At a distance of 14.0 m from a point source, the intensity level is measured to be 80 db. at what distance from the source will the intensity level be 40 db

1400m

Explanation:

For spherical waves we can use the following relationship between distance and intensity:

Where and are the first and second intensity, in . And is the first distance:   , and the distace we want to find.

Clearing the previous equation or

.

This is what we will be using to find the answer, but fist we must convert the quantities 80dB and 40dB to

We will call the quantities in dB and :

We will use the following to find the corresponding intensities and :

for both of these: , and it is the minimum intensity that a human being perceives.

Thus, for we have:

And to eliminate the logarithm, we use its inverse operation, exponentiation.

replacing :

and similarly for

replacing :

Now we substitute in the equation we had found for

  the grams     of oxygen gas   that can be produced     is 20.6   grams of o₂

calculation

2liclo₃ →   2 licl + 3 o₂

step 1:   find the moles of liclo₃

moles = mass÷ molar mass

from periodic table the molar mass of liclo₃ =6.9 +35.5   +(16 x3) =90.4 g/mol

moles=38.7 g÷90.4 g/mol=0.4281   moles

step 2:   use the   mole ratio   to calculate the moles of o2

from equation above, liclo₃: o₂   is 2: 3  

therefore the moles of   o₂=0.4281 moles x3/2 =0.6422   moles

step 3: find mass   of o₂

mass= moles x molar mass

from periodic table the   molar mass of   o₂ = 16 x2= 32 g/mol

mass=0.6422   moles   x   32 g/mol = 20.6 grams of o₂