Question 7.2: Calculate the phase shift for an RC lag network for each of ...
Calculate the phase shift for an RC lag network for each of the following frequencies, and then plot the curve of phase shift versus frequency. Assume f_c=100 Hz.
(a) f = 1 Hz (b) f = 10 Hz (c) f = 100 Hz (d) f = 1000 Hz (e) f = 10 kHz
(a) \phi=-\tan ^{-1}\left(\frac{f}{f_c}\right)=-\tan ^{-1}\left(\frac{1 \mathrm{~Hz}}{100 \mathrm{~Hz}}\right)=-\mathbf{0 . 6}{ }^{\circ}
(b) \phi=-\tan ^{-1}\left(\frac{10 \mathrm{~Hz}}{100 \mathrm{~Hz}}\right)=-\mathbf{5 . 7 ^ { \circ }}
(c) \phi=-\tan ^{-1}\left(\frac{100 \mathrm{~Hz}}{100 \mathrm{~Hz}}\right)=-\mathbf{4 5 . 0 ^ { \circ }}
(d) \phi=-\tan ^{-1}\left(\frac{1000 \mathrm{~Hz}}{100 \mathrm{~Hz}}\right)=-\mathbf{8 4 . 3 ^ { \circ }}
(e) \phi=-\tan ^{-1}\left(\frac{10 ~\mathrm{kHz}}{100 \mathrm{~Hz}}\right)=-\mathbf{8 9 . 4 ^ { \circ }}
The phase shift versus frequency curve is plotted in Figure 7–6 . Note that the frequency axis is logarithmic.
P R A C T I C E EXERCISE
At what frequency, in this example, is the phase shift -60°?
