Real-World Applications of Logarithmic Functions
Before beginning this tutorial, you may wish to review the tutorial on Arithmetic With Numbers In Scientific Notation.
In chemistry, a solution’s pH is defined by the logarithmic equation , where t is the hydronium ion concentration in moles per liter. We usually round pH values to the nearest tenth.
a. Find the pH of a solution with hydronium ion concentration 4.5 x 10-5
b. Find the hydronium ion concentration of pure water, which has a pH of 7.
- If t=4.5 x 10-5, then p(t)= -log10(4.5 x 10-5)= -(log104.5 + log1010-5)= -(log104.5 + (-5)(log1010))= -(.6532+-5)= -(-4.3468)=4.3.
- Since water has a pH of 7, we know 7=-log10t and so 7=log10t-1; thus 107= t-1, and so the hydronium ion concentration of water is t=10-7 moles per liter.
Measuring decibels of sound
The loudness of sound is measured in units called decibels. These units are measured by first assigning an intensity I0 to a very soft sound (which is called the threshold sound). The sound we wish to measure is assigned an intensity I, and we measure the decibel rating d of this sound with the equation .
- Find the decibel rating of a sound with intensity 5000I0.
- If a sound has a decibel rating of 85, how much more intense is it than the threshold sound?
a. = decibels
b. , where the sound in question is k times as intense as
the threshold sound. Thus , and so the sound is
times as intense as the threshold sound.