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Unit 9: Light Page 16
conductive. More on this in Unit charge, which can wreck havoc on
10). its internal computer systems.
When Einstein aimed a red light at A surprising find was back in the
the metal sheet, nothing 1960s, when scientists discovered
happened. Even when he cranked that moon dust levitated through
the intensity (brightness) of the the photoelectric effect. Sunlight
red light, still nothing happened. hit the lunar dust, which became
So it was the energy of the light (slightly) electrically charged, and
(wavelength), not the number of the dust would then lift up off the
photons (intensity) that made the surface in thin, thread-like
electrons eject from the plate. This fountains of particles up ¾ of a
is called the ‘photoelectric effect’. mile high.
Can you imagine what happens if
we aim a UV light (which has even So what is light?
more energy than blue light) at the
plate? There is no contradiction between
light acting like a particle or a
This photoelectric effect is used by wave. You need both to describe all
all sorts of things today, including the ways that light behaves. Note
solar cells, electronic components, that you can’t have both at the
older types of television screens, same time, however.
video camera detectors, and night-
vision goggles. What ultimately decides which light
decides to do? You.
If you do an experiment that
involves wave aspects of light, like
shining a laser through slits, you’ll
see an interference pattern. If you
set up an experiment that detects
light as a particle, like the
photoelectric effect, you’ll find that
light acts like a particle.
This photoelectric effect also Does this seem absurd to you? If it
causes the outer shell of orbiting does, you’re not alone. Most
spacecraft to develop an electric scientists feel the same way!
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