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## LRC Circuit: Impulse Driver: Instructor's Guide

### Main Ideas

• LRC circuit.
• Impulse driving voltage.

Estimated Time:20 minutes

The students are to observe the current response (as measured by voltage across the resistor) of the series LRC circuit to an impulse driving voltage. This is the same circuit that they previously investigated with sinusoidal driving voltages.

### Prerequisite Knowledge

Knowledge of the response of the series LRC circuit to a sinusoidal driving voltage. Facility with oscilloscope and function generator.

### Props/Equipment

• Tabletop Whiteboard with markers
• The series LRC circuit that the students used previously, function generator with pulse generator adaptor.

### Activity: Introduction

Students are asked to predict the response (current, as measured by voltage across the resistor) of the circuit before they do the measurement, by drawing the expected waveform on a whiteboard.

### Activity: Student Conversations

Some students predict an impulse response from the circuit, others correctly reason that this is a “kick” and that the response will be the ring-down response of a damped oscillator. Other students bring ideas from DC circuits and predict exponential decay or build up.

### Activity: Wrap-up

Wrap-up discussion involves resolving the issues raised in the student conversations, and reinforcing that the ringing response is indeed expected, and posing the question of how it is related to the discussion of simultaneous application of sinusoidal drivers of the same size at all possible frequencies. Namely, one expects a superposition of all possible sinusoidal currents with appropriate magnitudes and phase shifts, and the Fourier transform of that response should be the impedenace measured (frequency)point-by-(frequency)point in the previous lab.

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