Skip to main content

KIRCHHOFF'S LAW


Gustav Robert Kirchhoff (12 March 1824 – 17 October 1887) was a German physicist who contributed to the fundamental understanding of electrical circuits, spectroscopy, and the emission of black-body radiation by heated objects. He coined the term "black body" radiation in 1862, and two sets of independent concepts in both circuit theory and thermal emission are named "Kirchhoff's laws" after him, as well as a law of thermochemistry. The Bunsen–Kirchhoff Award for spectroscopy is named after him and his colleague, Robert Bunsen.


Kirchhoff's Lawsen.wikipedia.org 
Kirchhoff's circuit laws are two equalities that deal with the conservation of charge and energy in electrical circuits, and were first described in 1845 by Gustav Kirchhoff. Widely used in electrical engineering, they are also called Kirchhoff's rules or simply Kirchhoff's laws.


These goals are very important.  If you can't write KVL equations and solve them, you may well be lost when you take a course in electronics in a few years.  It will be much harder to learn that later, so be sure to learn it well now.  (And, if you need to review the concept of voltage)

This fundamental law results from the conservation of charge. It applies to a junction or node in a circuit -- a point in the circuit where charge has several possible paths to travel. In Figure 1, we see that IA is the only current flowing into the node. However, there are three paths for current to leave the node, and these current are represented by IB, IC, and ID. Once charge has entered into the node, it has no place to go except to leave (this is known as conservation of charge). The total charge flowing into a node must be the same as the the total charge flowing out of the node.

The two Kirchhoff’s Laws tell us about the relationships between voltages and currents in circuits. Kirchhoff’s Current Law states that: ‘the algebraic sum of currents at a node is zero’. Two points might need further explanation: The second of Kirchhoff’s Laws, the Voltage Law, states that:  ‘the algebraic sum of voltages around a closed circuit loop is zero’. There’s the phrase ‘algebraic sum’ again, so we must recognise that the direction of voltages matters when using Kirchhoff’s Voltage Law.

Practice problems relating to kirchhoff's laws.

Learning to mathematically analyze circuits requires much study and practice. Typically, students practice by working through lots of sample problems and checking their answers against those provided by the textbook or the instructor. While this is good, there is a much better way. You will learn much more by actually building and analyzing real circuits, letting your test equipment provide the änswers" instead of a book or another person. For successful circuit-building exercises, follow these steps:

We saw in the Resistors tutorial that a single equivalent resistance, ( RT ) can be found when two or more resistors are connected together in either series, parallel or combinations of both, and that these circuits obey Ohm's Law. However, sometimes in complex circuits such as bridge or T networks, we can not simply use Ohm's Law alone to find the voltages or currents circulating within the circuit. For these types of calculations we need certain rules which allow us to obtain the circuit equations and for this we can use Kirchoff's Circuit Law.

Example: Three resistors are connected across a 50-volt source. What is the voltage across the third resistor if the voltage drops across the first two resistors are 25 volts and 15 volts? Solution: First, a diagram, such as the one shown in figure 3-23, is drawn. Next, a direction of current is assumed (as shown). Using this current, the polarity markings are placed at each end of each resistor and also on the terminals of the source. Starting at point A, trace around the circuit in the direction of current flow, recording the voltage and polarity of each component. Starting at point A and using the components from the circuit:

Comments

Popular posts from this blog

POWER SYSTEMS LOSS.COM: LOSSES IN ELECTRICAL SYSTEM

What is powersystemsloss all about?    System's loss reduction is now one of the most growing trends in every electric distribution utility. Primarily triggered by economics and regulation concerns, Transmission and Distribution companies now sets more focus in reducing losses and become as an efficient utility as possible in delivering power. Information found in this site will be very useful not only to electrical practitioners but it is also our goal to help students better understand the actual world. Thank you and lets all enjoy learning! continue..   Back to basic    n case you don't know, the power we get from our household electrical outlet didn't just appear in the thin air. It may appear that it is coming out from our walls but we all know that looks can be deceiving. Before reaching our respective homes, electric current passes through miles and miles of c...

FRUITS AS BATTERY AND SOURCE OF ELECTRICITY

Electric Fruits Project   The purpose of this project was to find out which fruit would generate enough electricity to light a light bulb and to discover which fruit would light the bulb the longest. To conduct my experiments I used a Multimeter, copper and zinc wires & electrodes, alligator clips with leads, various light bulbs and five types of fruits. continue.. Why Do Citrus Fruits Produce Electricity?   In order to generate electricity, there must be a power source and a complete circuit. When using a citrus fruit to create electricity, these rules still apply. In a simple experiment using a citrus fruit, the components of the circuit include: a lemon or other fruit, wire, two different metal elements and a small light bulb. The lemon in this circuit serves as the battery and power source. continue.. Fruit Power Project   Purpose To demonstrate how an electrical current can be generated using citrus fruits (such as lemons or li...

ELECTROCUTION: ELECTRIC ACCIDENT THAT CAN BE AVOIDIED

Electrocution   Electrocution is a type of electric shock that, as determined by a stopped heart, can end life. Electrocution is frequently used to refer to any electric shock received but is technically incorrect; the choice of definition varies from dictionary to dictionary. However, in the vernacular, the term electrocution is used to mean: death, murder or a sudden accident caused by an electric shock. deliberate execution by means of an electric shock, such as an electric chair; the word "electrocution" is a portmanteau for "electrical execution".. continue.. Electric Shock   Electric Shock of a (human) body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable. The minimum current a human can feel depends on the current type (AC or DC) and frequency. A person can feel at least 1 mA (rm...