{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

supch02 - CHAPTER 2 BASIC LAWS List of topics for this...

Info icon This preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
CHAPTER 2 - BASIC LAWS List of topics for this chapter : Ohm's Law Nodes, Branches, and Loops Kirchoff's Laws Series and Parallel Resistors Wye-Delta Transformations Applications OHM'S LAW Ohm's law states that the voltage across a resistor is directly proportional to the current flowing through the resistor. R i v = Problem 2.1 Given an incandescent light bulb rated at 75 watts and 120 volts, find the “hot” resistance and “cold” resistance of the light bulb. An incandescent light bulb is the most common source of light produced by electrical energy. A current is made to flow through a wire, called a filament. Since this wire has resistance, the wire absorbs power, so much so that it “glows” and gives off light. Ratings on these types of light bulbs are for steady-state operating conditions. So, we have 40 25 120 75 V P I = = = amps 192 40 25 120 I V R = = = ohms Hence, the “hot” resistance is 192 ohms . Most wire has what we call a positive thermal resistance characteristic; that is, as the wire temperature increases, the resistance increases. It is sufficient to say at this time that the “cold” resistance is less than 192 ohms . Problem 2.2 Solve for v, i, and R for the following : (a) 10 R = ohms and 2 i = amps (b) 5 R = ohms and 20 v = volts (c) 10 v = volts and 5 i = amps (d) 3 i = amps and 20 v = volts
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
(a) = v volts 20 (b) = i amps 4 (c) = R ohms 2 (d) = R ohms 667 . 6 NODES, BRANCHES, AND LOOPS A branch represents a single element, such as a voltage source or a resistor. A node is the point of connection between two or more branches. A loop is any closed path in a circuit. Problem 2.3 [2.7] Determine the number of branches and nodes in the circuit in Figure 2.1. Figure 2.1 There are 7 elements, 1 dependent current source, 1 independent voltage source, and 5 resistors, which implies that there are 7 branches . There are 5 nodes as indicated by the dark circles and dark lines in the circuit below. 5 5 10 V 5 5 10 V
Image of page 2
Problem 2.4 Identify all the nodes, branches, and independent loops in Figure 2.1. Figure 2.1 There are 8 nodes , as indicated by the dark circles and dark lines in the circuit below. There are 14 branches , 4 independent voltage sources and 10 resistors. There are 7 independent loops . Check. Does this satisfy the fundamental theorem of network topology? b = l + n – 1 = 7 + 8 – 1 = 14 YES!
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Problem 2.5 In Figure 2.0 , is there a loop? How many nodes are there? A loop is any closed path; therefore it is easy to say there is no loop. However, there really is a loop since there is an infinite resistance connecting the end terminals together. Thus, there is one loop . There are three nodes , one where the voltage source and resistor join and the two at the output terminals. In addition, there are three branches . The voltage source, the resistor, and the infinite resistance. Thus, the fundamental theorem of network topology is satisfied.
Image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern