14.3 CHAPTER 14. ELECTRONICS
the flow of DC and lowfrequency AC because its reactance increases with decreasing
frequency.
When the frequency ishigh, the capacitive reactance is low. This is why a capacitor
allows the flow of highfrequency AC because its reactance decreases with increasing
frequency.
Therefore putting a capacitor in a circuit blocks the low frequencies and allows the
high frequencies to pass. This is called a high pass filter. A filter like this can be used
in the ‘treble’ setting ofa sound mixer or musicplayer which controls the amount of
high frequency signal reaching the speaker. Themore high frequency signal there is,
the ‘tinnier’ the sound.A simple high pass filtercircuit is shown in Figure 14.5.
C next part of circuit...L
Figure 14.5: A high pass filter. High frequencies easily pass through thecapacitor and
into the next part of the circuit, while low frequencies pass through the inductor straight
to ground.
Similarly, if we examinethe equation for the reactance of an inductor, we see that in-
ductive reactance increases with increasing frequency. Therefore, when the frequency
is low, the inductive reactance is very low. Thisis why an inductor allows the flow of
DC and low frequency AC because its reactancedecreases with decreasing frequency.
When the frequency ishigh, the inductive reactance is high. This is why an inductor
blocks the flow of highfrequency AC because its reactance increases with increasing
frequency.
Therefore putting an inductor in a circuit blocksthe high frequencies and allows the
low frequencies to pass. This is called a low pass filter. A filter like this can be used
in the ‘bass’ setting of asound mixer or music player which controls the amount of
low frequency signal reaching the speaker. The more low frequency signal there is, the
more the sound ‘booms’. A simple low pass filter circuit is shown in Figure 14.6.