The 220 kΩ feedback resistor in the circuit in Figure.1 is replaced by a variable resistor...

The 220 kΩ feedback resistor in the circuit in Figure.1 is replaced by a variable resistor Rf . The voltages υa –υd have the same values as given in Problem (a).

a) What value of Rf will cause the op amp to saturate? Note that 0 ≤ Rf ≤ ∞.

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b) When Rf has the value found in (a), what is the current (in microamperes) into the output terminal of the op amp?

Problem (a).a) The op amp in Figure. 1 is ideal. Find υo if υa = 4 V, υb = 9 V, υc = 13 V, and υd = 8 V.

Figure. 1