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## Creating Pressure waves in a Coax Cable: Instructor's Guide

### Main Ideas

• Non-dispersive wave propagation
• Relationship between voltage and current
• Understanding how a wave propagates inside a coaxial cable
• How voltage is measured in a coaxial cable
• Material velocity v. propagation speed

Estimated Time:15 minutes

• Students formed two equally spaced lines on the opposite sides of the classroom and moved as if they were electrons inside a coaxial cable when the instructor sent a “voltage” wave down the cable.

### Prerequisite Knowledge

• Basic understanding of how waves propagate in the air

### Props/Equipment

• More than 10 students

### Activity: Introduction

In a brief mini-lecture, students are introduced to the idea that as electrons move back and forth locally, a potential difference is created between the inner part and outer part of a coaxial cable.

### Activity: Student Conversations

• How voltage is measured – Some students don't realize that the inner part and the outer part of the coaxial cable do not affect each other. It is the relative motion between the movement of the electrons from both sides that creates the potential difference across the coaxial cable.
• Material velocity v. Propagation speed – Emphasize that an electron does not travel from one end of the cable to the other end of the cable. Instead, the vibration of each electron was the way the wave propagated inside the coax cable. The analogy of how sound wave propagates in the air would be favorable in this case.

### Activity: Wrap-up

No specific wrap-up is needed.

### Extensions

The Pressure Wave Simulation is an good follow-up to this activity.

Together, these two activities provide an excellent set up for the Wave Propagation in a Coaxial Cable lab.

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