm's law, \( IT = \frac{V}{RT} = \frac{6}{\frac{32}{9}} = \frac{27}{16} A \) Now, we can find the current passing through the parallel combination (IA), \( IA = IT = \frac{27}{16} A \) So, the voltage across the 4Ω resistor (Vth), \( Vth = IA * 4Ω = \frac{27}{16} * 4 = \frac{27}{4}V \)
03

Thévenin Resistance (Rth)

Now, we need to find the Thévenin resistance (Rth). Remove the voltage source and short circuit the terminals. The Thévenin resistance will be the equivalent resistance between the two terminals (a and b). The resistance across the terminals is a parallel combination of 2Ω and the series combination of 1Ω and 4Ω. Calculate the equivalent parallel resistance (Rp) as done in Step 2. Then, \( Rth = \frac{14}{9}Ω \)
04

Find the current in 1Ω resistor (R) using Thévenin's theorem

Now, we have the simplified circuit with Vth, Rth, and the 1Ω resistor. To find the current in the 1Ω resistor (IR), use Ohm's Law. Total Resistance RT' = Rth + R \( RT' = \frac{14}{9} + 1 = \frac{23}{9}Ω \) By applying Ohm's law, \( IR = \frac{Vth}{RT'} = \frac{\frac{27}{4}}{\frac{23}{9}} = \frac{81}{46} A \) Hence, the current in the 1Ω resistor (R) is \(\frac{81}{46} A\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Electrical Circuit Analysis
Understanding electrical circuits is at the heart of electrical engineering and physics. It's about figuring out how electrical currents move and how they behave under different conditions.

Thévenin's theorem is a brilliant concept used in electrical circuit analysis. It simplifies complex networks to a basic two-component circuit with just a voltage source and a single resistor. This makes it much easier to analyze the circuit and predict how it will behave, especially when looking at the current passing through a specific component, like the resistor R in our given problem.

An important step in the process is drawing the circuit diagram. Visualization helps us break down the components and their arrangements. Plus, it's crucial to respect the rules when identifying series and parallel connections, as they affect the overall resistance and the flow of current through the network.
Equivalent Resistance
When you're dealing with resistors in circuits, it pays off big time to understand equivalent resistance. It's like a shortcut that lets you replace a bunch of resistors with just one that has the same effect. Super handy, right?

In the provided exercise, we tackle a somewhat tricky setup involving parallel and series components. The key to cracking this is to calculate the equivalent resistance for these combinations. We use formulas tailored to these connections. For resistors in series, just add their resistances. For parallel pals, the formula is a bit more complex, as you've seen with the term \( Rp = \frac{ (2 + 4 + 1) * 2 }{ (2 + 4 + 1) + 2} \).

Remember, equivalent resistance affects the total current running through the circuit, so getting this right is a big deal for accurate analysis.
Ohm's Law
Ohm's Law is like the ABCs of electrical circuits. It's the fundamental principle that tells us there's a straight-up relationship between voltage, current, and resistance. If you know two of them, you can figure out the third.

In technical terms, the law states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance. Mathematically, it's elegantly simple: \(\frac{V}{R} = I\).

We applied this law to find the current in the 1Ω resistor in the given exercise. With the Thévenin voltage (Vth) and the total resistance (RT'), the law guided us to the solution. Mastering Ohm's Law opens up a world of analysis and understanding in electrical circuits, making complex problems like these quite manageable.

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Most popular questions from this chapter

A 45 ampere-hour battery will supply 45 A for \(1 \mathrm{~h}, 2 \mathrm{~A}\) for \(22.5 \mathrm{~h}\), etc. If such a battery has an electromotance of \(12 \mathrm{~V}\), find (a) the total charge which can be supplied, (b) the total energy available, (c) how long the sidelights of a car could be operated if they consumed \(24 \mathrm{~W}\), (d) how long the battery could operate the starter motor taking \(135 \mathrm{~A}\). Assume that the potential difference at the terminals is \(12 \mathrm{~V}\) and remains at this value until complete discharge.

In a Wheatstone bridge network, the galvanometer is replaced by a battery of the same electromotance 8 as the one already present. If the resistances of all the arms and of both batteries are equal to \(R\), find the currents in the various branches.

A twin cable carries current between A and \(\mathrm{B}, 5\) miles apart. It is known to have one fault, i.e. a breakdown in the insulation between the two conductors, but not necessarily a short-circuit. A potential difference of \(200 \mathrm{~V}\) maintained across the ends at A produces a potential difference of \(50 \mathrm{~V}\) across the ends at B, while \(200 \mathrm{~V}\) across B produces \(20 \mathrm{~V}\) across \(\mathrm{A}\). Locate the fault.

Three of the four arms of a Wheatstone bridge network are of \(40 \Omega\), the fourth is \(41 \Omega\) and the resistance of the detector is \(20 \Omega\). If the driving source has an electromotance of \(2 \mathrm{~V}\) and negligible internal resistance, find the current through the detector using Kirchhoff's laws.

A d.c. source has an electromotance of \(120 \mathrm{~V}\) and a negligible internal resistance. If \(n\) cells, each of electromotance \(2.1 \mathrm{~V}\) and internal resistance \(0.1 \Omega\), are to be charged from this source with a charging current of \(3 \mathrm{~A}\), find the series resistance necessary. If \(n=20\), what proportion of energy delivered by the source is wasted as heat? Find also the potential difference across the 20 cells.

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