Components and Laboratory Practice
Resistors and Capacitors
Resistors used in the laboratory are usually made of carbon or metal films. Their
resistance values are labeled by using color bands. Black, brown, red, orange, yellow,
green, blue, purple, gray, white represent numerical values, 0-9. The first and second
color stripes represent the first and second significant digits. Except for high precision
resistors, the third color stripe represents the multiplication factor. For example, brown
green red represents 15
, i.e., 1.5 k
. The fourth color stripe, if present, represents
the tolerance. For example, gold represents 5% tolerance.
Carbon film resistors come with standard values. The values are chosen so that
they cover the entire range when the tolerance is taken into account. Standard values are
10, 15, 22, 33, 47, and 68. Only high-precision, metal-film resistors offer a great variety
of values. Students should be aware that it is not necessary to build circuits using the
exact resistance according to the circuit design and results of simulations. For example, if
the circuit design indicates that a 1.56 k
resistor is needed, you may simply use a
standard resistor close to the desired value, e.g., 1.5 k
. It is a good idea to keep a
collection of resistors: 1/4-W, 10
through 1.5 M
. You will also need a 1-W, 100
resistor for the dc power supply experiment.
In addition to resistance, one shall also pay attention to the power rating of a
resistor. The power dissipated by a resistor is given by V
/R, where V is the voltage
applied to the resistor; or I
R, where I is the current flowing through the resistor.
Operating above the power rating can overheat and will burn the resistor eventually.
Potentiometers are also useful. They can be used as variable resistors. However, because
of cost, they are rarely used in manufacturing except for adjustments to be performed in
the field. They are convenient for fine tuning. A potentiometer has three pins. The middle
pin connects to the wiper, which can move from one end to the other.
potentiometer is placed on the prototype circuit board, the pins are hidden underneath