Physical Science 2.02 Honors- Sound Waves Study Guide

🎵 What This Module Actually Covers

Sound waves trip up honors students because they feel invisible. You can't see compression and rarefaction the way you see light. That makes the math and the physics harder to picture.

This study guide breaks down exactly what module 2.02 expects you to know. No filler. No pep talks. Just the concepts, formulas, and problem-solving steps you need to pass the test.

📢 The Basics: What Sound Actually Is

Sound is a mechanical wave. It needs a medium to travel. No air, no water, no steel? No sound. This is why space is silent.

Sound waves are longitudinal. The particles of the medium move parallel to the direction the wave travels. They bunch together in compressions and spread apart in rarefactions.

Mechanical vs. Electromagnetic Waves

🔑 The Four Properties You Must Know

Every sound wave has four measurable traits. Mix them up on the test and you lose points.

• Speed (v): How fast the wave moves through the medium. Depends on temperature, density, and elasticity. Faster in solids than in gases.
• Frequency (f): How many waves pass a point per second. Measured in Hertz (Hz). Determines pitch. Higher frequency = higher pitch.
• Wavelength (λ): Distance between two identical points on the wave, like compression to compression. Shorter wavelength = higher frequency.
• Amplitude: The maximum displacement of particles from rest. Determines loudness. Bigger amplitude = louder sound.

These four are locked together by the wave equation:

v = f × λ

If you know two of those values, you can always find the third. This is the bread and butter of 2.02 math problems.

🧊 How Sound Behaves: Reflection, Refraction, Diffraction, and Interference

Sound waves don't just travel in straight lines and disappear. They bounce, bend, spread, and collide.

Reflection

When sound hits a hard surface, it bounces back. This is an echo. The angle of incidence equals the angle of reflection, same as light. Honors questions often ask you to calculate the time delay between the original sound and the echo using distance and speed.

Refraction

Sound changes speed when it moves from one medium to another, or even between air layers of different temperatures. This bending changes the direction of the wave. That's why sound travels weirdly at night when air near the ground is cooler.

Diffraction

Sound waves spread out after passing through an opening or around an obstacle. Low-frequency sounds (long wavelengths) diffract more than high-frequency sounds. This is why you can hear bass through walls but not the lyrics.

Interference

When two sound waves meet, they combine.

• Constructive interference: Crest meets crest. The amplitudes add up. Sound gets louder.
• Destructive interference: Crest meets trough. The amplitudes cancel out. Sound gets quieter or disappears.

🚗 The Doppler Effect

This one shows up on every honors test. When a sound source moves toward you, the waves in front of it get compressed. You hear a higher frequency (higher pitch). When it moves away, the waves stretch out. You hear a lower frequency (lower pitch).

The actual frequency of the source doesn't change. Your perception changes because the wavelength hitting your ear is different. Police sirens and race cars are the classic examples.

📳 Resonance

Every object has a natural frequency. When an outside force matches that frequency and pumps energy into the system, the amplitude grows huge. This is resonance.

It breaks bridges. It shatters wine glasses. It makes your chest rumble at a concert. Honors questions usually ask you to identify the condition for resonance: the driving frequency must match the natural frequency.

🛠️ How to Solve 2.02 Sound Wave Problems

Don't just stare at the numbers. Follow a system.

1. Draw the scenario. Sketch the source, the medium, and the observer. Label distances and directions.
2. List the givens. Write down every number in the problem with its unit. Convert everything to standard units (meters, seconds, Hertz) before you calculate.
3. Identify what you need to find. Is it speed? Frequency? Wavelength? Time delay for an echo?
4. Pick the right formula. For most problems, v = fλ is your starting point. For echoes, remember the sound travels to the surface and back, so total distance is 2d.
5. Solve and check your units. If your answer comes out in m²/s, you messed up the algebra. Fix it.

Common Traps on Honors Tests

• Forgetting that echo distance is double the one-way distance.
• Confusing amplitude with frequency. Amplitude is loudness, not pitch.
• Assuming sound speed is the same in all materials. It isn't. The problem will give you the speed or expect you to know the standard value for air.
• Mixing up constructive and destructive interference. Remember: same direction = louder, opposite direction = quieter.

🌡️ Temperature and the Speed of Sound

Speed of sound in air changes with temperature. The rough rule:

v ≈ 331 m/s + (0.6 × T) where T is temperature in Celsius.

At 20°C, that's about 343 m/s. At 0°C, it's about 331 m/s. If your problem gives a weird temperature, use this formula. Don't just guess 343.

🔇 Sound Intensity and Decibels

Intensity is power per unit area, measured in watts per square meter. But human hearing spans a massive range, so we use decibels (dB).

The decibel scale is logarithmic. Every 10 dB increase means the intensity multiplies by 10. A 20 dB sound is 100 times more intense than a 0 dB sound, not just 20 times more.

• 0 dB: Threshold of hearing
• 60 dB: Normal conversation
• 120 dB: Threshold of pain

Honors questions often ask you to compare intensities using the logarithmic relationship, not just add decibels together.

🎓 What Honors-Level Questions Look Like

Regular physical science asks you to define terms. Honors makes you apply them.

Expect questions like:

• Calculate the wavelength of a 440 Hz sound wave traveling through air at 25°C.
• A ship sends a sonar pulse to the ocean floor and hears the echo in 4 seconds. How deep is the water?
• Explain why two speakers playing the same note can sound loud in one spot and silent in another.
• A train whistle sounds higher as it approaches and lower as it leaves. Name and explain the effect.

If you can handle those four types, you're ready.