Problem 1

Source Problem - 2.3

This circuit is interesting because it is claimed to be an Digital-to-Analog (D-to-A or D/A) Converter.

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Here's the scoop on those voltages.

Each of the input voltages, V_a, V_b and V_c are either zero (0) volts or five (5) volts.
Five volts is interpreted as a digital one (1), and zero volts as a digital zero (0).
The three input voltages represent a binary number that has three bits. That numbe can be anything fro zero (0) to seven (7).
The output voltage is proportional to the input binary number.

Your problem is to answer the following questions.

Which of the voltage sources is the least significant bit (LSB) and which is the most significant bit (MSB)?
Is the output proportional to the digital number represented by the input voltages?
If proportionality exists, what is the constant of proportionality?
It is desired that the output voltage not change by more than 1%. What is the smallest resistor that can be used to load this circuit and not change the output by more than 1%?