# Current

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Physics

Electric current is denoted by the variable I and is defined as the flow of positive charges. However, the flow of electrons, which are negatively charged, actually creates the current. Electric current is defined mathematically as charge over time, with charge measured in Coulombs and time measured in seconds. The units of electric current are Coulombs per second, known as an ampere or amp.

Electric current is driven by a voltage or potential difference. A circuit is a closed loop path of conducting wire that typically contains a voltage source and common circuit elements. The behavior of electric currents and voltages in circuits are governed by two primary rules known as Kirchhoff's laws. Kirchhoff's junction rule states that the sum of all currents coming into a junction must be equal to the sum of all currents leaving the junction, while Kirchhoff's loop rule states that the sum of voltage rises from voltage sources (or EMFs) must equal the sum of voltage drops across circuit elements.

Lesson Outline

<ul> <li>Introduction to electric current <ul> <li>Directed motion of a large number of charges</li> <li>Denoted by the variable capital I</li> </ul> </li> <li>Defining electric current <ul> <li>Flow of positive charges</li> <li>Typically created by flow of electrons, which are negatively charged</li> <li>Charge over time: units are Coulombs per second, also known as ampere or amp (A)</li> </ul> </li> <li>Cause of electric current: potential difference (voltage) <ul> <li>Two types: direct current (DC) and alternating current (AC)</li> <li>Focus on direct current for this lesson</li> </ul> </li> <li>Electromotive force (EMF) <ul> <li>Source of potential difference, like a generator or battery</li> <li>Not actually a force, but the potential difference provides the "push" needed for charges to flow</li> </ul> </li> <li>Circuits <ul> <li>Closed loop path of conducting wire containing voltage sources and circuit elements</li> <li>Governed by Kirchhoff's laws</li> </ul> </li> <li>Kirchhoff's junction rule <ul> <li>Sum of currents entering a junction must equal the sum of currents leaving the junction</li> <li>Essentially a restatement of conservation of charge</li> </ul> </li> <li>Kirchhoff's loop rule <ul> <li>Sum of voltage rises must equal the sum of voltage drops across circuit elements in a closed loop</li> </ul> </li> </ul> Don't stop here!

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FAQs

###### What is the difference between direct current (DC) and alternating current (AC)?

Direct current (DC) is the uni-directional flow of electric charge, maintaining a constant polarity. In contrast, alternating current (AC) flows in different directions, periodically reversing its direction. DC is commonly produced by batteries, solar panels, and fuel cells, while AC is used in our homes, generated and distributed by power stations.

###### What is the role of a voltage source and EMF in a circuit?

A voltage source provides the potential difference (voltage) required to maintain the flow of electric current in a circuit. Electromotive force (EMF) is the energy provided by the voltage source that causes the movement of electrons, driving the current. EMF can be thought of as the work done per unit charge to move the charges through the circuit, and it's often provided by devices like batteries, generators, or solar panels.

###### How do Kirchhoff's junction rule and loop rule help in analyzing circuits?

Kirchhoff's junction rule is based on the principle of conservation of electric charge, stating that the total current entering a junction in a circuit must equal the total current leaving the junction. Kirchhoff's loop rule is based on the principle of conservation of energy, stating that the sum of the potential differences (voltages) in any closed loop within a circuit must equal zero. These rules are crucial for understanding and analyzing complex electrical circuits.

###### How is electric current measured and what are amperes?

Electric current is measured in amperes (A), which is a unit of the International System (SI). An ampere represents the flow of one Coulomb of charge passing through a point in a circuit every second. It serves as the basic unit to quantify the rate of flow of electrical charges and to evaluate the performance of electrical components in a circuit.