Unit D Section 2.0 Technologies can be used to transfer and control electricity

2.1 – Controlling the Flow of Electrical Current Electrical current flows through circuits The amount of current that can flow through a circuit is limited by the conductive properties of the components in the circuit

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Conductors and Insulators In conductors, electrons can move easily because they are not tightly bound to the nuclei of the atoms In insulators, the electrons cannot move easily

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Superconductors A superconductor is a material that have no resistance to electron flow Many materials are superconductive at very low temperatures erconductors

Using Conductors, Resistors & Insulators Resistance is a measure of how difficult it is for electrons to flow Resistance is measured in ohms (Ω) Resistors are parts of a circuit that provide high resistance to reduce the amount of current flowing through the circuit For any given voltage, more current flows through a resistor with a LOW resistance than one through with a HIGH resistance

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Devices that use Resistors The more resistance a substance has, the more the substance gains energy from each electron passing through it. The energy gained is radiated to its surroundings as either heat or light Some examples of devices that use resistors are:

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Switches and Variable Resistors Switches create a break in the circuit that interrupts current flow, therefore controlling the flow of current in the circuit A variable resistor is another type of control These resistors (also known a rheostats) allow you to adjust the amount of current flowing through a circuit, rather than simply turning it on or off This can be done through control knobs or pedals

Topic 2.2 Modeling and Measuring Electricity

Electrical Charge Electrical charge is measured in Coulombs This is named after Charles A. Coulomb 1 coloumb = 6.25 billion billion electrons

2.2 – Modeling and Measuring Electricity Voltage is a measure of how much potential energy each electron that flows through a circuit possesses Voltage is related to both current and resistance in circuits

Ohm’s Law In 1826, Georg Ohm determined through experiments that voltage (V), current (I) and resistance (R) are mathematically related: Resistance is measured in ohms (Ω)

Ohm’s Law states that, as long as temperature remains constant: 1.The resistance of a conductor remains constant 2.The current is directly proportional to the voltage applied

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Applying Ohm’s Law

2.3 – Analyzing and Building Circuits Circuit diagrams or schematics are representations of a circuit that is built Recall that all circuits require four components:

Parallel and Series Circuits Circuits can be divided into two general types: parallel and series These circuit types are defined by the number of branches that are present in the circuit nce/add_aqa/electricity/circuitsact.shtmlhttp:// nce/add_aqa/electricity/circuitsact.shtml

Series Circuits Definition: the current passes through each bulb in turn – there is only one pathway Diagram:

Parallel Circuits Definition: have a separate path for each section of the circuit Diagram

Effects of Multiple Paths in Parallel Circuits In parallel circuits, adding more resistors in circuits actually will reduce the overall resistance of the circuit As well, the voltage change in each branch is equal

Applications of Parallel and Series Circuits Parallel circuits are more commonly used in devices than series circuits Imagine what would occur if your house used series circuits instead of a number of parallel circuits…

Transistors In tiny consumer electronics, transistors are used instead of conventional switches Transistors are made of three layers of silicon sandwiched together These transistors have no moving parts and operate on digital code running through the middle layer of the transistor to control the movement of current through a circuit

Microcircuits Are also called integrated circuits Are made up of microscopic transistors and resistors It is a circuit on an extremely small scale