Operational Amplifiers

Step 1: Understanding the circuit.
In the given circuit, the Zener diode is used to maintain a constant voltage of 4.7 V, and the OPAMP works as a voltage follower. The input voltage , and the output voltage is regulated to 9 V.
Step 2: Calculate the value of resistance .
Using the voltage divider formula, the output voltage can be written as: where is the resistance of the Zener diode. We are given and .
Step 3: Solve for .
Substitute the known values: Solving this equation gives , so the value of is between 1.05 and 1.15 kΩ.