Chapter 27 Flashcards
(85 cards)
How long has light been studied?
For thousands of years.
What did Greek philosophers think of light?
That it consisted of tiny particles which could enter the eye to create the sensation of vision
What did Socrates and Plato think?
That vision resulted from streamers or filaments emitted by the eye making contact with an object.
Up until _________, most philosophers and scientists thought that light consisted of particles .
Newton
Who taught that light traveled in waves.
Empedocles and Christian Huygens
How was the particle theory supported?
By the fact that light seemed to move in straight lines instead of spreading out as waves do.
What evidence did Huygens provide?
That under some circumstances light does spread out (diffraction)
Who published a theory in 1905 explaning the photoelectric effect?
Einstein
Light consists of …
Photons
What are photons?
Massless bundles of concentrated electromagnetic energy.
Scientists now agree that light has a _______nature, part __________and part __________.
dual; particle; wave
It was not known whether light travels instantaneously or with finite speed until…
the late 1600s
Who tried to measure the time a light beam takes to travel to a distant miror and back?
Galileo
Why couldn’t Galileo measure the time a light beam takes to travel to a distant miror and back?
The time was so short that he couldn’t begin to measure it.
What happened to the people who tried to measure the time a light beam takes to travel to a distant miror and back?
They succeeded in measuring their own reaction times
Who supplied the first demonstration that light travels at a finite speed?f
Danism astronomer Olaus Roemer, 1675
What did Roemer do first?
He made very careful measurements of the periods of Jupiter’s moons.
What is the innermost moon of jupiter called?
Io
How long does it take Io to revolve around Jupiter?
42.5 hours
How could Roemer be sure that his measurements were accurate?
Bc Io disappears periodically into Jupiters shadow
What irregularities did Roemer find?
While Earth wasmoving away from Jupiter, from position B to C, the measured periods of Io were all somewhat longer than average. When Earth was moving toward Jupiter, from E to F, the measured periods were shorter than average.
What did Roemer estimate about the cumulative discrepancy between A and D?
The cumulative discrepancy between A and D amounted to about 22 minutes, when Earth was at position D, Io would pass into Jupiter’s shadow 22 minutes late, compared with observations at position A.
What did Christian Huygens interpret about the discrepancy?
When Earth was farther away from Jupiter, it was the light that was late, not the moon.
Io passed into Jupiter’s _________at the predicted time, but the _______carrying the message did not reach Roemer until it had traveled the extra distance across the diamter of _________ ________.
shadow; light; Earth’s orbit
