I've never been able to understand what factors affect Intensity and Amplitude

[September24]

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Here are some questions from EK 1001 Physics

1. If the amplitude of wave were doubled, the frequency would:
A: Remain same
Explanation: Frequency is independent of amplitude.

2. Which of the following would not increase the intensity of a harmonic wave?
A:Increase in period
Explanation: Intensity is directional proportional to the square of the frequency. Since frequency is inversely related to period, increasing period would decrease intensity.


WHAT?!? I always thought that the one factor that amplitude DIRECTLY affects is intensity. So how can amplitude be independent of frequency but intensity is proportional to it.


What factors influence amplitude and intensity and what factors are independent of it? Aren't pressure intensity and amplitude directly related?

 

[September24]

I did a bit more research and here is what I found

Intensity=p*w^2*A^2*v
Intensity is rate of energy transfer (or power) over surface area
Intensity is increased by density, velocity, amplitude, and angular frequency (Pressure also influences intensity)

So frequency and amplitude both affect intensity. However, frequency and amplitude are both factors of wave SOURCE and don't influence EACH OTHER (frequency is not proportional to amplitude but both increase intensity).

Velocity and density are both factors of density only.


Can anyone confirm if I have this right? Does anything change amplitude at all?

 

[sps27]

That seems to be the case. Amplitude and Angular Frequency are independent of each other while, Amplitude, Intensity, Frequency seem to be related. A conundrum indeed. Here's another list I found on the web. Hope it helps....The intensity of sound depends on:

Amplitude of vibrations of the source.
Surface area of the vibrating source.
Distance of the source from the observer.
Density of the medium in which sound travels form the source.
Presence of other surrounding bodies and
The Motion of the medium.