What is the relationship between voltage and current?

You need to figure in resistance also. The formula is I=E/R. Current (I) = Voltage (E) divided by Resistance (R). At the same resistance, if voltage goes up, so does current.

The ratio of voltage (U) to current (I) is called 'resistance', i.e: R = U/I. If this ratio is constant for variations in voltage, then the circuit is said to be 'linear' or 'ohmic', and obeys Ohm's Law. If the ratio changes for variations in voltage, then the circuit is said to be 'non-linear' or 'non-ohmic', and the circuit does not obey Ohm's Law. As most circuits are non-linear, it is clear that Ohm's Law is not a universal law.