The current passing through an electric circuit is related to the voltage applied across an electric instrument. For example, if you connect a bulb to the battery, the bulb glows, and if you increase the voltage of the battery the bulb glows brighter. Hence, the current flowing through the bulb is directly related to the voltage of the battery. We can determine this relation using a voltage-current graph. The graph has a visible change in slope when we connect different materials across the battery.