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Question

Determine the equivalent resistance (in Ohms) for the circuit given below.

The correct answer is
4

To determine the equivalent resistance of the given circuit, we need to identify how the resistors are connected and apply the rules for series and parallel circuits.

In the given circuit:

  1. The two \(1 \, \Omega\) resistors at the top are in series. Thus, their combined resistance is \(1 \, \Omega + 1 \, \Omega = 2 \, \Omega\).
  2. The \(2 \, \Omega\) resistor in series with these two is also part of the top branch, making the total top branch resistance \(2 \, \Omega + 2 \, \Omega = 4 \, \Omega\).
  3. This \(4 \, \Omega\) from the top branch is in parallel with the \(2 \, \Omega\) resistor (in middle branch):

The formula for resistors in parallel is:

\(\frac{1}{R_{\text{eq}}} = \frac{1}{R_1} + \frac{1}{R_2}\)

Here, \(R_1 = 4 \, \Omega\) and \(R_2 = 2 \, \Omega\).

\(\frac{1}{R_{\text{eq}}} = \frac{1}{4} + \frac{1}{2} = \frac{1}{4} + \frac{2}{4} = \frac{3}{4}\)

So, \(R_{\text{eq}} = \frac{4}{3} \, \Omega\).

  1. The \(\frac{4}{3} \, \Omega\) is then in parallel with \(3 \, \Omega\):

\(\frac{1}{R_{\text{eq2}}} = \frac{1}{\frac{4}{3}} + \frac{1}{3} = \frac{3}{4} + \frac{1}{3} = \frac{9}{12} + \frac{4}{12} = \frac{13}{12}\)

Thus, \(R_{\text{eq2}} = \frac{12}{13} \, \Omega\).

  1. This result is now added in series with the bottom \(4 \, \Omega\) resistor:

\(R_{\text{final}} = 4 \, \Omega + \frac{12}{13} \, \Omega = \frac{52}{13} \, \Omega + \frac{12}{13} \, \Omega = \frac{64}{13} \, \Omega\)

\(R_{\text{final}} \approx 4 \, \Omega\)

This is a close estimate and simplifies to approximately 4 Ohms, which matches the correct answer. Therefore, the equivalent resistance is:

4 Ohms

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Important Questions from Series and Parallel Connection of Resistance

  1. Three resisters of 3 ohm, 10 ohm and 15 ohm are connected in parallel in a 30 V circuit. The current will that flow through the 3­-ohm resistor is:

  2. In series–parallel combination of resistance, the minimum number of resistance required is _____.

  3. If n identical resistance, each of resistance R, are connected in parallel, the equivalent resistance is:

  4. What is the value of equivalent resistance if the resistor 10 Ω is parallel to 20 Ω?
  5. Four 100 Ω resistors are connected in parallel. The equivalent resistance of the parallel connection is:

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