Understanding Base Quantities and Units (GCHSS)

What is the SI base unit for length?

• centimetre

• millimetre

• kilometre

• metre

Answer explanation

The SI base unit for length is the metre. It is the standard unit used in the International System of Units (SI) to measure length, making it the correct choice among the options provided.

Which physical quantity is measured in kilograms.

• Density

• Mass

• Weight

• Volume

Answer explanation

Mass is the physical quantity measured in kilograms, representing the amount of matter in an object. Density is mass per unit volume, weight is the force due to gravity on mass, and volume measures space occupied.

What is the SI base unit for time?

• minute

• hour

• second

• day

Answer explanation

The SI base unit for time is the second. It is the standard unit used in scientific measurements, while minutes, hours, and days are derived units based on the second.

Choose ALL the DERIVED units

• Newton N

• Joule J

• kilogram kg

• Ampere A

Answer explanation

Derived units are formed from base units. Newton (N) is derived from kg·m/s², and Joule (J) is derived from N·m. Kilogram (kg) and Ampere (A) are base units, not derived.

Choose ALL the BASE units

• Mole (mol)

• Second (s)

• Gram (g)

• Centimetre (cm)

Answer explanation

The mole (mol) and second (s) are both base units in the International System of Units (SI). The gram (g) is a derived unit of mass, and the centimetre (cm) is a derived unit of length, thus not base units.

The SI base unit for electric current is:

• Ampere

• Watt

• Ohm

• Volt

Answer explanation

The SI base unit for electric current is the Ampere, often abbreviated as 'A'. It measures the flow of electric charge, distinguishing it from other units like Watt (power), Ohm (resistance), and Volt (voltage).

Which group of three physical quantities are all basic quantities?

• Force, mass, and accelerataion

• Heat, mass, and temperature

• Mass, length, and time

• Density, mass, and volume

Answer explanation

The correct choice is 'Mass, length, and time' as these are fundamental physical quantities in the International System of Units (SI). Other options include derived quantities or combinations of basic quantities.

What is the derived unit for force in the SI system?

• Watt (W)

• Joule (J)

• Pascal (Pa)

• Newton (N)

Answer explanation

The derived unit for force in the SI system is the Newton (N). It is defined as the force required to accelerate a one-kilogram mass by one meter per second squared, making it the correct choice.

What is the SI base unit for temperature?

• Kelvin

• Fahrenheit

• Celsius

• Centrigrade

Answer explanation

The SI base unit for temperature is the Kelvin. Unlike Fahrenheit and Celsius, which are based on arbitrary scales, Kelvin is an absolute scale starting at absolute zero, making it the standard unit in scientific contexts.

The 'mole' is the unit of which quantity?

• Amount of substance

• Mass

• Temperature

• Volume

Answer explanation

The 'mole' is the SI unit for the amount of substance, which quantifies the number of entities (atoms, molecules, etc.) in a sample. It is not a unit for mass, temperature, or volume.