Question

The resistance of a discharge tube is

• A. non-ohmic
• B. ohmic
• C. zero
• D. both (b) and (c)

Answer 1

The Correct Option is A

The question concerns the resistance of a discharge tube. To answer this, we need to understand the characteristics of such a tube.

A discharge tube is a closed glass tube containing a gas at low pressure through which an electric current is passed. When a high voltage is applied, the gas ionizes, allowing the current to flow. The behavior of current and voltage in such a tube does not follow Ohm's Law, which is the fundamental characteristic of ohmic conductors.

Here's the logical breakdown of the options presented:

• Ohmic: According to Ohm's Law, current through a conductor between two points is directly proportional to the voltage across the two points. Ohmic conductors have a constant resistance. This does not apply to a discharge tube whose resistance changes with the applied voltage.
• Non-ohmic: Discharge tubes do not follow Ohm's Law since their resistance changes as the current passes through different stages of ionization. They exhibit non-linear current-voltage characteristics. Hence, the resistance of a discharge tube is non-ohmic.
• Zero: If the resistance were zero, the discharge tube would act as a superconductor, which is not typically the case here.
• Both (b) and (c): This option is incorrect because while resistance might not follow Ohm's Law, it is not zero either.

In conclusion, the most appropriate answer is non-ohmic.