Electronics Revision

Revision cards to help with electronics

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There are 3 types of materials used for electronics.. these include: Electrical Conductors, Electrical Insulator and Semi-Conductor.

Electrical Conductors - allows electricity to flow through them easily; low resistivity values.

Electrical Insulator - prevents electrical flow; have very high resistivity values.

Semi-Conductor - exhibit both conducting and insulating properties.

Most common type of Semi-Conductor is Silicon - there is small amounts of other elements such as Boron and Phosphorous added to it - this causes it to be a Semi-Conductor.

The simplest kind is a Diode.In a diode the electrical current can be made to flow in one direction only If the diode is reversed the flow of current is stopped. This behaviour is due to the semi-conducting property of the doped silicon.

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Electronic components are divided into two groups: discrete electronic components and integrated circuits.

Discrete Electronic - These are separate components that you can combine together to make a circuit on a breadboard, printed circuit board or veroboard.Examples are resistors, transistors, capacitors, relays and LDR's,

integrated circuits - These are miniature circuits etched on to a piece of silicon or chip. These chips are encapsulated inside a protective plastic package, and are also manufactured on a mass scale. The circuits inside the package are arranged in different configurations for particular purposes, but the most common type of configuration is called the dual-in-line(DIL) package, which has two rows of connecting 'legs'.

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Ohms and Resistance Values

The ohm is the unit of resistance. Larger values are measured in kilo-ohms (1000 ohms) and mega-ohms (1,000,000ohms). Resistors are marked, using a code specified in British Standard 1852, as follows:

  • The letter R means ohm. Numbers coming before the R indicate a value more than one. So 1R (or 1R0) = 1 ohm; 47R = 47 ohms; and 4R7 = 4.7 ohms. Numbers coming after the R indicate a value less than one - so R56 = 0.56 ohms.
  • The letter k means kilo-ohm. Numbers coming before the k indicate a value more than one, while numbers coming after the k indicate a value less than one. So 1k8 = 1.8 kilo-ohms and 5k6 = 5.6 kilo-ohms.
  • The letter M means mega-ohm. Numbers coming before the M indicate a value of more than one, while numbers after the M indicate a value less than one. So 2M = 2 mega-ohms, and 2M2 = 2.2 mega-ohms
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The resistance value of a resistor is shown by a series of coloured bands.

  • The first band denotes tens, and the second band units. Each colour stands for a different unit: black is zero, brown is one, red is two; orange is three; yellow is four; green is five; blue is six; violet is seven; grey is eight; white is nine.
  • The third band is the multiplier. Black denotes a multiplier of one; brown 10; red 100; orange 1000 and so on.
  • The fourth band is the tolerance. Manufacturers of resistors cannot guarantee the exact resistance figure shown by the first 3 bands, so they give a percentage value by which the resistance may be higher or lower than the resistance quoted. A red band denotes a tolerance of 2 percent; gold a tolerance of 5 percent; and silver a tolerance of 10 percent.
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splendid work




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