SI Units

The mass of the International Prototype of the Kilogram (a cylinder of platinum-iridium metal) may have changed due to

• contamination of the cylinder

• changes in gravitational field

• expansion of the cylinder

The new standard of the kilogram uses an instrument called the

• mass balance

• Kibble balance

• electronic balance

The new standard metre is based on the

• speed of light in vacuum

• 10^-7 of the distance from the North Pole to the equator

• length of a wooden stick

Atomic clocks are based on the vibrations of a Caesium-133 atom because

• they can vibrate

• they are stable and easy to handle

• they are easily found

The ampere is based on

• the force between two long wires carrying the same current

• the current in a standard wire when a fixed voltage is connected across it

• the flow of electrons in a semi-conductor circuit

At zero Kelvin, all molecules would

• be in gaseous state

• form a crystal lattice

• have lost their energy of motion

Thermal imaging measures the

• intensity of electromagnetic radiation from objects

• difference in the temperature of various parts of the object

• hottest part of the object

The mole is based on

• the number of atoms in a typical avocado fruit

• the Avogadro constant which is the number of elementary entities (atoms, molecules etc)

• the Arigatou constant

The candela was based on gas flame standards but it was not ideal because

• not all countries have access to gas

• the standards varied from one device to another

• the device had poor safety standards

The candela is now defined based on the frequency of the green-yellow portion of the visible light spectrum because

• it is soothing to the eye

• it is in the middle portion of the spectrum

• the human eye sees this colour most intensely