The "K" rating for copper is 12.9 and aluminum is 21.2. This video shows copper rated at 12, this is incorrect. The reason I used 12 is because I went to school for this and they taught me the number was 12. This is why it is always good to double check what you are being taught to make sure it is correct.
This lesson teaches then how to create the formulas for Voltage Drop from just one foundational formula. There are questions at the end to test how well you comprehended this.