# Waves, Sound and Light: Wave Basics

## Wave Basics: Audio Guided Solution

#### Problem 29:

During a classroom demonstration, Mr. H uses a wave machine donated to the school by Bell Telephone Company. The wave machine consists of two 1-meter length sections of 50 steel rods. The steel rods are connected to each other so that when the first rod is disturbed from a rest position, the disturbance travels along the medium from rod to rod. One of the sections consists of longer steel rods; disturbances move at 20 cm/s in this section. The other section consists of shorter steel rods; disturbances move at 80 cm/s in this section. Mr. H connects the two sections together so that pulses can cross the boundary from one section to the other. He introduces a pulse with a length of 10 cm into the slower section. Determine the length of this pulse when it crosses the boundary into the faster section.

## Habits of an Effective Problem Solver

• Read the problem carefully and develop a mental picture of the physical situation. If necessary, sketch a simple diagram of the physical situation to help you visualize it.
• Identify the known and unknown quantities and record in an organized manner, often times they can be recorded on the diagram itself. Equate given values to the symbols used to represent the corresponding quantity (e.g., v = 12.8 m/s, λ = 4.52 m, f = ???).
• Use physics formulas and conceptual reasoning to plot a strategy for solving for the unknown quantity.
• Identify the appropriate formula(s) to use.
• Perform substitutions and algebraic manipulations in order to solve for the unknown quantity.