Elenco Basic Electronic Experiments - Manual (Page 10)

10
MORE ABOUT RESISTORS
Ohm’s Law: You just observed that when you have less resistance in the circuit, more current flows (making the LED
brighter). The relationship between voltage, current, and resistance is known as Ohm’s Law (after George Ohm who
discovered it in 1828):
Voltage
Current =
____________
Resistance
Resistance: Just what is Resistance? Take your hands and rub them together very fast . Your hands should feel warm.
The friction between your hands converts your effort into heat. Resistance is the electrical friction between an electric
current and the material it is flowing through; it is the loss of energy from electrons as they move between atoms of the
material. Resistors are made using carbon and can be constructed with different resistive values, such as the seven parts
included in your PK-101. If a large amount of current is passed through a resistor then it will become warm due to the
electrical friction. Light bulbs use a small piece of a highly resistive material called tungsten. Enough current is passed
through this tungsten to heat it until it glows white hot, producing light. Metal wires have some electrical resistance, but it
is very low (less than 1
Ω per foot) and can be ignored in almost all circuits. Materials such as metals which have low
resistance are called conductors. Materials such as paper, plastic, and air have extremely high values of resistance and
are called insulators.
Resistor Color Code: You are probably wondering what the colored bands on the resistors mean. They are the method
for marking the value of resistance on the part. The first ring represents the first digit of the resistor’s value. The second
ring represents the second digit of the resistor’s value. The third ring tells you the power of ten to multiply by
, (or the number
of zeros to add). The final and fourth ring represents the construction tolerance. Most resistors have a gold band for a 5%
tolerance. This means the value of the resistor is guaranteed to be within 5% of the value marked. The colors below are
used to represent the numbers 0 through 9.
COLOR VALUE
BLACK 0
BROWN 1
RED 2
ORANGE 3
YELLOW 4
GREEN 5
BLUE 6
VIOLET 7
GRAY 8
WHITE 9
Use the color code to check the values of the seven resistors included in your PK-101, and compare to the list below:
YELLOW - VIOLET - BROWN - GOLD is 470
Ω with 5% tolerance
BROWN - BLACK - RED - GOLD is 1,000
Ω (or 1 kΩ) with 5% tolerance
ORANGE - ORANGE - RED - GOLD is 3,300
Ω (or 3.3 kΩ) with 5% tolerance
BROWN - BLACK - ORANGE - GOLD is 10,000 Ω (or 10 kΩ) with 5% tolerance
ORANGE - ORANGE - ORANGE - GOLD is 33,000 Ω (or 33 kΩ) with 5% tolerance
BROWN - BLACK - YELLOW - GOLD is 100,000 Ω (or 100 kΩ) with 5% tolerance
BROWN - BLACK - GREEN - GOLD is 1,000,000
Ω (or 1 MΩ) with 5% tolerance
RED ORANGE
VIOLET GOLD
27 X 10,000 = 27,000
Ω, with
5% Tolerance
Example of Color Code