Sound - MCQ Test (22-11-2017) - Class 9 MCQ

Crests and troughs are formed in transverse wave. The upward movement from mean position is called crest and downward movement is called troughs.

Speed of sound is different at different temperature. With increase in temperature, speed of sound increases.The loudness of sound is measured in units called decibels (dB). A decibel unit expresses the relative intensity of sounds on a scale from zero for the average least perceptible sound to about 100 dB, which is near the level most people find uncomfortably loud.

Ultrasound waves vibrate at frequency higher than 20,000Hz. Ultrasonic waves are directed towards kidneys.These waves with such a high vibration break the stones into tiny pieces so they can pass out of the kidney with the urine.

It has been found that the sensation of sound persists in our ears for 0.1 sec or one-tenth of a second,after the original sound dies off.

By further calculation,it is found that to hear an echo,the minimum distance from the sound-reflecting surface must be 17.2 m

X-rays are a form of electromagnetic radiation, as are radio waves, infrared radiation, visible light, ultraviolet radiation and microwaves.These waves do not require material medium for its propagation.

Speed of sound is different at different temperature. With increase in temperature, speed of sound increases.

The loudness of sound is measured in units called decibels (dB). A decibel unit expresses the relative intensity of sounds on a scale from zero for the average least perceptible sound to about 100 dB, which is near the level most people find uncomfortably loud.

Human beings are ultrasound deaf as humans are not able to hear frequency of sound above 20,000 Hz.

Ultrasound travels through various media including gases, liquids and solids, but cannot travel through a vacuum. The speed of sound varies by the medium it travels through. Sound is likely to travel faster through solids, followed by liquids and gases.

The eardrum is a stretched membranous structure at the junction of outer ear and middle ear. Vibration of eardrum causes production of sound that we hear. It is also known as tympanic membrane.

Sound wave is a longitudinal wave as the wave particles of sound travel parallel to the direction of motion by forming compression and rarefaction.

Frequency of infrasonic waves is less than the frequency of ultrasound waves.Frequency of infrasonic waves are less than 20Hz whereas frequency of ultrasonic waves are greater than 20,000Hz.

Animals like dolphins,bats and tortoises produce sounds of frequency higher than 20000 Hz known as ultrasonic sounds.

Cochlea, semicircular canals and auditory nerve are associated with inner ear.The internal ear contains colchea.The vibrating bones pass their vibrations to the colchea.The sensitive hair cells present in the colchea respond to the sound vibrations recieved and change them into nerve impulses.These impulses are then carried by the auditory nerves to the brain.

The maximum displacement of the particles of a mediumfrom their mean position during the propagation of a wave is called the amplitude of the wave. Loudness of sound depends upon amplitude.

The sound whose frequency lies between 20 Hz and 20000 Hz which human beings are able to hear is called audible sound. So,the audible range of human ear is 20-20000 Hz.

Speed of sound = 344ms^-1.

Time taken to hear echo = 0.1s

⟹2×distance=speed×time.

⟹2d=344×0.1

⟹ 2×d=34.4

⟹d=17.2

Therefore,the bat is 17.2 m from its obstacle.

Wave motion is a periodic disturbance in the medium produced by vibrating body. These disturbance moves into medium to produce sounds. Wave motion is also known as propagation of disturbances.

Loudness of sound depends upon amplitude,more the amplitude of a wave, more is the loudness produced.Amplitude is the maximum displacement of a particle from its mean position.

Wavelength is the distance between two consecutive crest or trough in case of transverse wave. Here, distance between the consecutive crest and trough is x, so, wavelength will be 2x.

Sonar stands for Sound navigation and ranging. Sonar is a device that is used to find the depth of the sea,or to locate underwater objects like enemy's submarine,sunken ships,shoal of fish,etc.

Wave motion is activity that carries energy from one place to another without actually moving any matter.In wave motion, energy—the ability to perform work, or to exert force over distance—is transmitted from one place to another without actually moving any matter along the wave. In some types of waves, such as those on the ocean, it might seem as though matter itself has been displaced; that is, it appears that the water has actually moved from its original position. In fact, this is not the case: molecules of water in an ocean wave move up and down, but they do not actually travel with the wave itself. Only the energy is moved.

Electromagnetic waves differ from mechanical waves in that they do not require a medium to propagate. This means that electromagnetic waves can travel not only through air and solid materials, but also through the vacuum of space.

One crest and a trough make a single wavelength.
Therefore,according to the question,20 wavelenghts are made.
Therefore, time = 0.2 sec
Time period=0.2/20 = 0.01 second.
Frequency = 1/time period = 1/0.01 = 100 Hz.

Children under the age of five can hear sound  up to 25,000Hz  which is more than normal adult hearing range. As people grow older their ears become less sensitive to higher frequency.

When a number of echoes of the original sound are heard,each echo being fainter than the preceding one,such multiple echoes are called reverberations. In halls and auditorium reverberation is reduced by using sound absorbing substances.Sound absorbing panels are kept near the stage.

In human ear, the sound is amplified in the middle ear by three bone connected with tympanic membrane. The amplified vibration is transmitted to inner ear and is used to produce sensation of hearing.

Wave motion shifts wave energy from one region to another region. Mass is not transferred during wave motion.

We know that, velocity = distance travelled /time taken
=10 m/0.05 s
= 200m/s.

Now,

Wavelength = wave speed / frequency
⟹200 ms⁻¹/200Hz = 1m.
Therefore,the wavelength of the wave is 1 m.

Bat and porpoises use ultrasound for navigation and location of food in the dark. They contain ultrasound producing organs and receiver that help them to judge the position and location of food and predator.

Music and TV sounds that we hear have noise level below 90 decibels.

An object moving at a speed greater than that of sound is moving with supersonic speed and not ultrasonic speed.

Wave motion transfers energy from one point to another, which displace particles of the transmission medium–that is, with little or no associated mass transport. Waves consist, instead, of oscillations or vibrations (of a physical quantity), around almost fixed locations.

Wavelength= wave speed / frequency, wavelength=440ms⁻¹/840Hz = 0.53m.

Speed of greater than the speed of sound in air is called ultrasonic sound. The amount of sound energy passing each second through unit area is called intensity of sound.