Resistance can be demonstrated through Ohm's Law: R = V/I where R, V, and I refer to resistance, voltage, and current respectively. This equation may be rearranged to provide current with respect to voltage and resistance: I = V/R
If we have a 5V power source which is connected to a 1K resistor for example, the current would equal 5mA. If we increase the resistance of this circuit to 10K, our current then equals .5mA (500 micro-amps). So, when the resistance in a current increases while the voltage remains constant, the current decreases.