How will you know the exponent of scientific notation is negative or positive?

The smaller number at the top right of the ten may or may not have a negative sign in front of it: like 6.2 x 102 or 6.2 x 10-2. If the little number is positive, the decimal in the first number will move to the right. If the exponent is negative, the decimal in the first number will move to the left.