To determine what happens to the speed of a sound wave when it moves from aluminum to brass, let's consider the provided speeds of sound for both materials:
1. Speed of sound in Aluminum (Al): 6,420 m/s
2. Speed of sound in Brass (70% Cu, 30% Zn): 4,700 m/s
We need to compare these speeds to understand the change in speed of the sound wave as it transitions from aluminum to brass.
- In aluminum, the speed of sound is 6,420 m/s.
- In brass, the speed of sound decreases to 4,700 m/s.
To summarize, when the sound wave moves from aluminum to brass, the speed changes from 6,420 m/s to 4,700 m/s. Since 4,700 m/s is less than 6,420 m/s, the speed of sound decreases.
Therefore, the correct answer is:
D. It decreases.
