The intensity of a wave at a certain point is I.A second wave has twice the energy density and three times the speed of the first.What is the intensity of the second wave?
A)I
B)2I
C)3I
D)6I
E)2I/3

Question

Quizplus · Accepted Answer

Intensity is directly proportional to the square of the energy density and the square of the velocity. 
Let the energy density and speed of the first wave be E and v respectively. 
Given, the second wave has twice the energy density and three times the speed of the first wave. 
Energy density of the second wave = 2E and speed of the second wave = 3v.
So, 
Intensity of the first wave = E×v² 
Intensity of the second wave = 2E × (3v)² = 18E × v² 
Therefore, the ratio of the intensity of the second wave to the first wave is 
18E × v² / E×v² = 18 
Hence, the intensity of the second wave is 18 times the intensity of the first wave, i.e., 6I.

The Intensity of a Wave at a Certain Point Is