The circuit in Fig. 21.18a is called a low-pass filter because a large current and voltage (and thus a lot of power) are delivered to the load resistor (RL) only by a low-frequency source. The circuit in Fig. 21.18b is called a high-pass filter because a large current and voltage (and thus a lot of power) are delivered to the load only by a high-frequency source. Describe conceptually why the circuits have these characteristics.

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Rt R1 ac ac source sourco (al Low-pass filter (b) High-pass filter