Poor Bob is hopelessly lost. Please help him out. a) \"Quiet down! That sound wa
ID: 3278509 • Letter: P
Question
Poor Bob is hopelessly lost. Please help him out. a) "Quiet down! That sound wave's frequency is way too high!" b) The fact that radio waves travel at the same speed as visible light is just a huge cosmic coincidence: radio waves have nothing in common with visible light." Explain why there was an epic battle between Edison's DC plan and Tesla's AC plan for the power grid. In particular, there is a certain device that only works with AC electricity: explain why it only works on AC and why it was the deciding factor in favor of Tesla. State the frequency of your favorite radio station, and then find the wavelength of those radio waves. Determine (a) the amplitude, (b) the wavelength, and (c) speed of the following sound wave. Note that sound is a pressure wave, but the basic description is the same as with light p(x, t) = (2.4 kPa) cos[(15.7m^-1)x - (5338 s^-1)t]Explanation / Answer
1.
(A)Sound wave that can be heard/observed by a healthy human ear ranges from 20Hz to 20,000Hz. It doesnot mean that there exist no sound beyond(ultrasonic)or below(infrasonic) it.
So, as compared to frequency of light(~1015Hz) , frequency of sound is very low, but itself it ranges from low to high frequency.
(B) no it's not a coincidence.
Radio waves are also Electromagnetic waves i.e electric and magnetic fields oscillate perpendicular to the direction of propagation of wave,visible light is also an Electromagnetic wave but with a different frequency and wavelength.
Radio waves have less energy/frequency and larger wavelength as compared to visible light, otherwise they are just the same in form.
All EM waves travel at same speed in vacuum.
3.
Lets say a radio station works on 95.5MHz frequency = 9.55×107Hz.
Speed of light/radio waves in air/vaccuum is 3×108m/sec.
So, formula for wavelength is = speed/frequency.
Wavelength= 3×108ms-1/9.55×107Hz
= 3.141metres
4.
general equation is p = Amplitude [Cos{(2x/wavelength) - (2t*frequency)}]
So, amplitide =2.4kPa.
Wavelength= 2/15.7 m = 0.4188 m
Frequency = 5338/2 = 849.57Hz.