There are Reasons for success but failures have no reasons they are excuses. "I could not because..." has no taker. As an engineer you are expected to clear the subjects. The electrical subject in B.E is just an extension of 12th Physics. So do put your hard work to get it cleared soon. a Back log is a Backlog . The sooner that is wiped off, the better it is. If you find it difficult, put an extra effort. The affect of a backlog varies from company to company and many companies just dont like it! Dont be scared. Just clear it.