Ultraviolet waves
Ultraviolet waves have wavelengths shorter than violet light—so our eyes cannot
detect them—but no greater than about 10 nm. Many insects can detect the ultraviolet
light that is commonly reflected from flowers. Although ultraviolet light is less
energetic than gamma- or X-rays, it is known to cause skin cancer particularly with
increased exposure.
X-ray waves
X-rays are produced when fast-moving electrons are fired into an
atom. The name is a result of scientists not knowing what they were
when they were first detected, hence the letter ‘X’. X-rays can pass
through body tissue and be detected by photographic film, and so
are used in medical diagnosis.
Gamma-ray waves
The highest energy, smallest wavelength radiation is the gamma ray, which is
produced within the nucleus of an atom. Gamma rays are one of the three types of
emissions that come from radioactive (unstable) atoms. Gamma rays are emitted in
nuclear fission bomb explosions. They are extremely penetrating and require dense
material to absorb them.
PHYSICS IN ACTION EXAMPLE:
94.7 is a radio station that broadcasts using radio waves of frequency 94.7 MHz.
Answer the following questions:
1.
How many times a second does an electron in the radio broadcasting antennae
move up and down the antennae?
2.
What is the wavelength of the radio signals sent out by this radio station?
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EXERCISE 7:
1.
What is EMR?
2.
Explain how EMR is produced.
3.1
3.2
List three different types of EMR and describe a use for each.
List two properties common to all forms of EMR.
4.
4.1
4.2
Light travels at 300 000 000 m/s in vacuum.
How fast do radio waves travel?
Calculate the wavelength of microwaves of frequency 3 × 1010 Hz.
4.3
4.4
4.5
[10-2 m]
Calculate the wavelength of ultraviolet radiation of frequency 1015 Hz.
[3 x 10-7 m]
Calculate the wavelength of the 80 MHz waves used for broadcasting on
VHF?
[3.75 m]
What is the frequency of the 1 500 m radio waves used on the Long Wave
Band?
[200 kHz]
5.
Our eyes respond to EMR with a
wavelength range from 780 to
390 nm. Each colour in the
spectrum has its own wavelength.
What is the frequency range
visible to the eye?
[385 THz – 769 THz]
6.
Explain why ultrasound is used to monitor the development of babies instead
of X-rays. Please describe the differences between the two types of waves and
give scientific reasons for your answer.
REFERENCES
1
Heinemann Physics 11, Fry et al, 2007
New Experiencing Physics “Waves, Sound, Light and Particles”, Len Victor 2007
3
Conceptual Physics, Paul Hewitt, 1998
4
Principles of Physics, Seventh Edition, M. Nelkon, Hart-Davis Educational
5
The Reader’s Digest Great Encyclopaedic Dictionary, Volume 3
6
PowerPoint presentation by Suzie Crossman
7
Hilton College Physical Science Notes by Trevor van Niekerk
8
Wikipedia
2