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Physics 344
Foundations of 21
st
Century Physics:
Relativistic and Quantum Systems
Instructor:
Dr. Mark Haugan
Office:
PHYS 282
[email protected]
TA:
Dan Hartzler
Office:
PHYS 7
[email protected]
Grader:
Fan Chen
Office:
PHYS 222
[email protected]
Office Hours:
If you have questions, just email us to make an
appointment.
We enjoy talking about physics!
Reading: Sections 1.1 through 1.5 and Chapter 2 in Six Ideas that
Shaped Physics, Unit R.
Help Session: A schedule conflict is forcing us to shift the start and
finish times for the session by half an hour. For the rest of
the semester it will run from 2:00 – 4:00pm on Thursdays.
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View Full Document Inertial Coordinate Systems
When we predicted the relativistic velocity of an electron exiting a particle
accelerator we did so partly to emphasize the role that an inertial coordinate
system plays whenever we use fundamental principles to explain or predict
something.
When we considered how to measure a relativistic electron’s velocity we did so
partly to illustrate and emphasize that measuring the spacetime coordinates
which represent where and when something happens in an inertial coordinate
system is a bit trickier than you might have thought.
We developed a conceptual model of an inertial
reference frame as a lattice of rulers and
synchronized
clocks to deal with the subtle
problem of measuring the times at which
events at different locations occur.
x
y
z
When we select a location as an origin,
coordinate axes and an instant as a zero
of time we define an inertial coordinate
system that assigns a unique set of
spacetime coordinates
x
,
y
,
z
and
t
to every event.
Clock Synchronization and Simultaneity
One natural way to synchronize the clocks in
our model
inertial coordinate system is to
preset each one to an appropriate time and
to start them when they receive a flash of
light emitted by the clock at the origin.
If we set the clock at the origin to read
t
= 0 sec
and start it when the flash is emitted, we
must preset the clock at the location
represented by spatial coordinates
x
,
y
and
z
to the time
d/c
, where
is the clock’s distance from the origin,
for it to be properly synchronized by this process.
2
2
2
d
x
y
z
=
+
+
Notice that for our synchronization procedure to work it must be the case that
the speed of light in vacuum has the same unchanging value
c
for light
propagating in all directions away from the clock at the origin that emits the
synchronizing pulse.
x
y
z
Events are simultaneous when the synchronized clocks at their locations read
the same time when they occur.
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View Full Document So far, we have justified believing this to be true
by appealing to our welltested fundamental principles of electromagnetic
physics, Maxwell’s equations. They predict light propagates in just that way.
For the same synchronization procedure to work
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This note was uploaded on 12/09/2011 for the course PHYS 344 taught by Professor Garfinkel during the Fall '08 term at Purdue University.
 Fall '08
 Garfinkel
 Physics

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