178 Science and Technology
Light is a type of energy known as electromagnetic
radiation. It is given out by hot objects such as the
Sun, light bulbs, and. LASERS. When light hits
a surface, its energy can be absorbed (soaked up),
. REFLECTED, or deflected by. REFRACTION.
HOW DOES LIGHT TRAVEL?
Light travels as a wave. But unlike sound waves or
water waves, it does not need any matter or material
to carry its energy along. This means that light can
travel through a vacuum – a completely airless space.
(Sound, on the other hand, must travel through
a solid, a liquid, or a gas.) Nothing travels faster than
light energy. It speeds through the vacuum of space
at 300,000 km (186,400 miles) per second.WHAT MAKES SOME MATERIALS OPAQUE?
When light falls on a material, the energy in its
photons can affect the atoms in the material. In some
materials, such as metal, the atoms absorb some of the
photons so light does not pass through them. These
materials are opaque. In other materials, such as glass,
the atoms cannot absorb the photons and light passes
through them. These materials are transparent.WHAT ARE SHADOWS?
Light waves travel out from their source in straight
lines called rays. Rays do not curve around corners,
so when they hit an opaque object (one that does not
allow light to pass through it), they are blocked from
reaching the other side of that object. We see a dark
shadow in the area from which light is blocked.WHAT IS LIGHT?
Light is made up of little packets of energy called
photons. Most of these photons are produced when
the atoms in an object heat up. Heat “excites” the
electrons inside the atoms and they gain extra energy.
This extra energy is then released as a photon. The
hotter an object gets, the more photons it gives out.4 POLARIZING LIGHT
Bright sunlight reflected from the
road dazzles our eyes. One way of
cutting down the glare is to look
through a polarizing filter. Light
waves vibrate (shake) in all
directions. A polarizing filter lets
through light vibrating in only
one direction, blocking out the
rest and reducing glare.ENERGY-EFFICIENT LIGHT BULB 3
Compact fluorescent lamps (CFL) feature a spiralling
glass tube full of gases, which emit ultraviolet light
when electricity flows through them. This triggers a
phosphor coating on the tube to shine brightly.
A CFL is more energy efficient and lasts a lot longer
than standard incandescent bulbs.Light
The ballast sends electricity
through the tubeThe screw-in base allows the
bulb to fit securely in
the socketThe glass tube
is full of argon gas
and mercury vapour,
which gives off
ultraviolet radiation.
This makes the
phosphor coating
on the tube glowlight