Final answer:
The current density could be low due to either high resistance or low voltage in the conductor, as both would result in a decreased current according to Ohm's Law.
Step-by-step explanation:
The root of the question is to identify which factor influences current density. Current density is related to both the current flowing through a conductor and the conductor's cross-sectional area. According to Ohm's Law, current density is directly proportional to the electric field, which is the result of the applied voltage over the conductor. Therefore, a high resistance will oppose the flow of electrons more than a low resistance, leading to a smaller current for a given voltage. On the other hand, a higher voltage for a given resistance will drive a higher current and therefore a higher current density.
If we were to address the question directly, the reason for the current density being blank could be due to either low voltage or high resistance, as both scenarios would lead to a lower current. However, without additional context or the specific measurements in the question, we cannot determine which one is the cause.