This PSEB 8th Class Science Notes Chapter 13 Sound will help you in revision during exams.
PSEB 8th Class Science Notes Chapter 13 Sound
→ Sound is produced by a vibrating object.
→ The maximum distance to which a vibrating body moves on either side from its mean position is called the amplitude of vibration.
→ The time taken to complete one oscillation is called the time period.
→ The number of oscillations per second is called the frequency of oscillation.
→ Frequency is measured in hertz (Hz).
→ The larger the amplitude of vibration, the louder is the sound produced.
→ The higher the frequency of vibration, the higher is the pitch.
→ For human ears, the audible range of frequency is 20 Hz to 20000 Hz.
→ Sound needs a medium for its propagation. It cannot travel in a vacuum.
→ Light travels much faster than sound.
→ The sound may get reflected by an obstacle. The echo is produced due to reflected sound.
→ Some surfaces reflect sound better than others.
→ The pleasant effect of sound on the ear is called music while the unpleasant sound is called noise.
→ In human beings, voice is produced by the vibration of their vocal cords.
→ Amplitude: The maximum distance through which a vibrating body is displaced from its mean position.
→ Echo: The reflection of sound from an obstacle such as a building or a mountain.
→ Frequency: The number of vibrations made by a vibrating body in 1 second.
→ Hertz (Hz): The unit of frequency.
→ Larynx: Organ of voice in human beings.
→ Loudness: The property of sound which depends upon the amplitude and intensity of the vibrating body.
→ Musical Sound: Sound which produces a pleasing effect on the ear.
→ Noise: Sound which produces a disagreeable effect on the ear.
→ Ultrasonic: Vibrations having a frequency above 20,000 Hz.
→ Vibrating Body: An object, moving to and fro about the mean position.
→ Vibrations: To and fro motion of an object.
→ Vocal Cords: Two pairs of membranous cords or folds in the larynx.