Final answer:
If a +5 nC charge has five electric-field lines, a +20 nC charge, being four times greater, would have four times the number of field lines, which is 20 field lines (option d).
Step-by-step explanation:
The question relates to the concept of electric field lines in physics. Electric field lines are a pictorial representation used to visualize electric fields. The number of field lines is proportional to the magnitude of the charge. Therefore, if a +5 nC charge has five electric-field lines, it implies that each field line represents 1 nC of charge.
According to this representation, a +20 nC charge would have four times the number of field lines as a +5 nC charge because +20 nC is four times as much charge as +5 nC. Hence, we would expect:
- 5 lines for +5 nC (as given)
- 5 lines x 4 = 20 field lines for +20 nC
Therefore, the correct answer to the question is d. 20 field lines.