Question 134: Waves

Question

A small speaker delivers 2 W of audio output. At what distance from the speaker will one detect 120 dB
intensity sound ? [Given reference intensity of sound as 10
–12
W/m
2
]

Accepted Answer

Sound level = 10$${\log _{10}}\left( {{I \over {{I_0}}}} \right)$$
$$ \Rightarrow $$ 120 = 10$${\log _{10}}\left( {{I \over {{{10}^{ - 12}}}}} \right)$$
$$ \Rightarrow $$ 12 = $${\log _{10}}\left( {{I \over {{{10}^{ - 12}}}}} \right)$$
$$ \Rightarrow $$ 10
12
= $${{I \over {{{10}^{ - 12}}}}}$$
$$ \Rightarrow $$ I = 1 W/m
2
Also we know,
I = $${P \over {4\pi {r^2}}}$$
$$ \Rightarrow $$ 1 = $${2 \over {4\pi {r^2}}}$$
$$ \Rightarrow $$ r = 40 cm

Answer

20 cm

Answer

10 cm

Answer

40 cm

Answer

30 cm

Waves

A small speaker delivers 2 W of audio output. At what distance from the speaker will one detect 120 dB intensity sound ? [Given reference intensity of sound as 10 –12 W/m 2 ]

Choose the correct answer: