ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: Thelimz on August 24, 2011, 03:46:43 pm

Title: sound: finding power of source
Post by: Thelimz on August 24, 2011, 03:46:43 pm: 3 m away from a speaker, the intensity is 0.71 Wm^-2. What is the power of the source?
Title: Re: sound: finding power of source
Post by: mardat on August 24, 2011, 04:32:56 pm: The formula to use is I=P/A where I is intensity, P is power, and A is area. Given you want to find power, you can re-arrange that equation to P the subject -> P=I*A. Then sub in values. I is 0.71, and A is 4*pi*r^2 (The surface area of a sphere) where r is the distance from the speaker, i.e. 3. That formula will give you P=0.71*4*pi*3^2 = 80.30W
Title: Re: sound: finding power of source
Post by: Lasercookie on August 24, 2011, 04:34:04 pm: intensity = power/area
Sound intensity is the ratio of the sound power to the surface area of a sphere of radius r. (think about the shape of a wave)

$I = P/A$

$P = I*A$

Surface area of sphere: $A = 4 \pi r^2$

$P = 0.71 * 4\pi3^2$
$P = 0.71 * 4\pi9$
$P = 80.3 W$

Let me know if this is correct.

edit: damn, beaten :(