a. Rf/Ri = 100. For example, Ri = 1k and Rf = 100k.
b. Rf/Ri = 99.
c. For the noninverting configuration, the effective input impedance is extremely high and does not load the transducer. There is no change in the gain.
For the inverting configuration, the effective input impedance is the sum of Ri and RTH. If Ri = 10k (and Rf = 1.0M) then the effective gain is 16.7. As Ri decreases, the effective gain approaches 20.
To eliminate loading effects or changes in gain when using an inverting configuration, use a voltage follower between the transducer and the inverting stage.