What was the standard for the metre based on in 1960?
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The wavelength of orange-red light emitted by atoms of krypton.
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What was the standard for the metre based on in 1960?
The wavelength of orange-red light emitted by atoms of krypton.
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.
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.
What are the seven fundamental quantities?
Length, mass, time, temperature, electric current, luminous intensity, and amount of substance.
What is parallax?
The apparent change in position of an object due to a change in the position of the observer.
What is the angle subtended by points A and B at the position of a star?
AB/distance of the star from the Earth.
What is the relationship between radians and degrees?
1 radian = 180/π degrees, approximately 57.297°.
How should symbols for units be written?
They do not take plural form and should not contain full stops at the end.
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.
What is the SI unit for length?
Metre (m).
What is the speed of light in vacuum?
299792458 m/s.
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.
What is the closest star to Earth?
The Sun.
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).
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.
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.
What is the SI unit used to measure length or distance?
Metre (m).
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.
What is the correct way to express the unit of acceleration?
As m/s² or m s⁻², but not m/s/s.
What is the atomic mass unit (amu) defined in terms of?
The mass of a C-12 atom.
What is the SI unit of time?
The second (s).
What are the two supplementary units in addition to the seven fundamental units?
Plane angle (d8) and solid angle (dQ).
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.
What is an astronomical unit (AU)?
The mean distance between the center of the Earth and the center of the Sun.
What was the previous definition of a kilogram based on?
A specific piece of platinum-iridium alloy.
What is required for a measurement?
A comparison with a standard measuring unit that is internationally accepted.
How many fundamental quantities are there?
There are seven fundamental quantities.
What does SI stand for?
System International.
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.
What is the unit of solid angle measured in?
Steradians (sr).
What is the approximate wavelength of electrons in an electron microscope?
About 0.6 Å.
What is the angular diameter of a planet?
The angle subtended by the diameter of the planet at a single point on Earth.
What is the distance between two opposite points A and B along the Earth's orbit?
2 AU (Astronomical Units).
What method is used to make simultaneous observations of an astronomical object?
Selecting two distant points on the Earth.
How far is the next closest star from Earth?
4.29 light years.
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.
What is the new definition of a kilogram based on?
The magnitude of electric current.
What tools are used to measure very small distances, such as the size of atoms?
Electron microscope or tunneling electron microscope.
What are derived quantities?
Quantities that depend on some or all of the seven fundamental quantities.
How is the diameter of the Earth calculated using the angle subtended at the moon?
Diameter = angle subtended × distance to the moon.
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.
What is a parsec?
The distance from which one astronomical unit subtends an angle of one arcsecond.
What is physics primarily concerned with?
Physics is a quantitative science that measures various physical quantities during experiments.
What are fundamental quantities?
Physical quantities that do not depend on any other quantities for their measurements.
What is the SI unit of velocity?
Metres per second (m/s).
What is the SI unit for mass?
Kilogram (kg).
