1.
What do you mean by mechanical waves?
Mechanical waves are in form of disturbance that travels through the medium due to the periodicmotion of the particles about their mean position, thedisturbance being transferredfromoneparticle to another particle.eg soundwaves,vibration on the string. The medium through which waves propagate should have the property ofvolume elasticity .Not all the waves are mechanical in nature. Waves like light waves,radio waves,x-raysdo not need material medium to propagate.
2.
What was the necessity of Laplace correction in velocity of the sound?
Newton assumed that when sound propagates through the medium compression and rare faction occurs and heat exchanged with surrounding takes place in such a slow manner that temperatureof the medium remains the same and calculated the velocityof sound in the air equal to 280m/s. But the velocity of sound in the air at NTP is foundto be 332m/s, which is greater than the calculated value .so, Laplace corrected thisformula by assuming that propagation of sound takes place through adiabatic process.
3.
If you are walking on the moon, can you hear cracking sound behind you. Explain.
Sound requires medium to travel but on the moon there is no atmosphere and hence no medium so cracking of sound is not heard behind on the moon surface
4.
When sound travels through the medium, the temperature of various points doesn’t remain the same.Explain.
When sound wavespropagates through the air, the compression and rarefaction occurs sorapidly that heatflows neither out of the system to the surroundingsnor heatnor into it, due to whichequilibrium is not maintainedin short periodof time. As a result, temperature of the system doesn’t remain same.
5.
Sound made at a distance can be heard distinctly at night than in day, why?
At night, velocity of sound is more than at day due to reduced density of air. Velocity of the sound is inversely proportional to the square root of density of the medium. Moreover, sound absorbing bodies such as people, vehicles and noise from other sound producing bodies are less at night time as compared to day time. So sound made at a distance can be heard more distinctly at night than at the day time.
6.
Why does the flash of light reach the earth before than the sound coming from the same thunder? Explain.
Although lightning and thunder occur at same time, lightreaches theearth before sound because lightwaves travel at a speed of about 300000km/s whereas sound waves travel at a speed of only about 340m/s which is nearly900000 times smaller than the speed of light.
7.
Why is the velocity of sound greater through moistairthan in dry air?
Density of water vapor is less than density of dry air .In moist air, the presence of humidity reducesthe density. As we have relation between velocity and density i.e. the velocity of sound is inversely proportional to the square root of the density i.e. v α the velocity of sound in moist air is greater than in dry air.
8.
What is the drawback of Newton’sformula for the velocity of sound in a gas?
Newton assumed that sound propagates through the isothermal process and calculated the velocityof sound in the air equal to 280m/s. But the velocity of sound in the air at NTP is found to be 332m/s, which is greater than the calculated value. This was the drawback of the Newton’s formula. Later,Laplace correctedthis formula by assuming that propagation of sound in a gas takes place through adiabatic process.
9.
Explain .Sound travels faster on a rainy day than in a dry day .
Velocity of sound is more in damp air or moist air. We know that the density of damp air is less than dry air due to the presence of humidity. Also we have the relation (v α )i.e. the velocity of sound in air is inversely proportional to the square root density of the medium. So the velocity of sound on a rainy day is more than that on a dry day.
10
In which medium does the sound waves travel faster:solid liquids or gases?Explain.
Velocity of sound depends on the modulus of elasticity. It is given by formula
v =.Although the density of the solid is greater, the elasticity of solid is much greater than the elasticity of the liquid and gases. So, sound travels faster in solid than in liquid or gases. For example,
Velocity of sound in aluminum is 6420m/s
Velocity of sound in air is 332m/s
Velocity of sound in water is 1430m/s.
11
Velocity of sound increases on cloudy day. Why?
On cloudy day, the air is wet. It contains the lot of moisture hence it is less dense. Since the velocity of the sound in air is inversely proportional to the square root of density, velocity of sound increases on cloudy day.
Source:Principle Of Physics Grade 12
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