Important Questions: Sound - Class 8 MCQ

 sound is a mechanical wave that needs a material medium to travel.

The speed of sound in ascending order is minimum in gases, lesser in liquid and maximum in solids.
Gas :- 330-340 m/s
Liquid :- 1500 m/s
Solid :- 5000 m/s

The velocity of sound in solids (railway tracks) is faster than that in air.

The characteristics of a sound are :

(i) Loudness or intensity : it distinguishes between a loud or faint sound , and intensity , depends upon amplitude of sound waves .

(ii) Pitch : it distinguishes a sharp sound from a dull sound and pitch depends upon frequency.

(iii) Quality: it distinguishes between sounds generated by two sources .

Sound is produced by larynx or voice box.

The number of oscillations per second is called the frequency of oscillation, i.e. 50 Hz.

Sound travels the fastest in solids, less in liquids and the least in gases.

Thunder is heard later because the speed of light (flash) is much greater (3×10⁸ms⁻¹) than the speed of sound (330ms⁻¹).

The primary cause for the difference in voices between men, women, and children is the difference in the size and shape of their vocal cords. The vocal cords, located within the larynx (voice box), vibrate to produce sound. In men, the vocal cords are typically longer and thicker, resulting in a lower-pitched voice. In women, the vocal cords are shorter and thinner, leading to a higher-pitched voice. Children have smaller vocal cords compared to adults, contributing to their higher-pitched voices. While factors such as the size and shape of the larynx, lungs, and windpipe also play a role, the primary determinant of voice differences is the vocal cords.

Frequency = 1/time period. 

= 1/unitof time = second⁻¹

Sound depends on the amplitude of the sound wave, distance from the sound source, the density of the medium and the surface area of vibrating bodies.

Pitch of sound depends on its frequency. 

Birds produce sounds by means of a ring of cartilage called syrinx, present at the beginning of their wind pipe. 

Musical sound is produced by regular vibrations whereas noise is produced by irregular vibrations.

Noise pollution is hazardous to health in many ways. Insomnia (lack of sleep), hypertension (high blood pressure) and hearing impairment (temporary or permanent hearing problem) are the effects of noise pollution.

Human beings can hear only within the range of 20 Hz to 20 kHz. So, 100 kHz (1,00,000 Hz) cannot be heard.

The three delicate bones in the middle ear are the hammer, the anvil and the stirrup.

The nerve that carries the signals from the ear to the brain is called the auditory nerve.

Vocal cords are a band of muscles within the larynx. These muscles vibrate to produce the sound.

Frequency is the number of vibrations that pass through a point in space in one second by a body.