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Exam Pack 2: RC ( Pendulum Clock)

This topic has 3 expert replies and 0 member replies
joealam1 Senior | Next Rank: 100 Posts Default Avatar
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Exam Pack 2: RC ( Pendulum Clock)

Post Tue Dec 06, 2016 6:09 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    The ultimate pendulum clock, indeed the ultimate mechanical clock of any kind, was invented by a British engineer, William Shortt. The first was installed in the Royal Observatory in Edinburgh in 1921. The Shortt clock had two pendulums, primary and secondary. The primary pendulum swung freely in a vacuum chamber. Its only job was to synchronize the swing of the secondary pendulum, which was housed in a neighboring cabinet and drove the time-indicating mechanism. Every 30 seconds the secondary pendulum sent an electrical signal to give a nudge to the primary pendulum. In return, via an elaborate electromechanical linkage, the primary pendulum ensured that the secondary pendulum never got out of step.

    Shortt clocks were standard provision in astronomical observatories of the 19205 and 19305, and are credited with keeping time to better than two milliseconds in a day. Many were on record as losing or gaining no more than one second in a year-a stability of one part in 30 million. The first indications of seasonal variations in the earth's rotation were gleaned by the use of Shortt clocks.

    In 1984 Pierre Boucheron carried out a study of a Shortt clock which had survived in the basement of the United States Naval Observatory since 1932. After replacing the electromechanical linkage with modern optical sensing equipment, he measured the Shortt clock's rate against the observatory's atomic clocks for a month. He found that it was stable to 200 microseconds a day over this period, equivalent to two to three parts in a billion. What is more, the data also revealed that the clock was responding to the slight tidal distortion of the earth due to the gravitational pull of the moon and the sun.

    In addition to causing the familiar ocean tides, both the sun and the moon raise tides in the solid body of the earth. The effect is to raise and lower the surface of the earth by about 30 centimeters. Since the acceleration due to gravity depends on distance from the center of the earth, this slight tidal movement affects the period of swing of a pendulum. In each case the cycle of the tides caused the clock to gain or lose up to 140 microseconds.


    Question 1. The passage most strongly suggests that its author would
    agree with which of the following statements about clocks?

    A) Before 1921 no one had designed a clock that used
    electricity to aid in its timekeeping functions.

    B) Atomic clocks depend on the operation of
    mechanisms that were invented by William Shortt
    and first used in the Shortt clock.

    C) No type of clock that keeps time more stably and
    accurately than a Shortt clock relies fundamentally on
    the operation of a pendulum.

    D) Subtle changes in the earth's rotation slightly reduce
    the accuracy of all clocks used in observatories after
    1921.

    E) At least some mechanical clocks that do not have
    pendulums are almost identical to Shortt clocks in
    their mode of operation.

    OA:C
    How can we infere C + it is too extreme " No Clock"

    Question 2. According to the passage, the use of Shortt clocks
    led to the discovery that

    A) optical sensing equipment can be used effectively in
    time-keeping systems

    B) atomic clocks can be used in place of pendulum
    clocks in observatories

    C) tides occur in solid ground as well as in oceans

    D) the earth's rotation varies from one time of year to another

    E) pendulums can be synchronized with one another electronically

    OA:D

    Question 3. The passage most strongly suggests that the study
    described in the third paragraph would not have been possible in the absence of

    A) accurate information regarding the times at which
    high and low ocean tides occurred at various locations during 1984

    B) comparative data regarding the use of Shortt clocks in observatories between 1921 and 1932

    C) a non-Shortt clock that was known to keep time extremely precisely and reliably

    D) an Innovative electric-power source that was not available in the 1920s and 1930s

    E) optical data-transmission devices to communicate between the U.S. Naval Observatory and other
    research facilities

    OA:C

    Question 4. The passage most strongly suggests that which of the
    following is true of the chamber in which a Shortt clock's
    primary pendulum was housed?

    A) It contained elaborate mechanisms that were
    attached to, and moved by, the pendulum.

    B) It was firmly sealed during normal operation of the
    clock.

    C) It was at least partly transparent so as to allow for
    certain types of visual data output.

    D) It housed both the primary pendulum and another
    pendulum.

    E) It contained a transmitter that was activated at
    irregular intervals to send a signal to the secondary
    pendulum.

    OA:B

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    Post Mon Jan 09, 2017 5:34 pm
    Quote:
    The ultimate pendulum clock, indeed the ultimate mechanical clock of any kind, was invented by a British engineer, William Shortt. The first was installed in the Royal Observatory in Edinburgh in 1921. The Shortt clock had two pendulums, primary and secondary. The primary pendulum swung freely in a vacuum chamber. Its only job was to synchronize the swing of the secondary pendulum, which was housed in a neighboring cabinet and drove the time-indicating mechanism. Every 30 seconds the secondary pendulum sent an electrical signal to give a nudge to the primary pendulum. In return, via an elaborate electromechanical linkage, the primary pendulum ensured that the secondary pendulum never got out of step.

    Shortt clocks were standard provision in astronomical observatories of the 19205 and 19305, and are credited with keeping time to better than two milliseconds in a day. Many were on record as losing or gaining no more than one second in a year-a stability of one part in 30 million. The first indications of seasonal variations in the earth's rotation were gleaned by the use of Shortt clocks.

    In 1984 Pierre Boucheron carried out a study of a Shortt clock which had survived in the basement of the United States Naval Observatory since 1932. After replacing the electromechanical linkage with modern optical sensing equipment, he measured the Shortt clock's rate against the observatory's atomic clocks for a month. He found that it was stable to 200 microseconds a day over this period, equivalent to two to three parts in a billion. What is more, the data also revealed that the clock was responding to the slight tidal distortion of the earth due to the gravitational pull of the moon and the sun.

    In addition to causing the familiar ocean tides, both the sun and the moon raise tides in the solid body of the earth. The effect is to raise and lower the surface of the earth by about 30 centimeters. Since the acceleration due to gravity depends on distance from the center of the earth, this slight tidal movement affects the period of swing of a pendulum. In each case the cycle of the tides caused the clock to gain or lose up to 140 microseconds.


    Question 1. The passage most strongly suggests that its author would
    agree with which of the following statements about clocks?

    A) Before 1921 no one had designed a clock that used
    electricity to aid in its timekeeping functions.

    B) Atomic clocks depend on the operation of
    mechanisms that were invented by William Shortt
    and first used in the Shortt clock.

    C) No type of clock that keeps time more stably and
    accurately than a Shortt clock relies fundamentally on
    the operation of a pendulum.

    D) Subtle changes in the earth's rotation slightly reduce
    the accuracy of all clocks used in observatories after
    1921.

    E) At least some mechanical clocks that do not have
    pendulums are almost identical to Shortt clocks in
    their mode of operation.

    OA:C
    How can we infere C + it is too extreme " No Clock"
    In the second paragraph, we get the following quote about Shortt clocks: Many were on record as losing or gaining no more than one second in a year-a stability of one part in 30 million.

    So we know that these clocks, which rely on the operation of a pendulum, are extraordinarily accurate.

    In the next paragraph, in which the Shortt clocks are compared to atomic clocks, we see that the Shortt clocks are nearly as accurate as the atomic clocks, and we also get this: the data also revealed that the clock was responding to the slight tidal distortion of the earth due to the gravitational pull of the moon and the sun.

    So there's almost no difference in accuracy between the Shortt clocks and the atomic clocks (atomic clocks, presumably, being the standard for accuracy) and what difference exists is a function of tidal distortion.

    In the last paragraph, we get this line: this slight tidal movement affects the period of swing of a pendulum.

    Taken together we know that there's almost nothing more accurate than a Shortt clock; the Shortt clock only falls short of an atomic clock because the tide very slightly distorts its pendulum swing. Because any pendulum clock would suffer from this same distortion, it's reasonable to conclude that clock more accurate than a Shortt clock won't operate via a pendulum. So the answer is C

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    Post Mon Jan 09, 2017 5:36 pm
    Quote:
    Question 2. According to the passage, the use of Shortt clocks
    led to the discovery that

    A) optical sensing equipment can be used effectively in
    time-keeping systems

    B) atomic clocks can be used in place of pendulum
    clocks in observatories

    C) tides occur in solid ground as well as in oceans

    D) the earth's rotation varies from one time of year to another

    E) pendulums can be synchronized with one another electronically
    We can pull this one right from the last line of paragraph 2: The first indications of seasonal variations in the earth's rotation were gleaned by the use of Shortt clocks.

    D is a paraphrase of this idea.

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    Post Mon Jan 09, 2017 5:38 pm
    Quote:
    Question 3. The passage most strongly suggests that the study
    described in the third paragraph would not have been possible in the absence of

    A) accurate information regarding the times at which
    high and low ocean tides occurred at various locations during 1984

    B) comparative data regarding the use of Shortt clocks in observatories between 1921 and 1932

    C) a non-Shortt clock that was known to keep time extremely precisely and reliably

    D) an Innovative electric-power source that was not available in the 1920s and 1930s

    E) optical data-transmission devices to communicate between the U.S. Naval Observatory and other
    research facilities
    The key line: he measured the Shortt clock's rate against the observatory's atomic clocks for a month
    So he's assessing the accuracy of the Shortt clock by comparing it to an accurate non-Shortt clock. The answer is C

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