Everything Science Grade 12

CHAPTER 14. ELECTRONICS 14.3

C

L next part of circuit...

Figure 14.6: A low passfilter. Low frequencies pass through the inductor and into the
next part of the circuit,while high frequenciespass through the capacitor straight to
ground.

LRC Circuits, Resonance and Signal

Tuning

ESCGE

A circuit containing a resistor, a capacitor and aninductor all in series is called an LRC
circuit. Because the components are in series, the current through each component at
a particular time will bethe same as the currentthrough the others. Thevoltage across
the resistor will be in phase with the current. The voltage across the inductor will be
90 ◦ahead of the current (thecurrent always follows or lags the voltage in an inductor).
The voltage across the capacitor will be 90 ◦behind the current (thecurrent leads the
voltage for a capacitor). The phases of the voltages for the inductorand capacitor
relative to the commoncurrent are shown in Figure 14.7.

Time

I

VL

VC

Figure 14.7: The voltages across the separate components of an LRC circuit. Looking
at the peaks, you see that the voltage across theinductor VL‘peaks’ first, followed 90 ◦
later by the current I, followed 90 ◦later by the voltage across the capacitor VC. The
voltage across the resistor is not shown — it isin phase with the current and peaks at
the same time as the current.