Question

A carbon resistance reads Red-Red-Black. What is its resistance?

Answer 1

In order to find the resistance of the carbon resistor the application of the respective color codes for each of the different colors is required. The method to find the color code and hence the correct resistance value is interpreted from the three lines present on the resistor.

Complete answer:
Carbon resistors are used for many purposes in electrical circuits so that they can have resistance values varying from a few ohms to a million ohms and due to its wide range of resistance it is used in devices like radio receivers, amplifiers etc.
A carbon resistor is made up of a mixture of clay, carbon and resin binder pressed together to be molded into rod-like shapes which are enclosed by an outer covering or a plastic layer.
These resistors typically consist of three lines drawn on them which signify certain rules in order to find the resistance value indicated by the colors of the stripes on the carbon resistor. There is a fourth line as well which indicates the tolerance which may or may not be used when calculating the resistance value.
The color codes for these carbon resistors are used to signify the resistance value of the carbon resistor and its accuracy in terms of percentage. There are ten colors which are each assigned with digits or values representing them and will each also have a multiplier value as well which is already assigned to it. So thus, based on the color strips present on the carbon resistor the resistance value needs to be determined.
The first band or strip specifies the first significant figure for the resistance value while the second band, that is, the value of the color of the second band represents the second significant figure. The third band indicates the multiplier value which is in terms of a power of ten to which the two significant figures obtained from the two colored strips are multiplied to.
In the question, there are three colors, that is, red, red and black are given. Thus, as per the values assigned to the color red the value is two. This is in accordance with the color code table containing the color code values assigned to each color. Since it is mentioned that the first as well as the second band is red the first of significant figures are 2 and 2 respectively. The color value given as the third band is black and its corresponding multiplier value in accordance with the color code table is ${10^0}$.
Hence, the total value as mentioned above is: $22 \times {10^0}\Omega$ $= 22\Omega$

Note:
The tolerance which is indicated by the fourth band is mentioned in the carbon resistor in order to specify the percentage accuracy and how the estimated value may vary or deviate as there is a chance of the values varying by a slight amount from its original value.