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Introduction to Physics and Measurement
What is physics primarily concerned with?
Physics is a quantitative science that measures various physical quantities during experiments.
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Fundamental Quantities and Units
What is required for a measurement?
A comparison with a standard measuring unit that is internationally accepted.
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Fundamental Quantities and Units
What are fundamental quantities?
Physical quantities that do not depend on any other quantities for their measurements.
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Fundamental Quantities and Units
How many fundamental quantities are there?
There are seven fundamental quantities.
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Fundamental Quantities and Units
What are the seven fundamental quantities?
Length, mass, time, temperature, electric current, luminous intensity, and amount of substance.
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Derived Quantities and Units
What are derived quantities?
Quantities that depend on some or all of the seven fundamental quantities.
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Measurement of Length and Distance
What was the standard for the metre based on in 1960?
The wavelength of orange-red light emitted by atoms of krypton.
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Fundamental Quantities and Units
What is the definition of solid angle (dQ)?
The area of a portion of the surface of a sphere to the square of the radius of the sphere.
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Parallax Method for Measuring Distances
Why can't the two eyes method be used for measuring distances to planets?
Because the distances of planets from the Earth are very large.
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Parallax Method for Measuring Distances
What is parallax?
The apparent change in position of an object due to a change in the position of the observer.
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Measurement of Large Distances to Stars
What is the angle subtended by points A and B at the position of a star?
AB/distance of the star from the Earth.
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Fundamental Quantities and Units
What is the relationship between radians and degrees?
1 radian = 180/π degrees, approximately 57.297°.
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Systems of Units: CGS, MKS, FPS, and SI
How should symbols for units be written?
They do not take plural form and should not contain full stops at the end.
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Measurement of Time and the Second
What was used as a reference for the duration of one mean solar day?
The average time interval from one noon to the next noon.
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Systems of Units: CGS, MKS, FPS, and SI
What is the convention for writing the full name of a unit?
It should always start with a small letter, even if named after a person.
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Measurement of Small Distances: Atomic Scale
What is the unit used for measuring small distances in the SI system?
Fermi (1 fermi = 10^-15 m) and Angstrom (1 Å = 10^-10 m).
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Parallax Method for Measuring Distances
What is the parallax angle in the context of measuring distances to a distant planet?
The angle LASB between the two directions along which the planet is viewed from two points.
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Systems of Units: CGS, MKS, FPS, and SI
What is the significance of prefix symbols in units?
They are used before the symbol of the unit to create a new symbol that can be raised to a power of 10.
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Fundamental Quantities and Units
How is the plane angle (d8) defined?
As the ratio of the length of an arc of a circle to the radius of the circle.
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Systems of Units: CGS, MKS, FPS, and SI
What is the correct way to express the unit of acceleration?
As m/s² or m s⁻², but not m/s/s.
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Fundamental Quantities and Units
What are the two supplementary units in addition to the seven fundamental units?
Plane angle (d8) and solid angle (dQ).
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Parallax Method for Measuring Distances
How can the distance of an object be determined using parallax?
By measuring the parallax angle and knowing the distance between the observer's eyes.
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Measurement of Large Distances to Stars
What is an astronomical unit (AU)?
The mean distance between the center of the Earth and the center of the Sun.
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Measurement of Mass and the Kilogram Definition
What was the previous definition of a kilogram based on?
A specific piece of platinum-iridium alloy.
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Measurement of Length and Distance
How is a metre defined as of 1983?
As the length of the path travelled by light in vacuum during a time interval of 1/299792458 second.
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Measurement of the Size of a Planet or Star
What is the angular diameter of a planet?
The angle subtended by the diameter of the planet at a single point on Earth.
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Measurement of Large Distances to Stars
What is the distance between two opposite points A and B along the Earth's orbit?
2 AU (Astronomical Units).
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Parallax Method for Measuring Distances
What method is used to make simultaneous observations of an astronomical object?
Selecting two distant points on the Earth.
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Parallax Method for Measuring Distances
What is the relationship between the parallax angle (θ) and the distance (D) to a distant planet?
θ is approximately equal to AB/D, where AB is the length of the base and D is the radius.
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Measurement of Mass and the Kilogram Definition
What is the new definition of a kilogram based on?
The magnitude of electric current.
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Measurement of Small Distances: Atomic Scale
What tools are used to measure very small distances, such as the size of atoms?
Electron microscope or tunneling electron microscope.
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Measurement of Large Distances to Stars
How is the diameter of the Earth calculated using the angle subtended at the moon?
Diameter = angle subtended × distance to the moon.
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Measurement of the Size of a Planet or Star
How can the diameter of a planet be calculated?
Using the formula d = aD, where d is the diameter, a is the angular diameter, and D is the distance to the planet.
p.4
Measurement of Large Distances to Stars
What is a parsec?
The distance from which one astronomical unit subtends an angle of one arcsecond.
