Answer: the smaller particles will move further down the gel
Explanation:
DNA is negatively charged because of the negative charges on the phosphate backbone. What you do in an electrophoresis is basically put DNA particles in something similar to Jello, and then put a positive charge at the far end of the gel.
All of the negatively charged DNA is attracted to the positive far end. However, the smaller pieces of DNA will be less tangled in the gel, and can reach the end much quicker.
This allows you to determine the large vs smaller particles basically
