Question

Gases are bad conductors of electricity. Their conductivity may be increased by (a) increasing the pressure as well as potential difference between the electrodes. (b) decreasing the pressure as well as potential difference between the electrodes. (c) decreasing the pressure and/or increasing the potential difference between the electrodes. (d) increasing the pressure and/or decreasing the potential difference between the electrodes.

Short answer

Option (a): Increasing the pressure and the potential difference between the electrodes increases the conductivity of gases.

Step-by-step solution

- Understanding Gas Conductivity

It's important to recognize that gases are normally poor conductors because their atoms are too far apart to allow free flow of electrons. However, under certain conditions, the conductivity of a gas can increase. These conditions involve altering the pressure and potential difference across the gas.

- Reviewing the Effects of Pressure and Potential Difference

Increasing the pressure of a gas decreases the distance between its particles, which can enhance the likelihood of collision and ionization that leads to increased conductivity. Similarly, increasing the potential difference can provide the energy needed to ionize the gas particles, thereby increasing conductivity. Decreasing these factors would have the opposite effect.

- Analyzing the Options

Option (a) suggests increasing both pressure and potential difference, which both would increase the conductivity. Option (b) suggests decreasing both, which would not lead to an increase. Option (c) presents a mixed approach, decreasing pressure OR increasing potential difference. Only increasing potential difference would help. Option (d) again mixes with one helpful suggestion (increasing pressure) and one unhelpful (decreasing potential difference).

- Determining the Correct Answer

Considering the knowledge from the previous steps, the answer should involve an increase in pressure and/or potential difference. The only option that solely incorporates increasing these conditions to enhance conductivity is option (a).

Key concepts

Electric Conductivity in Gases

When we talk about electric conductivity in gases, it’s essential to begin by recognizing that gases are inherently poor conductors of electricity in their natural state. Why is this? Unlike metals, where electrons can move relatively freely, the electrons in a gas are typically contained within their respective atoms or molecules.

Now, under certain circumstances, this scenario changes. To make a gas conductive, we need free electrons to move through it, which are created when the gas atoms or molecules are ionized. Ionization occurs when an atom or molecule gains or loses an electron, resulting in a charged particle (an ion). Electric fields can then move these ions, allowing electric current to pass through the gas.

What's critical here is the creation of ions, which can be achieved by supplying enough energy to the gas, often in the form of a potential difference (voltage) applied between two electrodes. With enough energy, the gas becomes ionized and thus conductive, the degree of which is measured as its electric conductivity.

Effects of Pressure on Gas Ionization

The effects of pressure on gas ionization are quite fascinating and play a crucial role in the electrical conductivity of gases. At lower pressures, gas molecules are widely spaced, making it less likely for interactions—or collisions—to occur. Without collisions, the opportunity for molecules to become ionized, that is, to lose or gain electrons and form ions, is reduced.

As pressure increases, molecules are pushed closer together. This increased proximity leads to more frequent collisions among the molecules. As a result, when subjected to a sufficient voltage, the chances of electrons being knocked free to create ions — and consequently electric current — are heightened.

In other words, increasing the pressure essentially nudges the gas molecules into a state where the probability of ionization is greater, leading to an increased conductivity. It's like a crowded room where you're more likely to bump into someone; similarly, in a 'crowded' gas, molecules are more likely to bump into each other and ionize.

Potential Difference Impact on Conductivity

Potential difference, often simply called voltage, is a key player in the saga of gas conductivity. Let's compare it to pushing a child on a swing; just as you need to give the swing a push to get the motion started, you need a potential difference to initiate current flow in a gas.

The voltage across the gas provides the necessary energy for electrons to escape from the grip of their parent atoms or molecules—this process is known as ionization. Once free, these electrons can be accelerated by the electric field created by the potential difference, leading to a cascade of collisions and further ionizations known as a Townsend discharge, a phenomenon that significantly boosts the conductivity of the gas.

By increasing the potential difference, we increase the energy supplied to the gas particles, leading to more ionization and, therefore, better conductivity. It's a critical factor, and when it's just right, a gas can transition from an insulator to a conductor—a useful phenomenon in devices like fluorescent lights and plasma screens.