Final answer:
A black band on a resistor represents the digit 0, serving as a multiplier that effectively adds no zeros to the significant digits of the resistor's value.
Step-by-step explanation:
The digit represented by a black band on a resistor is 0. In the color coding scheme of resistors, the first two colored bands represent significant digits of the resistor's value, the third band serves as a multiplier, and the black color corresponds to the multiplier value of 1, which effectively adds no zeros to the significant digits. Therefore, if the black band is in the third position, it would not change the value of the first two digits, representing the number 0 in terms of multiplication.