An ohmic conductor has current directly proportional to potential difference when temperature is constant. Its current–potential difference graph is a straight line through the origin. Use V = IR; on an I-against-V graph, a steeper gradient means a smaller resistance. Example: An I-against-V graph is straight through the origin. State the condition needed before claiming Ohm’s law. Temperature must be constant; current is then directly proportional to potential difference. Link cause and effect.