Final answer:
Voltage and current have a direct relationship as explained by Ohm's law, which holds true only for ohmic materials with constant resistance. This means if resistance is constant and you increase the voltage, the current will also increase proportionally.
Step-by-step explanation:
The relationship between voltage and current is explained by Ohm's law, which states that the current (I) flowing through a material is directly proportional to the voltage (V) applied to it, given that the resistance (R) of the material is constant. Thus, we can say that there is a direct relationship between voltage and current when the resistance remains unchanged. This direct relationship can be mathematically expressed as I = V/R, where I is the current, V is the voltage, and R is the resistance. However, this linear relationship holds true only for ohmic materials where the resistance is constant regardless of the voltage applied. In non-ohmic materials, such as diodes or materials with temperature-dependent resistance, the current does not increase linearly with an increase in voltage.