You have a resistor and a capacitor of unknown values. First, you charge the capacitor and discharge it through the resistor. By monitoring the capacitor voltage on an oscilloscope, you see that the voltage decays to half its initial value in 2.5 ms. You then use the resistor and capacitor to make a low-pass filter. What is the crossover frequency fc?
Ch 32: AC Circuits
Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Not the one you use?Change textbook
Chapter 32, Problem 43b
For an RC circuit, find an expression for the angular frequency at which VR = ½ ε0. What is VC at this frequency?
Verified step by step guidance1
Identify the context of the problem: 'VC' likely refers to the voltage across a capacitor in an AC circuit. To solve for VC, we need to understand the circuit configuration and the given frequency.
Recall the formula for the capacitive reactance (Xc), which is given by: , where f is the frequency and C is the capacitance.
Determine the total impedance (Z) of the circuit if it is a series circuit. For a series R-C circuit, the impedance is given by: , where R is the resistance and Xc is the capacitive reactance.
Use Ohm's Law to find the current (I) in the circuit: , where V is the total voltage supplied to the circuit.
Finally, calculate the voltage across the capacitor (VC) using the formula: . Substitute the values of I and Xc to find VC.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Voltage (V)
Voltage, or electric potential difference, is the measure of electric potential energy per unit charge between two points in an electric field. It is expressed in volts (V) and indicates how much work is needed to move a charge from one point to another. Understanding voltage is crucial for analyzing circuits and determining how electrical components interact at a given frequency.
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Capacitance (C)
Capacitance is the ability of a system to store an electric charge, defined as the ratio of the electric charge (Q) stored to the voltage (V) across the system. It is measured in farads (F). In the context of AC circuits, capacitance affects how voltage and current behave at different frequencies, influencing the overall impedance of the circuit.
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Capacitors & Capacitance (Intro)
Frequency (f)
Frequency refers to the number of cycles of a periodic wave that occur in a unit of time, typically measured in hertz (Hz). In electrical circuits, frequency plays a significant role in determining how components like capacitors and inductors respond to alternating current (AC). The relationship between frequency and voltage is essential for understanding the behavior of reactive components in AC circuits.
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Circumference, Period, and Frequency in UCM
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