Figure 5: Scaling the Magnitude of a Signal
Consider the circuit shown in Figure 5.
Figure 5: Scaling the Magnitude of a Signal
Because no current flows into the op-amp and because all current at
a node must sum to zero, the current entering the input leg must be equal
to that flowing throught the feedback leg from the input to the output
( 
).
We also know that the voltage at the inverting input must be zero
(that is the voltage indicated by the ground shown connected to the
non-inverting input).
From our properties of resistors, then, we know that
Consequently,
which means that we're multiplying the magnitude of the input voltage
by the constant 
.
Notice that the sign of the voltage has changed. This is a universal trait of the type of op-amp circuits we'll be using in analog computers. As we'll see in the example, it doesn't cause any significant problems in using the computer.