Question

PHYSICS SELF TEST V 1. A source of sound emits 10.0 watts at the very centre of a spherical glass ball of radius 1.00 m. a) How much power passes through the whole sphere? b) What is the intensity of sound at the glass sphere? c) How much power passes through a 1.0 m2 portion of the sphere? 2. The same source as in (1) is now placed at the centre of a glass sphere that has a radius of 10.0 m. a) How much power passes through the whole sphere? b) What is the intensity of sound at the glass sphere? (c) How much power passes through a 10 cm x 10 cm area on t sphere? (assume two significant digits)

Answer 1

(1)(a) 10 W

(b) ​​​
I = P/(477
​​​
10/(4m(lm)

= 0.796 W/m²

(c) P = I A = 0.796 × 1

= 0.796 W

(2) (a) 10 W

(b) =  0.00796 W/m²

I = P/(477) = 10/(47(104))

(c) Area = A = 10 cm × 10 cm

= 0.1 m × 0.1 m

= 0.01 m²

P = IA = 0.00796 × 0.01

= 8.0 × 10^-5 W