Electromagnetic Radiation:
Transmission of energy
through space without
physical connection through
varying electric and
magnetic fields
What’s light?
Light, is the smallest quantity of energy that can be transported.
A photon, an elementary particle without a real size That can’t be split, only created or destroyed.
Light also has a wave-particle duality being kind of a particle and a wave at the same time (although this is a lie) therefore, light is an electromagnetic wave.
Electromagnetic waves
Oscillating electric and magnetic
fields. Changing electric field creates magnetic field, and
vice versa. They can travel in a vacuum and are created by accelerating charged particles.
Speed of light(c)
C=3.0e8 m/s
Wave motion
transmits energy without the physical
transport of material
Electromagnetic waves need no medium. It moves fastest in
empty space.
Frequency
number of wave crests that
pass a given point per second
Period
time between passage of
successive crests
Wavelength
distance between successive crests
Velocity
speed at which crests move
Relationship c=lambda/frequency
Longer wavelength=?
Smaller wavelength=?
Smaller frequency
Greater frequency
How does light and matter interact?
Emission
• Absorption
• Transmission:
— Transparent objects transmit light.
Opaque objects block (absorb) light.
• Reflection or scattering
- we see by scattered light
What about black objects? Why do they look black?
Interactions between light and matter determine the appearance of everything around us.
Thermal Energy light production
all objects emit thermal radiation
including planets, stars…etc
• Objects around us like desk,
stone, rock, gas….etc, and human
body emit radiation
This part
• An object thermal radiation
(glowing) emits
visible radiation
spectrum depends only on one
property: Temperature.
As the surface temperature increases..
the wavelength changes.
• It will glow red and eventually yellow → white → blueish
Ascending temperature
Thermal Radiation
•An object at any temperature is known to emit thermal radiation.
• Characteristics depend on the temperature and surface properties.
• The thermal radiation consists of a continuous distribution of wavelengths
from all portions of the EM spectrum
Properties of thermal radiation
Hotter objects emit more light at all frequencies per unit area.
Black body radiation
•A black body is an ideal system that absorbs all
radiation incident on it.
•The electromagnetic radiation emitted by a black
body is called blackbody radiation.
Intensity of black body radiation
•The intensity increases with
increasing temperature.
•The amount of radiation
emitted increases with
increasing temperature.
• The area under the curve
•The peak wavelength
decreases with increasing
temperature.
Max Planck
Max Planck = Photon energy
•Introduced the concept of “quantum
of action”
•In 1918, Max Planck was awarded
the Nobel Prize for the discovery of
the quantized nature of energy
•Energy E is emitted in discrete
quantities and depends on the
frequency of radiation, f
E = hf
Planck’s constant
h = 6.63x10-34 J.s
Energy of an oscillator
•The energy of an oscillator can have only
certain discrete values En.
En = n h ƒ
• n is a positive integer called the quantum
number
• ƒ is the frequency of oscillation
• h is Planck’s constant
• This says the energy is quantized.
• Each discrete energy value corresponds to a
different quantum state.
• Each quantum state is represented by the quantum
number, n.
What’s a photon?
What is a photon?
A photon is a piece or packet of energy
▪ has no mass
▪ Moves at speed of light, c
▪ Acts like a particle
▪ Has momentum
▪ Has quantized energy
𝒉𝒄
Energy of photon, E=hf=hc/lambda
Momentum of photon, p=h/lambda
Name types of electromagnetic waves from ascending order of wavelength and descending order of energy per photon
Gamma ray, x-ray, ultraviolet, visible light, infrared, microwave, radio
