Frank ICSE Solutions for Class 9 Physics – Sound
PAGE NO: 286
Yes, we can hear in the dark room.
Sound is produced by the vibrating objects.
Yes, sound is a form of energy.
No, sound cannot travel through vacuum. It needs a material medium to travel.
Yes, sound requires a material medium for transmission.
The speed of sound depends on the following factors: Density of air, Temperature , Humidity in air as well the wind.
There is no effect on the wavelength and amplitude on the speed of sound.
Speed of sound at room temperature is 330 m/s
Yes, the speed of sound is different in different medium.
No, the speed of sound in the gas is independent on the change in pressure of the gas.
Yes, the speed of sound depends on the direction of wind. When wind is blowing in the direction of propagation of sound , the speed of sound increases. But, when wind blows in the direction opposite to that of sound , the speed of sound decreases.
Ultrasonic are sounds having frequency higher that 20 KHz and not audible to the human being.
SONAR stands for the “SOund Navigation And Ranging”.
Ultrasonic sound has higher frequency than infrasonic sound.
No, we cannot hear the sound produced due to the vibration of second’s pendulum.
No, SONAR does not make use of infrasonic waves. Instead, it make use of ultrasonic waves.
Yes, ultrasound in the medium travels faster than the audible sound.
No, it is not possible to hear the friend’s voice in vacuum because sound needs a material medium to travel.
The following are the requisites of medium to travel:
- The medium should possess elasticity so that particles of medium have tendency to come back to their original position after the displacement.
- The medium should be frictionless so that there should be loss of energy.
- The medium must possess inertia so that particles of medium have ability to store energy.
Sound is produced by the vibrating objects. We require a material medium for the propagation of sound because vibrations of object need to get transferred or transmitted from one place to another.
With increase in temperature of gas, there is increase in speed of gas because increase in temperature decreases the density of gas. And speed of sound is inversely proportional to density of gas. The speed of gas is independent of the pressure of gas.
- No, there is no effect of wavelength and amplitude on the speed of sound.
- With increase in density, there is decrease in the speed of sound in gas.
Sound is defined as form of energy that produces the sensation of hearing in our ears. The sound travels in medium through energy transfers by wave motion from one place to another. For example , when the prong of the tuning fork vibrate , the waves start moving from one fork to another , the air start getting compressed . The compression is pushed forward. Now, when the fork vibrate in another direction, the air in the immediate neighbor which was compressed, now get rarefied. As a result, a series of compression and rarefactions are produced and sound energy travels in the direction where compression and rarefactions travel.
The ratio of speed of sound in air to speed of sound in steel is 1/15.
The distance of observer from the gun = speed of sound x time taken for the explosion = 350 x 2 = 700m
Yes, light travels faster in air than water. Because, light does not require any medium for their propagation and they are not mechanical waves. The quantities which oscillate in light are mechanical and electric field. And electric and magnetic field decrease with the medium in between them. So, light travels faster in air than water.
The flash of light reaches earlier than the sound of thunder because the speed of light (its 3 x 108) is much larger than the speed of sound in air (its 330 m/s).
The sound of 1000 Hz frequency will be audible to us. Others 2Hz is infrasonic sound frequency and 200 KHz, 8 MHz is ultrasonic sound frequency.
There is no atmosphere on moon. So, we cannot hear each other on moon because sound needs a material medium to travel from one place to another. No kind of sound can be heard.
The following are the three characteristics of the medium required for the propagation of sound:
- The medium must possess elasticity so that the particles of medium have the tendency to return back to their original positions.
- The medium must be frictionless so that there is no loss of energy during transmission.
- The medium must possess inertia such that the particles of medium have the ability to store energy.
The simple experiment that a person can do to calculate the speed of sound in air is that a person stands at a known distance (d meter) from the cliff and fires a pistol and simultaneously start the stop watch. He stops the stop-watch as soon as he hears a echo. The distance travelled by the sound during the time (t) seconds is 2d.
So, speed of sound = distance travelled / time taken = 2d/t
Ultrasonics sound is the sound having frequency more than 20KHz. The application of ultrasonic sound is as follows:
- It is used to detect the flaws in metal casting of automobile tyres.
- Used in hospitals to detect defects in certain parts of body.
Sound waves are produced by the object motion back and forth in the medium. Due to which it compresses the medium and compression waves are moved forward. The sound travels in medium through energy transfers by wave motion from one place to another. For example , when the prong of the tuning fork vibrate , the waves start moving from one fork to another , the air start getting compressed . The compression is pushed forward. Now, when the fork vibrate in another direction, the air in the immediate neighbor which was compressed, now get rarefied. As a result, a series of compression and rarefactions are produced and sound energy travels in the direction where compression and rarefactions travel.
Light waves are electromagnetic waves while the sound waves are mechanical waves. Light waves do not require any material medium for their propagation while sound waves need the material medium for its travel from one place to another.
Due to large magnitude of difference between speed of light (i.e 3 x 108 m/s) to the speed of sound in air (330 m/s) , the light reaches first and then the sound from the object. Like, in thunderstorm, the light reaches first to earth and then person hears the sound of light.
- Pressure of air: The speed of sound in air is independent of pressure of air.
- Temperature of Air: Speed of sound in air is directly proportional to the temperature of air. As the temperature of air increases, the density of air decreases and hence speed of sound increases.
- Humidity: The speed of sound increases with increase in humidity. The increase of moisture decreases the density of the atmosphere and therefore sound travels faster in moist air.
- Wind: The speed of sound depends on the direction of wind. When the wind is blowing in the direction of propagation of sound, the speed of sound increases. But, when the wind blows in the direction opposite to that of the sound, the speed of sound decreases.
- The bat during its flight at night: Bats emits its own distinctive sounds. The echoes of the sound helps bat to navigate and to locate their prey during night.
- The dolphin to locate small fish as its prey: Dolphins sends the sound having frequencies between 120 KHz to 150KHz. The returning echoes used to help their preys.
A person hearing at one end of the long metal bar hears two distinct sounds when the other end is struck with a stone because sound comes from the metal bar as well as from air. The sound travels faster in solids than air. So, first sound comes from metal bar hitting and then from air.