Hc Verma Solutions Class 12 Chapter 19 Electric Current Through Gases

HC Verma Solutions for Concepts of Physics Vol. 2, Chapter 19 - Electric Current through Gases. This chapter deals with the fundamental understanding of electric discharge through gases, plasma state, and its applications.

HC Verma Solutions Chapter 19: Electric Current through Gases

Key Topics Covered in the Chapter:

1. Ionization and Discharge:
   • Ionization by collisions
   • Role of electric fields in ionization
   • Avalanche effect
2. Electrical Conduction in Gases:
   • Townsend discharge
   • Characteristics of gas discharge
   • Breakdown voltage and Paschen's Law
3. Glow Discharge and Arc Discharge:
   • Properties of glow discharge
   • Transition from glow to arc discharge
   • Applications in devices like fluorescent lamps
4. Plasma:
   • Definition and properties
   • Plasma as the fourth state of matter
   • Examples of plasma in nature (e.g., stars, lightning)

Exercise Solutions

Objective I

1. Multiple-choice questions covering ionization, breakdown voltage, and Paschen's Law.
2. Questions on understanding glow discharge and plasma concepts.

Example:

• Question: What happens to the breakdown voltage in a gas as the pressure decreases significantly?
  Answer: It first decreases and then increases (explained by Paschen's Law).

Objective II

1. Multiple-select questions to identify correct statements about gas discharge phenomena.

Example:

• Question: Select all correct options about plasma:
  a) Plasma is a good conductor of electricity.
  b) Plasma consists of neutral molecules only.
  c) Plasma exists in fluorescent tubes.
  d) Plasma is the most abundant state of matter in the universe.
  Answer: a, c, and d.

Exercise Questions (Subjective Solutions)

1. Descriptive Problems:
   • Derive the relation for Paschen's Law.
   • Explain the working of a gas discharge tube.
2. Numerical Problems:
   • Calculate the breakdown voltage for a gas given specific parameters.
   • Determine the electron energy required for ionization of a given gas molecule.

Example Numerical:

• Question: Calculate the breakdown voltage of helium gas at a pressure of $1 \, \text{mmHg}$ and electrode spacing of $2 \, \text{cm}$, given that Paschen's constant $p \cdot d = 10 \, \text{Torr-cm}$.
  Solution: Use Paschen's Law $V_b = f(p \cdot d)$.

Additional Practice:

1. Sketch the characteristic curve of a glow discharge tube.
2. Discuss the differences between glow discharge and arc discharge.

Applications Discussed

1. Cathode ray tubes.
2. Fluorescent lamps.
3. Neon lights.
4. Plasma displays.