In realistic world there are so many examples which use exponential and logarithmic functions.
Use of Logarithmic function
We can find use of logarithmic function in measuring earthquake (Richter Scale) , the brightness of stars , and chemistry(pH balance , measure of acidity and alkalinity)
For example:
In Richter Scale , a logarithmic function that is used to measure the magnitude of earthquake.
If A = measure of amplitude of earthquake wave.

= Amplitude of smallest detectable wave.
From this we can find R the Richter scale measure of magnitude of earthquake.
Use of Exponential Function:Exponential function may use in finding compound interest , population growth , radioactivity decay , etc.
For example :
As we know the formula for compound interest is

Where P is principal amount , r = rate of interest(decimal) , n is the number of compounding period , t is time.
For