Elenco LIGHT - Manual (Page 13)

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Light in Our World
The Spectrum of Light
The light our eyes see is only part of what is around us. Visible light,
infrared light, radio waves (including TV broadcasting and cell phones),
microwaves, and x-rays are all forms of electromagnetic radiation. They
are actually changing electric and magnetic fields. This radiation travels
like waves in water, spreading out from where it was created. These
waves all travel at the speed of light, but some are longer (higher
wavelength) and some repeat faster (higher frequency). Together they
are called the electromagnetic spectrum:
The visible colors (red, orange, yellow, green, blue, and violet) have
different wavelengths. In the right conditions white light from the sun can
be separated according to wavelength, producing a rainbow of color. This
happens with an actual rainbow, and with prismatic film.
Why is the sky blue? Some sunlight is scattered by tiny particles in the
earth’s atmosphere. The shorter wavelength blue light is scattered more
than the other colors, so the sky appears blue. At sunrise or sunset,
longer wavelength
colors like red or
yellow are more
visible in the sky,
because sunlight
passes through more
of the atmosphere
before reaching your
eyes. In space, the
sky always appears
black because there
is no atmosphere or
scattering effect.
Infrared
Infrared light is invisible light given off by
anything warm. Infrared is used in remote
controls to control TVs and appliances.
Infrared is invisible, so it doesn’t disrupt
your view of the TV. Infrared doesn’t go
through walls, so it doesn’t interfere with
devices in other rooms.
The remote control sends a stream of
infrared light pulses to the TV, encoded with
the desired commands. The infrared light is
created using an infrared light emitting
diode (LED). Infrared detectors convert the
received light to electric current, and
decode the commands. The detectors are
tuned to focus on the infrared light, and
ignore visible light. This set contains an
infrared detector (U24), which can be
activated by a TV remote control; see
projects 41 and 42 for examples.
Infrared has other uses such as night vision
devices help to see people and animals in
the dark, by looking at the heat they give off
as infrared light. You probably saw this in the
movies.
Glow-in-the-dark
Some materials can absorb light, store it for a while, and slowly release
it back out. “Glow-in-the-dark” materials can be “charged” by bright light,
then will slowly emit light and “glow” for a while in a dark room. The glow
fan blade in this set has a glow powder mixed in the plastic.
It’s like a slow, delayed reflection of the light.
Sound
Sound, like light, spreads out like waves from where it was made. Sound
is variations in air pressure. You “hear” sound when your ears feel these
air pressure variations. Sound has much longer wavelength than light,
which enables sound to travel around corners. Sound can also be
thought of as a wave of vibration, and can travel through water and solid
objects. Sound travels about 1,000 feet per second in air, and about
5,000 feet per second in water.