Air can act as both an insulator and a conductor. Consider reaching for a metal doorknob after scuffing your feet over a carpet. As your hand approaches the knob, a spark jumps between your hand and the knob. Explain how air acts as both insulator and conductor in this situation.
The correct answer and explanation is :
Air is generally an insulator, meaning it does not easily allow the flow of electric current. However, under certain conditions, it can become a conductor, allowing electricity to pass through. The scenario of touching a metal doorknob after scuffing feet on a carpet illustrates how air can transition between these two states.
Explanation:
- Air as an Insulator:
Under normal conditions, air acts as an insulator because its molecules do not readily conduct electricity. The electrons in the air molecules are tightly bound, preventing the free movement of charge. This is why we do not normally see electrical discharges in everyday situations. - Charge Buildup on the Body:
When you scuff your feet on a carpet, you generate static electricity through friction. This process, known as triboelectric charging, causes electrons to transfer between the carpet and your body. If you accumulate an excess of electrons, you become negatively charged. - Breakdown of Air’s Insulating Properties:
As your hand moves closer to the metal doorknob, the electric field between your charged body and the neutral knob strengthens. If the field becomes strong enough (typically exceeding 3,000,000 volts per meter), it ionizes the nearby air molecules, stripping electrons from atoms and creating plasma. This ionized air is now a conductor. - Air as a Conductor – The Spark:
Once ionization occurs, the air becomes momentarily conductive, allowing electrons to rapidly move from your hand to the doorknob. This sudden movement of charge is seen as a visible spark and felt as a small shock.
Conclusion:
Air is an insulator under normal conditions but can become a conductor when the electric field is strong enough to ionize its molecules. This explains why a spark jumps between your hand and the doorknob after scuffing your feet on a carpet.