2C2  Understand that two or three resistors can be arranged to act as a potential divider and apply the formula.
The formula for resistors in a potential divider will be provided.
The prefixes milli and kilo may be involved for some of these calculations.

Potential Dividers

Understand that two or more resistors can be arranged to act as a potential divider and apply the formula

The formula is :- Potential Divider

When a connection is taken from the junction between two resistors in series this is know as as fixed potentiometer or potential divider.

Note that R1 is nearest to the Positive + rail and R2 is nearest to the Negative - rail.

With the two resistors in this configuration a voltage somewhere between the maximum and minimum would be measured at the point marked "out" depending upon the values of the resistors. This fixed combination is usually replaced by a single resistor in which the output can be changed by moving a slider along the track.

The output could be taken from anywhere along the resistor.

Without necessarily knowing it, you have all used such a potentiometer on the audio gain control on your transceiver / receiver !!!

Potential Divider formula

However a potential divider can be two or more resistors but what ever number it is the resultant formula would be

as we would have to do separate calculation to end up with two resistors.

Looking at the diagram,

you can see that the output is leaving the potential divider of R1, Ra and Rb at the link between R1 and Ra.

With Ra and Rb are in series we can simply add together their values and come up with R2. This R2 we can use in the formula ................. simple eh ??

The V_out is thus dependent upon :-

• V_in


• R1


• R2

Example if Volts in are 12V  R1 = 10 ohms and R2 = 30 ohms then

Vout= 12 x 30/(10 + 30)

Vout = 12 x 0.75

Vout = 9V

Understand the prefixes pico, nano, micro, milli, kilo, Mega and Giga.

In the FLC you learned about milli kilo and Mega - m,k,M so there are four new ones to learn.

Some students find it difficult to convert down the scale from larger to smaller numbers when it is less than 1  -- perhaps the following will help.

Try to see the pattern in the numbers and write out how to convert from one to another in the way you can understand.

Try with the example below. To start with always relate the number to 1

Example

Convert 0.001 micro to nano farads ?

1 micro farad = 0.000001

Thus relative to 1 farad 0.001 micro farads = 0.00000001

we have added the extra 3 zeros  one for the decimal point and the other two from the 001

We now have 8 zeros

from above we know that

relative to 1 farad that 1 nano farad = 0.000000001

that is 8 zeros so 0.001 micro farads = 1 nano farads.

A student (from an early course who has now progress to an Advanced licence) suggested the following to help you remember the order down from the biggest to the smallest,

Goal Makers Kick Once Many Underestimate Noise Pollution

Goal = Giga

Makers = Mega

Kick = kilo

Once = 1

Many = milli

Underestimate = u for micro

Noise = nano

Pollution = pico

At Intermediate level you need to recall the Engineering Notation for key units and sub-units and be able to change between them, but there will be no calculations requiring you to use the notation.

The three zero steps in the units and sub-units translate into changes of x 10³ with each level of unit or sub-unit:

Giga = x 10⁹

Mega = x 10⁶

Kilo = x 10³

Milli = x 10^-3

Micro = x 10^-6

Nana = x 10^-9

Pico = x 10^-12

However at Intermediate level you need to recall the Engineering Notation for key units and sub-units and be able to change between them.

Units of measurement and multiple/sub-multiple prefixes.

The ILC will be taking you much much deeper into electronic theory than the FLC and the course will assume that you have a good working knowledge of all of the FLC technical basics. Some revisions will be given but mainly the ILC will be new information that needs to be fully understood stage by stage before passing onto the next part. So don't rush your learning and remember to chat to your course tutor about anything that is not clear. Even if you think that you are asking a silly question "ASK IT" !!

In this part of the syllabus is going over five items that you learned (or should have learned) in the FLC and only introducing two new items.

However it has come to our notice that some students do not know the units of resistance, inductance, capacitance etc. These unit must be learned so that they are second nature to you so that in a question such as :-

The value of a capacitor is given in ? You readily know to tick the box next to Farads.

Quantity	Symbol	Units	Comment
Potential Difference	V	Volts (V)	Learned in FLC
Current	I	Amps (A)	Learned in FLC
Resistance	R	Ohms	Learned in FLC
Power	P	Watts (W)	Learned in FLC
Frequency	f	Hertz (Hz)	Learned in FLC
Capacitance	C	Farad (F)	New for ILC
Inductance	L	Henry (H)	New for ILC

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