1. The Visible Spectrum
When white light passes through a prism, it is separated into
its constituent colors: the red, orange, yellow, green, blue, indigo
and violet.
These colors do not distinctly separate but they continuously
change from red to violet.
Red color has the longest wavelength from among these
colors and violet has the shortest.
2.
3. Table 3 shows the wavelengths of the different colors that
constitute the white light.
4. Visible light has several applications, including:
• Fiber optic communications, where coded pulses of light travel
through glass fibers from a source to a receiver.
• Photography and illumination.
• Electronic devices.
• Sunlight, which is a prominent example of visible light in real
life.
• Light bulbs, which are a common light source used in
households.
• Photosynthesis
5. Activity 6
Screen the UV out
Objectives:
• Block UV rays of the sun.
• Discover the effects of UV rays.
6. Materials:
• Ziploc snack bag
• newspaper
• sunscreen/sunblock
• black construction paper
• permanent marker
Procedure:
1. Cut a piece of newspaper to fit snugly inside a Ziploc snack bag.
2. Outside the snack bag, draw two lines with a marker dividing the
bag into three equal parts from the top of the bag to the bottom.
3. Apply a thin coat of sunscreen in the leftmost part.
7. 4. Cover the middle part with black construction paper.
5. The right part should be left fully exposed.
6. Place the snack bags in a place fully exposed to sunlight.
7. Recover the snack bags in the afternoon.
8. Ultraviolet Radiation
Ultraviolet radiation lies just beyond the violet end of the
visible spectrum.
Ultraviolet waves have shorter wavelengths than the visible
light and carry more energy.
9. Types of UV light
UV light or UV ray is classified into three components:
ultraviolet A (UVA), ultraviolet B (UVB), and ultraviolet C (UVC).
Following is the table explaining the characteristics of these
components:
Ultraviolet A (UVA):
Most of the UV (98.7%) that reaches us on the earth’s surface is of
type UVA and is affected by the ozone
• Fading of paints and dyes.
• UVA causes early aging of the skin.
• UVA causes skin cancer called melanoma.
10. Ultraviolet B (UVB):
1.3% of the UV reaches the earth’s surface and is highly affected
by ozone.
• These rays are responsible for sunburn and tan.
• To produce vitamin D, 270-300 nm wavelengths are stimulated.
Ultraviolet C (UVC):
UVC rays do not reach the earth’s surface as most of them are
absorbed by the atmospheric nitrogen, oxygen, and ozone, and
the rest are scattered.
• UVC causes lesions on the skin.
11. Some Uses of UV Radiation
The sun is our main source of ultraviolet radiation but there
are also artificial sources of UV light.
Ultraviolet radiation in UV lamps are used by banks to check
the signature on a passbook. The signature is marked on
the passbook with fluorescent ink. It becomes visible when viewed
under an ultraviolet lamp. These lamps are also used to identify
fake banknotes.
Ultraviolet radiation is also used in sterilizing water from
drinking fountains. Some washing powder also contains fluorescent
chemicals which glow in sunlight. This makes your shirt look whiter
than white in daylight.
12. Ultraviolet radiation in sunlight produces vitamin D in the skin
and gives us tanning effect. But since UV rays have high energy, it
could be harmful to some extent. It could burn the skin and hurt
our eyes.
Overexposure to UV radiation may cause skin cancer. Suntan
or sunscreen lotions serve as filters to protect the body from
ultraviolet radiation.
