Electrical Theory Glossary

Basic Electrical Concepts

Basic Electrical Circuits

 

Basic Electrical Concepts

  • Matter may be defined as anything which occupies space.
  • Matter exists in either of three forms: solid, liquid, and gas.
  • A substance is a definite kind of matter, all specimens of which have the same physical and chemical properties.
  • An element is a substance which cannot be separated into simpler substances by chemical means.
  • Compound substances are made up by chemical combination of definite proportions of 2 or more elements
  • A mixture is composed of two or more substances which do not enter into chemical union, and in which the separate natures of the mixed substances may be determined by other than chemical means.
  • An atom is the smallest part of an element which can enter into a chemical change
  • A molecule is the smallest particle of a substance which can exist and still have all the properties and characteristics of the substance.
  • In a solid, the molecules firmly adhere together and strongly resist being separated.
  • In a liquid, the molecules are separated and the liquid takes up the shape of the containing structure.
  • The molecules of a gas are in a constantly turbulent condition, colliding with each other, and striking against the barriers of any containing structure, thus causing the dispersal throughout the available space.
  • Temperature, and to a lesser extent pressure, largely determine the state of a substance.
  • The usual effects of increasing the temperature of a substance are to increase the rate of vibration of the molecules and to expand the substance.
  • The electron theory states that all matter is composed of positive and negative electric charges. Matter is electricity.
  • An electron is a negatively charged particle of an atom. It can sometimes be separated from its atom and as such is called a “free electron”.
  • A proton is a positively charged particle of an atom. A proton can’t readily be separated from its atom. The mass of a proton is 1,836 times that of an electron.
  • A neutron is an elementary particle the mass of which is roughly equal to that of a proton but having no resultant charge. It is thought to be made up of one electron closely grouped with a proton.
  • So Long as the balance between the number of electrons and protons is unaltered, an atom is electrically neutral.
  • The centre of the atom is called the nucleus, and spinning around this nucleus at almost incredible speed are the planetary electrons.
  • An ion is an atom carrying an electric charge.
  • Electric current is a flow of electrons.
  • Static electricity takes the form of electric charges on the surface of bodies.
  • A negative charge exists on a body which has an excess of electrons.
  • A positive charge exists on a body that has a deficiency of electrons.
  • Law of electrostatic attraction is that like charges repel each other, unlike charges attract each other.
  • Friction charging is when friction occurs between 2 unlike substances, electrostatic charges are set up due to the rearrangement of the surface electrons and accumulate on one, or both of the substances.
  • The coulomb is the quantity of electricity conveyed by a current of one ampere in one second. For example: 1 coulomb = 1 ampere / per second.
  • Quantity of electricity Q=I t coulombs, where I = current in amperes, and t = time in seconds.
  • The quantity of electricity measured in terms of ampere-hours is equal to the product of the mean current in amperes, and the time in hours during which it flows. (one ampere-hour is equal to 3600 coulombs).

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Basic Electrical Circuits

Electrical terms used in electrical circuits are:

  • Voltage- potential difference – symbol V
  • Current – electrical flow – symbol I
  • Resistance – opposition to flow – symbol R

The basic electric circuit is made up of the following five parts:

  • A source of electrical pressure such as a battery to provide electrical energy
  • A complete path to allow flow to take place such as wires and conductors
  • A load such as a device in the circuit that expends energy like a laptop or motor
  • A device to control the current flow (to control the circuit operations) such as a switch to allow an on and off state.
  • A device to protect the circuit such as fuses or circuit breakers

When an electrical pressure, known as voltage, is applied to a closed circuit a path is completed allowing electrical current to flow. Electric current is a flow of electrons which occurs when there is potential difference (pressure difference) across a circuit. i.e. flow from a high potential to a lower potential. To protect the load and the source from too much energy, protection devices such as fuses and circuit breakers are commonly used to provide the weakest link in the circuit. These components automatically disconnect the supply if too much current flows in the circuit (causing fuses to melt). These protective components are placed in series with the electrical load. Rewireable fuses are a low cost device but have a relatively slow response and the fuse element can be replaced with a larger size. High rupturing capacity (HRC) fuses have a high speed response, can handle high energy levels but have a higher cost for replacement cartridges than the rewireable type. Circuit breakers have the advantage that they can be reset after tripping, rather than requiring a replacement element. Electrical schematic diagrams are used to represent an electrical circuit, these circuit diagrams use symbols rather than pictorial representation of the circuit components for simplicity and ease of drawing. Open Circuit: That is an open circuit that prevents current flow Closed Circuit: A Closed Circuit that allows current to flow freely To measure the electrical pressure between 2 points in a circuit, a voltmeter is used. The voltmeter is connected in parallel with the device or supply where the electrical pressure is required to be measured. To measure the electrical current flow in a circuit the ammeter is used. The ammeter is connected in series with the load. top