Which of the following obeys ohms laws?

1. Analyze the question The question asks which material or device obeys Ohm's law.

2. Explain the concept Ohm's law states that, at constant temperature, the current through a conductor is directly proportional to the potential difference across it:

V = IR (R is constant)

A graph of V against I is a straight line through the origin. Materials or devices that behave this way are called ohmic conductors.

3. Go through the options

• A. Electrolytes: Conduction here involves ions, and the V-I relationship is generally not a straight line because of polarisation and changes at the electrodes. They are not the standard example of Ohmic behaviour.
• B. Metals: At constant temperature, metals give a straight-line V-I graph. They are the classic ohmic conductors.
• C. Diode: It is a non-ohmic device. It conducts well in one direction and hardly at all in the other, so its V-I graph is curved.
• D. Glass: It is an insulator and does not conduct meaningfully, so Ohm's law is not relevant to it.

4. Answer Metals obey Ohm's law, provided the temperature stays constant.

5. Exam tip Remember the non-ohmic examples: diodes, filament bulbs, thermistors, and electrolytes. If a JAMB question asks which one obeys Ohm's law, think "metallic conductor at constant temperature".