IS LIGHT A MATTER?
It would seem that photons would
be matter whereas the waves wouldn't.
It turns out that for both
theories light isn't matter. A photon is
not matter because it has no mass. This
is different from matter such as
electrons and neutrons which have
masses.
Light is a particle-Isaac
Newton
Light is an
Electromagnetic WaveFresnel, Young and
Maxwell
Light is actually made up
of tiny packets of energy Einstein
Describe how Galileo
and Roemer
contributed to the
eventual acceptance of
the view that the speed
of light is finite
Galileo
It was generally taken for granted
that light-speed was infinite until
the astronomer Galileo in the early
1600's claimed that it was finite.
Distant lanterns with shutters
His conclusion was that light-speed
was too fast to be measured by
that experiment.
Ole
Romer
The first true measurement of the speed of light came
in 1676 by a fellow named Ole Roemer (Rømer). Roemer
was observing Jupiter's moon Io, the innermost of the
Galilean satellites.
 Io suddenly disappears when it moves into Jupiter's
shadow, and it suddenly reappears when it moves out
of Jupiter's shadow
Predicting the times at which Io would be observed to
emerge from Jupiter's shadow
Roemer calculated that it would take light about 22
minutes to cross the diameter of Earth's orbit
Gives a speed of light of about 210,000 kilometers per
second
About 30% lower than the modern value for the speed
http://curious.astro.cornell.edu/a
bout-us/148-people-inastronomy/history-ofastronomy/general-questions/993who-first-measured-the-speed-oflight-intermediate
http://www.speedlight.info/measure/speed_of_light
_history.htm
http://galileoandeinstein.physics.
virginia.edu/lectures/spedlite.htm
l
Heinrich
Hertz
Describe How
Hertz Produced
Radio Pulses
In November 1886 Hertz put together his spark-gap transmitter, which he
hoped would transmit electromagnetic waves.
Hertz’s spark-gap
transmitter. At the ends are
two hollow zinc spheres of
diameter 30 cm which are 3
m apart. These act as
capacitors. 2 mm thick
copper wire is run from the
spheres into the middle,
where there is a spark-gap.
Today we would describe
this oscillator as a half-wave
dipole antenna.
 For his receiver he used a length of copper wire in the
shape of a rectangle whose dimensions were 120 cm by 80
cm. The wire had its own spark-gap.
 Hertz applied high voltage a.c. electricity across the
central spark-gap of the transmitter, creating sparks.
 The sparks caused violent pulses of electric current within
the copper wires leading out to the zinc spheres.
 As Maxwell had predicted, the oscillating electric charges
produced electromagnetic waves – radio waves – which
spread out at the speed of light through the air around
the wire.
 Hertz detected the waves with his copper wire receiver –
sparks jumped across its spark gap, even though it was as
far as 1.5 meters away from the transmitter. These sparks
were caused by the arrival of electromagnetic waves from
the transmitter generating violent electrical vibrations in
the receiver.