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).

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

1 Hz = 1 vibration per sound = 60 vibration per minute.

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

Ultrasound has frequency of vibration above 20,000 Hz.

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 will be loud when its amplitude is large and sound will be soft when its amplitude is small hence, loudness of sound depends upon its amplitude.

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

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.

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

A violin and a flute may both be played at the same time in an orchestra. Both sounds travel through the same medium, that is, air and arrive at our ear at the same time. Both sounds travel at the same speed irrespective of the source. But the sounds we receive are different. This is due to the different characteristics associated with the sound. Generally, tone and note should be matched in pleasant way. So, the sitarist adjusts the frequency of sitar according to other musical instruments. Only if all the musical instruments are in the same frequency, will the output will be in unison. Otherwise, the music will not be pleasing to the hear’s ears.

According to a report from the World Health Organization a continuous excessive loud noise exhausted your body and nerves of the brain. Excessive loud noise is harmful to us. The presence of excessive noise in the surroundings may cause main health related problems. Loud noise can damage the ear permanently and cause deafness for all young persons or teenagers if they want to hear the loud noise constantly as music.

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].

The ultrasound waves can penetrate into matter to a large extent because they have very high frequency. They have frequency greater than 20,000 Hz.

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

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.

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].

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