Introduction:
When it comes to calculating interest on a sum of money, there are two types of interest - simple interest and compound interest. In this case, we need to find the difference between simple interest and compound interest on a principal amount of ₹20000 at an interest rate of 8% per annum.

Simple Interest:
Simple interest is calculated based on the principal amount, the interest rate, and the time period. The formula to calculate simple interest is given by:
Simple Interest = (Principal * Rate * Time) / 100

In this case, the principal amount is ₹20000, the interest rate is 8% per annum, and we need to find the simple interest for a certain period of time. Let's assume the time period is 2 years.

Substituting the values into the formula, we get:
Simple Interest = (20000 * 8 * 2) / 100 = ₹3200

Compound Interest:
Compound interest is calculated based on the principal amount, the interest rate, the time period, and the compounding frequency. The formula to calculate compound interest is given by:
Compound Interest = Principal * (1 + Rate/100)^Time - Principal

In this case, the principal amount is ₹20000, the interest rate is 8% per annum, and we need to find the compound interest for a certain period of time. Let's assume the time period is 2 years and the interest is compounded annually.

Substituting the values into the formula, we get:
Compound Interest = 20000 * (1 + 8/100)^2 - 20000 = ₹3328

Difference:
To find the difference between simple interest and compound interest, we subtract the simple interest from the compound interest.

Difference = Compound Interest - Simple Interest = ₹3328 - ₹3200 = ₹128

Conclusion:
Therefore, the difference between simple interest and compound interest on ₹20000 at an interest rate of 8% per annum for a time period of 2 years is ₹128.