Question

State the basic SI unit for each of the following physical quantities. (a) length (b) mass (c) volume (d) time (e) temperature (f) heat energy

Short answer

(a) meter, (b) kilogram, (c) cubic meter, (d) second, (e) kelvin, (f) joule.

Step-by-step solution

Understanding the SI System

The International System of Units (SI) is the standard metric system used globally for scientific measurements. It consists of seven base units which correspond to a set of fundamental physical quantities.

Identifying the Unit for Length

The basic SI unit for length is the meter, denoted as 'm'.

Identifying the Unit for Mass

The basic SI unit for mass is the kilogram, denoted as 'kg'.

Identifying the Unit for Volume

Volume is not a base SI unit, but the SI unit for volume is derived from the meter; it is the cubic meter, denoted as 'm³'.

Identifying the Unit for Time

The basic SI unit for time is the second, denoted as 's'.

Identifying the Unit for Temperature

The basic SI unit for temperature is the kelvin, denoted as 'K'.

Identifying the Unit for Heat Energy

Heat energy is commonly measured in joules, which is the derived SI unit denoted as 'J'.

Key concepts

Meter

The meter is the fundamental unit of length in the International System of Units (SI). It is denoted by the symbol 'm'. The meter was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. Over time, the definition of a meter has been refined. Today, it is defined by the distance light travels in a vacuum in 1/299,792,458 of a second. This provides a precise and consistent standard for scientific measurements.

• The meter is used in various scenarios, from measuring small objects to large distances.
• Common multiples and sub-multiples include centimeters (cm), kilometers (km), and millimeters (mm).

This unit helps scientists and engineers across the world communicate effectively with a standard set of measurement.

Kilogram

The kilogram is the base unit of mass in the SI system and is represented by the symbol 'kg'. One kilogram was historically defined using the mass of the International Prototype of the Kilogram, a cylinder made of platinum-iridium. However, in 2019, its definition was refined to be based on fundamental physical constants: it is now defined using the Planck constant.

• The kilogram is crucial in measuring mass in everyday life and scientific research.
• It connects the world of classical mechanics with the quantum realm by its current definition.

Multiples like grams (g) are also commonly used, where 1 kg equals 1000 grams, facilitating smaller-scale measurements if necessary.

Kelvin

Kelvin is the SI base unit of temperature, symbolized as 'K'. Distinct from other temperature scales like Celsius or Fahrenheit, Kelvin starts at absolute zero, the theoretical point where molecular motion ceases. The Kelvin scale provides an absolute measure of temperature.

• 0 Kelvin (or 0 K) is equivalent to -273.15 degrees Celsius.
• Kelvin is particularly used in scientific contexts, especially in physics and chemistry, where temperature needs precise quantification.

Using Kelvin simplifies computations since it relates directly to energy measurements through physical laws.

Joule

The joule, pronounced 'jool', is the derived SI unit of energy, denoted as 'J'. A joule is defined as the work done when a force of one newton is applied over a distance of one meter. It is also the energy transferred when consuming power of one watt for one second.

• The conversion relates to many everyday contexts; for example, 1 calorie is equivalent to approximately 4.184 joules.
• Joules can measure varied forms of energy, including mechanical, electrical, and heat.

This unit enables clear energy transfer and consumption measurement and provides consistency across physics, engineering, and many other fields.