Prefixes

What is an engineering prefix?
It is also known as SI or metric prefix. It is the name or symbol that comes before a base unit of measurement. Each prefix has a specific value and affects the basic unit by that value. Only one prefix can be used at a time.

How to calculate the value of a prefix measurement?

1. First, determine the prefix and its value.
2. Multiply the measurement by the prefix value and that will be the final value.


• Using 5 kilometers as an example, the prefix is kilo. Using the table below, the value of kilo- is 1000. Thus, 5 kilometers is 5 * 1000 and that equals 5000 meters.


• Another example, consider 89 milligrams. The prefix is milli and milli has a value of .001. 89 milligrams is 89 * .001 which equals 0.089 grams.
  

How to convert from one prefix to another?

1. First, determine the prefix of the original and its value.
2. Then, determine the value of the prefix that you want to convert to.
3. The next step is to take the value of the original prefix and divide by the value of the new prefix.


4. Multiply your original value (don't include the prefix) by the value in step 3. The answer is the new value.


• Ex. Convert 50 kilograms to milligrams. First, the original prefix is kilo and its value is 1000. Second, the value of milli is .001. 1000 divided by .001 equals 1,000,000. The final step is to multiply 50 by 1,000,000 and the result is 50,000,000 mg. So 50 kilograms equal 50,000,000 milligrams.


• Quick shortcut: Once you are familiar with the prefixes, you should recognize them by their powers of tens. Then, conversion from one prefix to another will just involve shifting the decimal point left or right. Shift right when you are going from a higher prefix to a low and shift left when you are going from a lower to a higher one. The amount of times you shift depends on the difference in the powers of tens.
  

Here is a table with some of the most common prefixes used.

• Note that the symbols are case sensitive. The symbols M and m are not the same value.

Resistors Part 1

What is a resistor?
Resistors are one of the most basic electrical components. Resistors are two-terminal devices that are used to limit the flow of current on a electrical circuit. It is measured in ohms. One of the most fundamental equations involving resistors is Ohm's law, V=IR, where R is the resistor's value, I is the current, and V is the voltage across the resistor. Resistors come in various forms and have many possible values.

Determining the value of resistors
Most resistors will have a certain number of colored bands on them. The amount of colored bands usually vary from four to six. Each colored band represents a specific value depending on its location on the resistor.

The resistor color table below shows the values of what each color. This table is specific for a 5-banded resistor. Although, it can be easily used to determine the values of 4 or 6-banded resistors as well.

1. First, count the number of colored bands on the resistor.


• Four bands - First two bands are the first two significant digits of the value.


• Five bands - First three bands are the first three significant digits of the value.


• Six bands - First four bands are the first four significant digits of the value.


• Note that a common problem is determining which side is the start of the resistor. Sometimes, the last band is spaced differently than the other bands.
  





2. Second, determine the significant digits of the resistor based on the colored bands.


• Use the resistor color table to determine the value. Use the # columns and note that each color represents the same value regardless of which band it is.


• Correspond color with value. (Brown is 1, Orange is 3, Blue is 6, etc...)


• Ex. Say the resistor has 4 bands and its first two colors are orange and black. Then, its first two significant digits will be 30.



3. Third, determine the multiplier value.
   
   
   
   • The next band is the multiplier band. (Third band in a 4-banded resistor, fourth band in a 5-banded, and fifth band in a 6-banded one.)
   
   
   • Determine the value of the multiplier from the table. (Yellow is 10,000 and red is 100.)
     
   
   
   • Multiply the multiplier value by the significant digits. The new value will be the value of the resistors.
   
   
   • Ex. Assume a resistor has 5 bands and its first four colors are brown, black, black, and red. Its significant digits will be 100. The multiplier value is 100. Multiply 100 by 100 and the answer will be the value. In this case, the resistor is 10,000 ohms.
     
   
   



4. Finally, determine the tolerance value.
   • Use the table to determine the tolerance value of the color. (Brown is 1% and green is .5%)
   • The tolerance is the limit of variation the resistor is supposed to have.
   • Note that some colors do not have a tolerance value. This can help in figuring out which side is the beginning of the resistor.
     
   • Ex. Assume a resistor has 4 bands and its first four colors are green, black, yellow, and red. Its significant digits will be 50. The multiplier value is 10,000. Multiply 50 by 10,000 and the answer is 500,000. The tolerance is 2%. The value of the resistor will be 500,000 ohms with a 2% tolerance.
     
     

If you are still having trouble with finding the values of a resistor or you just want to check, try using this resistor value calculator.