Class 8 Science Chapter 10 MCQ

Human can also produce sound by vocal cords. The vibration of our vocal cords are small so, we can only feel them with our hands. When we talk, we make sound. When we sing we make sound very easily by our throat or voice box.

Unit of loudness of sound is decibel (dB).

Here, all the statements are correct. Hence, your answer will be option [D].

Loudness of sound is determined by the amplitude of its vibration.

Pitch or shrillness is determined by the frequency of sound.

Because light can travel in vacuum also but it is only sound which requires medium to travel.

Sound requires a medium for propagation. Sound cannot be heard on the surface of moon because there is no air to carry the sound waves. Mass of the moon is 1/100 times and radius of moon is 1/4 times that of the earth. Therefore, the gravitational attraction on the moon is about one sixth of that on the earth. Hence, the weight of an object on the moon is 1/6 th of the weight on the earth not the sound.

Sound requires any medium to travel but in vacuum there is no medium, so sound cannot travel through them.

We know that = Frequency = 1 / Time period Time period = 1 / Frequency = 1 / 50 = 0.02 s

Oscillation = 10, Time taken = 20 s As we know that the number of oscillations per second is frequency. Frequency = No. of oscillations / Time taken = 10 / 20 = 0.5 Hz. Time period = 1 / Frequency = 1 / 0.5 = 2 s

We know that, Distance = Speed x Time = 330 x 5 = 1650 m = 1.65 km (1 km = 1000 m, speed of sound = 330 m/s) So, she is standing at 1.65 km from the place where lighting occurs.

The three tiny bones in the middle part of ear act as a system of levers and sound vibration passing them on the “cochlea” not in brain. Cochlea sets up the vibrations or electrical impulses by auditory nerve to the brain.

Here, all the statements are correct. Hence, your answer will be option [D].

Hearing Aid is a small sound amplifying device worn on the ear by a partially deaf person not deaf person.

Humans are capable of hearing sound waves of frequency between 20 Hz and 20,000 Hz only. This is called the Sonic waves. These audio frequencies are called the audible range. The sound above this range is called ultra-sonic and below it is called sub sonic. Humans are not capable of hearing both the sub sonic and ultra-sonic frequencies. Thus, option [C] 15 kHz and 25 Hz is correct answer because the human audible range is 20Hz to 20,000 Hz.

When the mechanical piano is struck harder the second time, we find sound will be louder but pitch remains the same because the frequency has not changed. The pitch depends on frequency of the particular key which is being hit and hence there would be no change in pitch of sound. In another words, when the key of a mechanical piano struck harder, the vibrations caused are more resulting in larger amplitude of the wave that propagates from the key. Loudness depends on the square of the amplitude of the wave. Amplitude is the size of the vibration, and this determines how loud the sound is. Larger vibrations make a louder sound. Pitch of the sound depends on the frequency of the wave which is not change when the key is struck harder.

Here, all the statements are correct. Hence, your answer will be option [D].

The number of oscillations per second is called the frequency of oscillation. Frequency is expressed in hertz. Its symbol is Hz. A frequency of 1 Hz is one oscillation per second. Speed of highly penetrating ultrasonic waves is greater than 20,000 Hz are known as ultrasonic waves or ultrasound. Speed of the audible and ultra-sonic sound are same but waves lengths are different.

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Timbre or rhythm or modulation can distinguish between the musical sounds produced by different singers on the basis of the characteristic of sound. Sounds may be generally characterized by pitch, loudness, and quality. Sound quality or timbre describes those characteristics of sound which allow the ear to distinguish sounds which have the same pitch and loudness. Timbre is general term for the distinguishable characteristics of a tone. Hence, the quality or timbre of sound is that characteristic which enables us to distinguish one sound from one person to another having the same pitch and loudness

Remember, the speed of sound in liquids is more than gas but less than solids. i)Sound travels at a speed of 5000 meters per second through iron or steel. [Suppose this is M] ii)The speed of sound in air is 340 meters per second. [Suppose this is N] iii) Sound cannot travel in vacuum. [Suppose this is O] iv)The speed of sound in water is 1500 meters per second. [Suppose this is P] Hence, your answer will be option [D] that is P.

Here, all the statements are correct. Hence, your answer will be option [D].

The vocal cords are two bands of smooth muscle tissue found in the larynx. The larynx or the voice box is set in the neck at the top of the trachea (windpipe). The vocal cords vibrate and air passes through the cords from the lungs to produce the sound of your voice. The vocal folds, also known popularly as vocal cords, are composed of twin infoldings of mucous membrane stretched horizontally across the larynx. They vibrate, modulating the flow of air being expelled from the lungs during phonation. The vocal cords in men are about 20mm long. In women these are about 5mm shorter. Children have very short vocal cords. This is the reason why the voices of men, women and children are different.

Here, all the statements are correct. Hence, your answer will be option [D].