Help calculating decibel level from intensity of sound

[RichardGib]

Homework Statement

Determine the decibel rating of the following intensities of sound.

I = 1.0 x 10-5 W/m2

Homework Equations

The equation which relates the intensity of a sound wave to its decibel level is:

dB = 10 * log( I / 1.0 x 10-12 W/m2)

The Attempt at a Solution

dB = 10 * log( 1 x 10-5 W/m2 / 1.0 x 10-12 W/m2) = ?

I put it into my calculator and can't actually get an answer out of it. I know the answer is 70dB as I looked in the answer booklet but I couldn't get that answer by entering the equation into it?

Any help would be greatly appreciated. Thanks

 

[Doug Huffman]

It's right there, 10(12 - 5)=70 by inspection.

 

[RichardGib]

It's right there, 10(12 - 5)=70 by inspection.

Thankyou. How would this one be worked out? I am very new to physics so equations are confusing at the moment:

dB = 10 * log( 6.1 x 10-6 W/m2 / 1.0 x 10-12 W/m2) = 68 dB

How would that be inputted into a calculator?

Thank you very much :)

 

[Doug Huffman]

LOL Sorry, I haven't used a calculator in many years.

My collection of calculators (HP-35, 41, 48) live in the same box with a half-dozen slide rules.

 

[RichardGib]

LOL Sorry, I haven't used a calculator in many years.

No worries. Thank you for your help!