12. Sound

Description:

Struggling with the concepts of Sound in Class 9 Science?

This PDF is your shortcut to scoring higher with well-curated important questions, created by expert teachers in line with the current CBSE pattern.

Perfect for class tests, term exams, and board prep, this e-book covers 1-mark, 2/3-mark, and 5-mark questions, including conceptual, reasoning, and application-based formats.

What’s Inside This PDF?

✅ 1 Mark Questions – Definitions, formulas, fill-ups, MCQs

✅ 2 & 3 Mark Questions – Conceptual questions with reasoning

✅ 5 Mark Questions – Long answers with real-world applications

✅ Fully covers: Nature of sound, wave properties, echo, reflection, applications of ultrasound, and more

What You Will Learn?

✅ Sound is produced due to vibration of different objects. 

✅Sound travels as a longitudinal wave through a material medium. 

✅ Sound travels as successive compressions and rarefactions in the medium. 

✅ In sound propagation, it is the energy of the sound that travels and not the particles of the medium. 

✅ The change in density from one maximum value to the minimum value and again to the maximum value makes one complete oscillation. 

✅ The distance between two consecutive compressions or two consecutive rarefactions is called the wavelength, λ. 

✅ The time taken by the wave for one complete oscillation of the density or pressure of the medium is called the time period, T. 

✅ The number of complete oscillations per unit time is called the frequency (ν), 1 v = . T 

✅ The speed v, frequency ν, and wavelength λ, of sound are related by the equation, v = λν. 

✅ The speed of sound depends primarily on the nature and the temperature of the transmitting medium. 

✅ The law of reflection of sound states that the directions in which the sound is incident and reflected make equal angles with the normal to the reflecting surface at the point of incidence and the three lie in the same plane. 

✅ For hearing a distinct sound, the time interval between the original sound and the reflected one must be at least 0.1 s. 

✅ The persistence of sound in an auditorium is the result of repeated reflections of sound and is called reverberation.

✅ Sound properties such as pitch, loudness and quality are determined by the corresponding wave properties.
Loudness is a physiological response of the ear to the intensity of sound. 

✅ The amount of sound energy passing each second through unit area is called the intensity of sound. 

✅ The audible range of hearing for average human beings is in the frequency range of 20 Hz – 20 kHz. 

✅ Sound waves with frequencies below the audible range are termed “infrasonic” and those above the audible range are termed “ultrasonic”. 

✅ Ultrasound has many medical and industrial applications

Why Choose This Question Bank?

✅ Based on frequently asked CBSE questions

✅ Helps with concept clarity + score boost

✅ Suitable for both daily practice and last-minute revision

✅ Created by experienced CBSE Science educators

Who Should Use This?

✅ Class 9 CBSE students targeting top scores

✅ Teachers and tutors for test paper prep

✅ Parents helping children with revision

✅ Self-learners looking for structured practice material

Frequently Asked Questions (FAQs)