PHY098 · Environmental Physics · Classes 9–12
Sound level
Objective: To measure sound levels in decibels and relate them to everyday sounds and hearing safety.
🧰 Apparatus
- Sound level meter (or phone app)
- Sources: quiet room, conversation, traffic, school bell
- Notebook
📐 Formulas and SI units
β = 10 log₁₀(I / I₀) dB, I₀ = 10⁻¹² W/m²
+10 dB = 10 × intensity
💡 Theory
The ear responds to an enormous range of intensities, so we use a logarithmic scale: β = 10 log₁₀(I/I₀) with I₀ = 10⁻¹² W/m². Each 10 dB step is ten times the intensity. Long exposure above 85 dB can damage hearing.
🪜 Procedure
- Measure the background level in a quiet room.
- Measure normal conversation at 1 m.
- Measure traffic at the roadside (from a safe place).
- Measure a school bell from a distance.
- Convert each level to intensity and make a table.
📋 Observations Simulated values
✅ Result and conclusion
An intensity of 10⁻⁵ W/m² is 70 dB, like a busy street.
🔬 In a real lab
Phone apps are not calibrated and meters use A-weighting to match the ear, so readings can differ by a few dB.
⚠️ Safety
Protect your ears above 85 dB; never measure traffic from the road itself.
❓ Quick check
1. +20 dB means the intensity is…
2. 0 dB is…
3. Long exposure risk begins around…
🏋️ Practice
EasyI = 10⁻⁷ W/m². β?
Answer: 50 dB
Mediumβ = 90 dB. I?
Answer: 10⁻³ W/m²
ChallengeTwo identical sources: how many dB louder than one?
Answer: ≈ 3 dB