The characteristic of a vibration that determines its intensity is the

1. Analyze the question The question asks which property of a vibration (wave) decides its intensity. For sound, intensity relates to loudness.

2. Explain the concept Intensity is the energy passing per unit area per second (power per unit area). For a vibrating source:

• Energy of vibration is proportional to the square of the amplitude
• So, Intensity ∝ (Amplitude)² (I ∝ A²)

The other options describe different things:

• Frequency determines the pitch of a sound.
• Overtone (with harmonics) determines the quality or timbre of a note.
• Wavelength is linked to frequency through v = fλ. It describes the length of one cycle, not the energy carried.
• Amplitude is the maximum displacement from the rest position. It determines the energy carried, and so the intensity or loudness.

3. Solution

• Bigger amplitude → more energy → greater intensity (louder sound, brighter light).
• Smaller amplitude → less energy → lower intensity.

If the amplitude doubles, the intensity becomes 2² = 4 times as large.

4. Answer The characteristic that determines intensity is the amplitude, which is option D.

5. Exam tip Memorize these pairs:

• Pitch → Frequency
• Loudness/Intensity → Amplitude
• Quality/Timbre → Overtones (waveform)

JAMB repeats this trio often, so it is an easy mark to secure.