The AC input and output voltages to the op amp circuit below are:
What is the sum of and ?
Details and Assumptions:
1)
2)
3)
4)
The voltages at the
and
terminals of the op amp are the same
5)
The currents into the
and
terminals of the op amp are zero
6)
The units of
are radians
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From the diagram above, applying Ohm's law gives:
V 1 − V P = I 1 R 1 V 2 − V P = I 2 R 2 V P − V o u t = I R 3
Applying Kirchoff's current law and the current condition for an ideal Op-Amp gives:
I = I 1 + I 2
It is assumed that V G = 0 . Using the ideal Op-Amp voltage condition:
V P = V G = 0
Using all expressions to solve for V o u t gives:
V o u t = − ( R 1 V 1 + R 2 V 2 ) R 3
Given that:
V 1 = − cos ( ω t ) V 2 = sin ( ω t )
Leads to:
V o u t = 3 ( cos ( ω t ) − 2 sin ( ω t ) ) ⟹ V o u t = 2 3 ( 2 cos ( ω t ) − sin ( ω t ) ) ⟹ V o u t = 2 3 5 ( 5 2 cos ( ω t ) − 5 1 sin ( ω t ) ) ⟹ V o u t = 2 3 5 cos ( ω t + arccos ( 5 2 ) )
Which means that:
M = 2 3 5 ; θ = arccos ( 5 2 )
The answer is:
M + θ ≈ 3 . 8 1 7 7 5
Where θ is entered in radians. It would be useful to mention the units of angle to be entered in the problem statement.