1. 11-9 Energy Transported by Waves
Energy transported by waves is proportional to the square of the amplitude.
Intensity (I) of a wave is defined as the power (or energy per unit of time) transported across unit area perpendicular to the direction of energy flow.
I= power/area= (energy/time)/ area
I= P/4pr2
I is proportional to 1/r2
I2 /I1 = r12 / r22
See Example p330

2. 11-10 Intensity Related to Amplitude and Frequency
E= ½ kA2
E= 2p2mf2 A2
Since m=rV and V=Sl…..
E= 2p2rSltf2 A2
P=E/t =2p2rSlf2 A2
Intensity (I) of a wave is the power transported across unit area perpendicular to the direction of flow…
I=P/S= 2p2rvf2 A2