Freshmen are mainly basic courses, such as advanced mathematics and college physics. Since his sophomore year, he began to pave the way for later specialized courses, such as circuit, analog electricity, digital electricity, college physics experiment, line generation, probability statistics, complex variable function and so on. And the junior has begun to further study professional courses, such as electrical engineering, matlab, control motor and so on. And the junior year will also be divided into directions. The teaching requirements of each school are different. I suggest you ask your seniors.