Summary of lesson science electricity 0
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Electricity summary
Scientific ideas, concepts and processes
Electric circuits
Charged particles such as electrons can flow through conductors.
Metals such as copper are good conductors as they contain free electrons.
Power packs and cells (batteries) can supply energy to charges. Batteries convert chemical energy to electrical energy.
Circuit diagrams are used to draw electric circuits. Circuit symbols show wires, lamps, cells, batteries, power packs, buzzers, bells, motors, voltmeters, ammeters, variable resistors and other circuit components.
Lamps can be connected in series and parallel and this affects their brightness, the current and the voltage across each lamp.
Energy sources can be connected in parallel or series and this affects the voltage produced
Electric current
Electrons moving around a circuit are an electric current.
An ammeter is used to measure current
The unit for current is the Ampère, symbol A. (Amp is short for Ampère).
Ammeters are connected in series to measure the current in series circuits and parallel circuits.
The current through circuit components in series is the same at any point. Electric current splits through parallel branches.
Voltage
Electrons carry electrical energy when they move in a circuit.
Energy sources give the electrons energy and energy converters change the electrical energy into radiant energy (lamps), thermal energy (lamps, toasters, heaters), sound energy (TV, radio, stereo) and kinetic energy (motors).
A voltmeter also measures the amount of energy converted when electrons pass through an energy converter.
The unit for voltage is the Volt where 1 Volt = 1 Joule of energy on each Coulomb of electrons.
Power
The electrical power is the amount of energy converted each second
The unit for power is Watts, symbol W.
Power can be calculated using the formula Power = Voltage × Current (P = VI)
Resistance
Conductors and insulators
A conductor is a substance which allows electricity to flow through it.
A substance which is not a conductor is an insulator (or non-conductor).
Metals and graphite conduct electricity because of their free electrons.
Ionic substances conduct if they are molten (liquid) or aqueous (dissolved in water) because the ions are free to move. Molten and aqueous ionic solutions are called electrolytes.
Conductors, like copper wire, have low resistance.
The wires in lamps (Tungsten) and heaters (Nichrome) have higher resistance.
High resistance wires are good energy converters
The resistance of a wire usually increases with temperature.
R is the symbol for resistance and Ohm (Ω) is the unit for resistance
When resistances are connected in series, the total resistance is the found by adding together the individual resistances
Resistance = Voltage ÷ Current (R = V/I) is used to calculate the resistance of an energy converter
The resistance of an energy converter can be found using a variable resistor, power pack, ammeter and voltmeter
An Ohmic Conductor has a resistance which does not depend on the voltage. Current is proportional to voltage and a graph of voltage against current gives a straight line through the origin. The gradient can be used to find the resistance.
A Non-Ohmic Conductor has a resistance which is not constant, and the graph of voltage against current is a curve.
Insulators have a very high resistance.
Light bulbs
A light bulb contains a thin, coiled tungsten filament with a fairly high resistance in a glass bulb of inert gas. It is heated when a current passes through it and glows. Around 5% of the power is emitted as light, with the rest given off as heat.
A fluorescent bulb contains mercury and argon vapour in a glass tube which emits ultraviolet light when a current passes through it. The phosphorescent coating on the inside of the tube produces white light when hit by the ultraviolet light.