CBSE Class 12-science Answered

1. Let's suppose you want to find the log of 72.98.

Characteristic = 1   (2 digits before decimal. therefore, 2-1=1)

For mantissa, read from the table a number 7298. From the rows, choose 72, and read off from the number under the column 9. The number given in the log tables is 8627. Now read, in the same row, the mean difference under 8. This number is given as 5.

Mantissa = 8627 + 5  = 8632

Thus log 72.98  = Characteristic of 72.98   +   Mantissa of 72.98

                       = 1   +   0.8632

                       = 1.8632

2. Find the log of 500.2.

Characteristic = 2   (3 digits before decimal. therefore, 3-1=2)

For mantissa, read from the table a number 5002. From the rows, choose 50, and read off from the number under the column 0. The number given in the log tables is 6990. Now read, in the same row, the mean difference under 2. This number is given as 2.

Mantissa = 6990 + 2  =  6992

Thus log 500.2  = Characteristic of 500.2   +    Mantissa of 500.2

                       = 2   +   0.6992  

                       = 2.6992