2.1 – The units of energy and power

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Did you know that there only 7 base units as expressed by the International System of Units (SI)?

  • Length - meter (m)
  • Time - second (s)
  • Amount of substance - mole (mole)
  • Electric current - ampere (A)
  • Temperature - kelvin (K)
  • Luminous intensity - candela (cd)
  • Mass - kilogram (kg)

A value for each of these has come from seven constants that have been measured, such as the speed of light and the Planck constant.  https://www.nist.gov/pml/weights-and-measures/metric-si/si-units

But of course, there are many other useful units. Force, energy and power are used so commonly that they have their own SI units (and there are 19 other derived units too).

  • Force – newton (N)
  • Energy – joule (J)
  • Power – watt (W)

However, these derived units can be expressed using the base SI units

You can work out the base SI units for the newton by using the equation:

cap f equals m times a

one cap n equals one k times g multiplication one m solidus s squared

Therefore, one n times e times w times t times o times n  is the same as  one k times g m solidus s squared .

Task - units of joule

What are the base SI units for the joule?
A) k times g solidus s squared
B) k times g m s
C) k times g m solidus s cubed
D) k times g m squared solidus s squared

Task - units of power

The watt (the SI unit for power) can be written in several different ways. Which of the following are correct? 

(you can select more than one answer)

A)  cap n m solidus s
B)   cap j solidus s
C)  cap v times cap a
D)  k times g m squared solidus s cubed

Answers on the next page.

2 – Introduction: energy calculations

2.1b - The units of energy and power answers

Last modified: Sunday, 19 December 2021, 9:08 PM