Emission of Light from
Gases
Gas discharge lamps are
demonstrated
Purpose
To produce light from a gas and
electricity
Demonstration
Gas discharge tube
An electric power
source was attached to
the ends of a glass tube
filled with a gas.
The current was turned
on and electricity ran
through the tube
exciting the gas.
Light was emitted.
Three Concepts of
Emission
Atomic Emission
Spectrum of Light
Energy States
Atomic Emission
When an electric current is passed through a
gas, the gas emits light.
This is due to the change of energy of the
gas. The electrons in the atoms of the gas
become excited to a higher energy state (the
“excited state”) and when they return to the
original, low-energy state (“the ground state”),
the atoms of the gas emit the excess energy
as light.
Spectra
Spectra (plural of spectrum) are composed of
different energies which continuously change
from high to low. A rainbow is a spectrum of
different color and light energies.
The color of the light is determined by the energy
of the emitted light, and the energy is related to
the wavelength
Different colors are due to different wavelengths
of light
Different colors therefore are of different energy
Color Spectrum
High Energy
Low Energy
Energy States of Atoms
Ground state - the lowest energy state of an
atom or molecule (most stable state) with
regard to the position of the electrons around
the nucleus
Excited state – results when ground state
electrons are excited by energy to higher
energy states. Excited states are unstable
and an atom in the excited state immediately
returns to the ground state.
Conclusion
A power supply attached to a gas discharge
tube will send an electric current from one
electrode, through the gas, to the other
electrode.
This excites the gas atoms to their excited
state, and in turn they return to the ground
state and emit a color of light depending on
the energy released.
Comments
Neon signs that you see all over town
work upon the concept of gas discharge
lamps. The different colors of the signs
are from either using different gases or
colored tubes.
Fluorescent lights are similar but are
coated inside with a chemical that emits
light in the presence of electrical energy
Quiz
Would changing the gas inside the tube affect the color of light
emitted?
When the current of electricity runs through the tube do the
atoms have a higher energy or lower?
Is the wavelength proportional to the energy released?
When does the atom release the energy as light - in the ground
state or in the higher energy state?
What is a common use for gas discharge lamps?