This document discusses electromagnetic radiation and its properties. It defines electromagnetic radiation as a form of energy that exhibits both wave and particle properties. As a wave, electromagnetic radiation is characterized by its frequency, wavelength, and amplitude. Higher frequency radiation like gamma rays and X-rays have shorter wavelengths and higher energies, allowing them to penetrate deeper into materials. Exposure to high energy radiation can be dangerous by breaking molecular bonds through ionization. Electromagnetic radiation can also be described by photon particles, where the energy of each photon is determined by Planck's constant and the radiation's frequency or wavelength.

1. ELECTROMAGNETIC
RADIATION

2. ELECTROMAGNETIC RADIATION
•Definition – a form of energy generated
through free pace or through a medium in the
form of electromagnetic waves. It includes
radio waves, microwaves, infrared, visible light,
ultraviolet, X-rays and gamma rays.
•Electromagnetic radiation is dual in nature – it
exhibits wave properties and particulate

3. WAVE PROPERTIES

4. WAVE PROPERTIES
•Waves are characterised by frequency,
wavelength and amplitude
• Frequency (ν) – is the number of waves (cycles) per
second
• Wavelength (λ) – is the distance between two
consecutive peaks or troughs in a wave
• Wavenumber (ν͠ ) – the number of waves crests (or troughs) in
a given length

5. WAVE PROPERTIES
amplitude

6. WAVE PROPERTIES
Important units
• Wavenumber ( ν͠ ) – cm-1
• Wavelength (λ) – m,
-Angstrom (A)- 1 x 10-10
m
-Nanometre (nm)- 1 x 10-
9 m
-Micrometre (µm)- 1 x
10-6 m
• Frequency (ν) – Hz = 1/s
= s-1
Constants and equations
• Speed of light (c) – 3.0 x 108
ms-1
(in a vacuum)
• Planck’s constant (h) -6.63 x
10-34 Js
•ν͠ = ν/c = 1/λ

7. PARTICULATE (PHOTON)
PROPERTIES
•Radiation can also be described in
terms of particles of energy called
photons.
•The energy of a photon is determined
by
E = hν = h c/λ

8. WORKED EXAMPLE
1.a) Calculate the energy (E) of a
quantum of radiation with a
corresponding frequency (ν) of 4.57 x
1014 Hz.
b) using the energy (E), determine the
wavelength (λ) that corresponds to the above
frequency.

9. WORKED EXAMPLE
a) E = hν
֒ 6.63 x 10-34 Js x 4.57 x 1014
s-1
= 3.03 x 10-19 J
Note: 1 Hz = 1s-1
b) E = h c/λ
֒ λ = hc/E
(6.63 x 10-34 Js x 3.0 x 108 ms-1) ÷ 3.03
x 10-19 J
= 6.564 x 10-7m

10. CALCULATION HOMEWORK
1.What is the frequency of red light with a
wavelength of 690.nm?
2.What is the wavelength of light in nm, that has a
frequency of 6.6 x 1014 Hz?
3.How much energy does a photon of light with a
frequency of 4.60 x 1014 s-1 have?
4.How much energy does a photon of Red light with
a wavelength of 690.nm?

11. THE ELECTROMAGNETIC SPECTRUM

12. THE ELECTROMAGNETIC SPECTRUM
Category Range of
Wavelength (nm)
Frequency (Hz)
NB: 1Hz = s-1
Energy
Gamma
rays
<1 > 3 x 1017
X-rays 1-10 3 x 1016 – 3 x 1017
Ultraviolet
light (UV)
10- 400 7.5x1014 – 3 x 1016
Visible
light
400- 700 4.3x1014 –7.5x1014
Infrared 700- 105 3 x 1012 – 4.3x1014
microwave 105- 108 3 x 109 – 3 x 1012
Radio >108 < 3 x 109
increases
decreases
decreases

13. DANGERS OF HIGH ENERGY WAVELENGTHS PENETRATING ABILITY
OF EM RADIATION
• Different frequencies of EM radiation have different degrees of
penetration. For example, if we take the human body as the object,
visible light is reflected off the surface of the human body, ultra-violet
light (from sunlight) damages the skin, but X-rays are able to penetrate
the skin and bone and allow for pictures of the inside of the human
body to be taken.
• If we compare the energy of visible light to the energy of X-rays, we
find that X-rays have a much higher energy. Usually, electromagnetic
radiation with higher (energy) have a higher degree of penetration than
those with low frequency.
• Certain kinds of electromagnetic radiation such as ultra-violet
radiation, X-rays and gamma rays are very dangerous. Radiation such
as these are called ionising radiation. Ionising radiation transfers
energy as it passes through matter, breaking molecular bonds and
creating ions.
• Excessive exposure to radiation, including sunlight, X-rays and all

14. ENERGY LEVELS IN ATOMS AND MOLECULES
• E = hν also useful in calculating the energy of a quantum of radiation in an
atom or molecule.
• Recall the assumption that electrons in an atom only exist at
certain energy levels and energy levels are fixed (quantised)
• When sufficient energy is supplied an electron can be promoted
(excited) from a lower energy level to a higher one.
• The electron is unstable at a higher energy level and emits
(releases) the excess energy (as radiation) to return to the lower
energy level.
• If the frequencies that correspond to the radiation emitted falls
within the visible region, the radiation will have colour.