Characteristics and Applications | Class 9 Science Notes
By ConceptScroll Team · Published on 17 July 2026 · 2 min read
Characteristics and Applications – this guide gives you a concise, exam-ready overview of Characteristics and Applications from Class 9 Science, written by ConceptScroll editors and reviewed against the latest NCERT textbook.
10.6 Characteristics of a Sound Wave
Sound waves are characterized by wavelength, frequency, time period, amplitude, intensity, and speed. Wavelength (λ) is the distance between two consecutive compressions or rarefactions. Frequency (ν) is how often density oscillations occur per second, measured in hertz (Hz). Time period (T) is the time for one complete oscillation, with ν = 1/T. Amplitude is the maximum change in air density and relates to the energy carried by the wave; larger amplitude means louder sound. Intensity is the energy passing through a unit area per unit time and decreases with distance from the source as energy spreads over a larger area. The speed of sound (v) is the distance a wave crest travels per unit time, given by v = λ × ν. Sound travels fastest in solids, slower in liquids, and slowest in gases. Temperature and humidity affect the speed of sound in air. Human perception of sound includes pitch (related to frequency) and loudness (related to amplitude). The audible range for humans is approximately 20 Hz to 20,000 Hz. Sounds below 20 Hz are infrasonic; above 20 kHz are ultrasonic. Loudness is measured in decibels (dB), and excessive loudness can cause hearing loss. The section includes examples calculating frequency, wavelength, speed, and distance using sound properties.
📊 Diagram: Fig. 10.18: Sound waves with different wavelengths; Fig. 10.19: Graphical representation of a sound wave; Table 10.1: Speed of sound in different media at 15°C
🧪 Activity: Activity 10.8: Using sound-generating apps to listen to sounds of different frequencies and observe changes in pitch and loudness.
🔗 Connection: These characteristics help understand human perception of sound and lead to studying reflection phenomena like echo and reverberation.
Frequently asked questions
What is a semiconductor and how does its electrical conductivity compare to conductors and insulators?
A semiconductor is a material whose electrical conductivity lies between that of conductors and insulators. For example, silicon and germanium are semiconductors that conduct electricity better than insulators but not as well as conductors.
How does the electrical conductivity of semiconductors change with temperature, and how is this different from conductors?
In semiconductors, electrical conductivity increases with temperature because more electrons gain energy to jump from the valence band to the conduction band. In contrast, in conductors, conductivity decreases with temperature due to increased lattice vibrations that scatter electrons.
Which of the following materials is a typical semiconductor?
Silicon
What is doping in semiconductors and how does it affect their electrical conductivity?
Doping is the intentional addition of impurities to a pure semiconductor to increase its electrical conductivity. For example, adding phosphorus (five valence electrons) creates an n-type semiconductor with extra electrons, while adding boron (three valence electrons) creates a p-type semiconductor with holes.
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