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Glossary of terms you will come across during your Phase 2 training.

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When the anode of a diode is connected to a positive supply, and the cathode to a negative supply, the diode is said to be forward-biased. The diode will tend to conduct in this condition.

For the diode to actually conduct in this condition, (forward biased), the voltage must reach a certain minimum level before any current flows. This value for a diode is known as its 'forward voltage'.

When these connections are reversed, and the anode is connected to the negative supply and cathode is connected to the positive supply, the diode is said to be reverse-biased. The diode will not conduct in this condition.

It should be noted that when a diode is reverse-biased, there is always a certain amount of 'leakage'. In addition, if the reverse voltage is high enough, the diode will break down and will conduct in the reverse direction (for example, a zener diode). Other ordinary diodes can be destroyed by being subjected to excessive reverse voltage.

In the context of LEDs, each of them has a value called 'forward voltage'.
This is the voltage that must be put on the anode of the diode in order for current to begin to flow through the diode.

Represented in datasheets with the abbreviation Iq, quiescent current is the current used by a device when it is ready to operate, but not yet supplying any current to a load.

You can think of quiescent current as the current required have a device ready to perform a task, but not yet performing that task.

You could also think of it as the current used by a component when it is powered up, but not yet operating.


Acceleration is simply a change in speed.

Acceleration can be positive - an object speeds up, or it can be negative - an object slows down.

The kind of acceleration we all experience every day is the acceleration produced by gravity - 9.81m/s2, referred to as 'g' in engineering calculations.

For example, in order to calculate the weight of an object, we multiply its mass by the acceleration produced by gravity:


  • The weight of an object is measured in newtons, N, which is a base derived SI unit.
  • The mass of an object is measured in kilogrammes, kg, which is a base SI unit.
  • The acceleration produced by gravity is measured in metres per second, m/s, which is a base derived SI unit.

Gustav Kirchoff, image from WikipediaGustav Kirchoff, a German physicist, responsible for two electrical laws:

  • Kirchhoff's current law
    Current going into a circuit is always equal to the current coming out of a circuit - in other words, any electricity that goes into a circuit, must come back out of that circuit. 
  • Kirchhoff's voltage law
    In an electrical circuit, the total sum of the individual voltage drops is always equal to the supply voltage.
    For example, if you have a voltage of, say, 12V on a circuit with a single electrical load, and you measure the voltage drop across the load at 11V, this means that you are dropping 1V elsewhere in the circuit and you have a problem.
    Voltage drop in a circuit is unavoidable, so we have acceptable limits.
    For the live part of a circuit, the limit is approximately 0.25V (up to 0.5V in starter motor circuits).
    For the earth part of the circuit, the voltage drop should be 0V, or very close to it.

You can read more about Gustav Kirchhoff on Wikipedia

You can read more about Kirchhoff's circuit laws on Wikipedia


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