2. What is the electromagnetic
spectrum?
The electromagnetic spectrum is the range of frequencies of electromagnetic
radiation and their respective wavelengths and photon energies.
This frequency range is divided into separate bands, and the electromagnetic
waves within each frequency band are called by different names; beginning at the
low frequency (long wavelength) end of the spectrum these are: radio
waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays at
the high-frequency (short wavelength) end.
The electromagnetic waves in each of these bands have different characteristics,
such as how they are produced, how they interact with matter, and their practical
applications.Gamma rays, X-rays, and high ultraviolet are classified as ionizing
radiation as their photons have enough energy to ionize atoms, causing chemical
reactions.
A technique called spectroscopy can be used to physically separate waves of
different frequencies, producing a spectrum showing the constituent frequencies.
Spectroscopy is used to study the interactions of electromagnetic waves with
matter.
3. Radio waves
Radio waves are generated by accelerated
electric chargers in metal poles.
Their main use is radio communication and
broadcasting to transmit sounds and images
at long distances.
The once with longer wavelengths can
overcome big obstacles thanks to diffraction.
Radio waves with shorter wavelengths can
only be detected if the receiving antenna is
on a line of sight with the emitting antenna.
Nowadays it is also possible to use artificial
satellites that receive the signal and reflect it
even from one hemisphere to the other.
4. Microwaves
Microwaves can exclusively be generated with special electron tubes. Inside these tubes, electromagnetic radiation is produced by a flow of free
electrons moving at a carefully modulated speed.
A small interval around 2,45x10!
Hz of microwaves are absorbed by water molecules so this energy transfer allows us to heat, defrost or cook food
quickly and uniformly.
Radars use microwaves reflection to detect the presence of an obstacle or to determinate its position in the dark, in foggy weather or between clouds.
They can, also, be used to send telegraph of telephone signals with little power. Their disadvantages that their propagation is limited by obstacles so
repeaters are necessary.
5. Laboratory
Materials:
- Microwave
- Chocolate
Open the microwave over and take out the rotating plate.
Put a dish in the oven and position it upside down, then put
the chocolate onto the dish, this way the chocolate will not
rotate when your start the oven.
Heat the chocolate for 15-20 seconds, as soon as its start
melting turn off the oven and take out chocolate. Then
measure the distance between the melted areas.
Multiply the distance by 2 and by the frequency of your
oven in Hz. You should obtain a figure close to the speed
of light (299792458 m/s)
4,5x2x2,96⍨c
6. Infrared radiation
Infrared radiation is positioned between microwaves and
visible red light.
This radiation is mainly produced by thermal emissions.
Molecules also easily absorb these radiations that cause
an increase in their vibration motion and, therefore, an
increase in the temperature of bodies exposed to infrared
radiation.
Carbon dioxide are transparent to visible sunlight, but
absorb the earth’s infrared radiation so man-made
increase in carbon dioxide limits energy dissipation and
causes the greenhouse effect.
7. Ultraviolet radiation
Ultraviolet radiation (UV) is invisible to the human eye, but it
can impress photographic plates and cause phosphorescence
in some bodies.
Some substances can absorb UV radiation and reemit radiation
at a different wavelength: this phenomenon is called
phosphorescence.
They can be generated with electric dischargers in tubes
containing rarefied gas.
8. X-rays
Wilhelm Conrad Röntgen, in 1895,
discovered X-rays by accident while he
was investigating cathode rays using a
vacuum tube.
He noticed the shadow of the bones of
his own hand, and realized he had
discovered rays that are able to pass
through human tissue are generated
every time high-energy electron beams
are stopped by matter.
9. Gamma rays
Gamma rays are at the lower limit of the of the electromagnetic spectrum.
This is spontaneously emitted by the nuclei of radioactive atoms. The nuclei of these isotopes are unstable and they transform into nuclei of other elements emitting
radiation.
There are 3 types:
- Alpha radiations are made of helium nuclei
- Beta radiations are electrons that, instead of orbiting around the nucleus, are generated inside it
- Gama radiations are electromagnetic radiations and, to absorb them almost completely, it is necessary to use a lead shield several centimeters thicks
10. Team Work
Mario Nicola Mazziota and Francesco Loparco
have been analyzing the Moon’s gamma-ray
glow to understand the fast-moving particles
called cosmic rays.
“Seen at these energies, the Moon would
never go through its monthly cycle of phases
and would always look full” said Loparco.
Although the gamma-ray Moon doesn’t show
a monthly cycle of phases, its brightness
does change over time: Moon’s brightness
varies by about 20% over the Sun’s 11-year
activity cycle.
The Fermi gamma-ray space
Telescope is a space observatory
being used to perform gamma-ray
astronomy observations from low
Earth orbit. Its main instrument for
studying astrophysical and
cosmological phenomena such as
active galactic nuclei, pulsars, other
high-energy sources and dark matter.
Cieplinski Zoe-Di Clemente Giorgia-Di Luzio Sara-Sacchetti Ludovica
5°E
