Additional Science P5 - Current Flow

Revision for B5 Additional Science (Twenty First Century Science course)

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Current Flow

An electric current is usually a flow of free electrons in a piece of metal.

However, some componds will conduct an electric current when they dissolved in water or are melted. These are compounds that form negative and positive ions, which are attracted to positive and negative electrodes placed in the liquid.

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Currents in Circuits - Circuit basics

Circuit diagrams are used to show the wiring of circuits simply, without twisted wires. Some standard symbols are used to represent the circuit components.


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There are 2 measuring instruments shown. Number 4 measures current while number 5 measures the potential difference. Providing the energy to the electrons that flow rounds the circuit is a cell, shown by number 1, a collection of these is known as a battery. A device called a diode allows current to flow one way only (number 3).

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Static Electricity

"Static" means stationary or not moving. The opposite of static is dynamic and these terms can be applied to football teams as well as electricity.

The atom consists of a central nucleus containing protons & neutrons with the electrons orbiting around it. Electrons have a negative charge, the opposite to protons. Rubbing a cloth over a piece of plastic either supplies or removes electrons and leaves it charged. The charge stays there because the plastic is an insulator.

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As more and more static charge builds up the more un-balanced it is. Touching the charged object will cause it to discharge as the charges can now flow away.

The process of charges flowing down to ground is known as earthing. If an object is not "grounded" then the charge can build up causing a large potential difference or voltage. If this becomes very high a spark (collection of charges) may jump from the object to one at a lower potential such as a thunder cloud discharging to Earth.

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Key Words

Electrons - tiny particles of matter that are smaller than an atom and have a negative charge

Ions - electrically charged atoms

Components - parts of the circuits

Potential difference/voltage - the voltage of an electrical current is its forces measured in volts

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