expressing quantities and SI units

• How many base units are there in the SI system?

  Six base units
• What are the SI Base Units used for?

  To derive other common units
• What is the unit for force in the SI system?

  Newtons, N
• What is the unit for energy in the SI system?

  Joules, J
• What is the unit for pressure in the SI system?

  Pascals, Pa
• Why is it important to remember units in exam answers?

  Marks may be awarded for correct units
• What is the diameter of an atom approximately?

  About $10^{-10} \text{ m}$
• How many powers of ten separate the diameter of an atom and the width of a galaxy?

  31 powers of ten
• What are the two categories of powers of ten?

  Multiples and sub-multiples
• How do you convert $12 \text{ GPa}$ to Pascals?


  $12 \times 10^9 \text{ Pa}$
• How do you convert $5 \text{ kN}$ to Newtons?


  $5 \times 10^3 \text{ N}$
• How do you convert $0.1 \text{ μA}$ to Amperes?


  $1 \times 10^{-7} \text{ A}$
• How do you convert $7 \text{ nC}$ to Coulombs?


  $7 \times 10^{-9} \text{ C}$
• Why is it important to be familiar with powers of ten?

  Common exam mistakes occur with prefixes
• What is the conversion factor from hours to seconds?

  1 hour = 3600 seconds
• How do you convert hours to seconds?

  Multiply by 3600
• How do you convert seconds to hours?

  Divide by 3600
• What is the relationship between Kelvin and degrees Celsius?

  0 K = -273.15 ºC
• How do you convert Kelvin to Celsius?

  Subtract 273.15
• How do you convert Celsius to Kelvin?

  Add 273.15
• If a cyclist takes 3.5 hours, how many seconds is that?

  12,600 seconds
• What are significant figures?

  Digits contributing to the value of a number
• How many significant figures does the number 123 have?

  Three significant figures
• How many significant figures does the number 1.78 have?

  Three significant figures
• Are zeros between significant digits considered significant?

  Yes, they are significant
• How many significant figures does the number 10003 have?

  Five significant figures
• How many significant figures does the number 1.006 have?

  Four significant figures
• Are trailing zeros in the decimal portion significant?

  Yes, they are significant
• How many significant figures does the number 0.183 have?

  Three significant figures
• How many significant figures does the number 1390 have?

  Three significant figures
• How many significant figures does the number 1.40 have?

  Three significant figures
• How many significant figures does the number 0.012 have?

  Two significant figures
• How many significant figures does the number 1.9000 have?

  Five significant figures
• What is the procedure for rounding to significant figures?

  Round based on the next digit's value
• How is standard form written?

  As $a \times 10^n$
• What does 'a' represent in standard form?

  A number between 1 and 10
• What does 'n' represent in standard form?

  How many times a is multiplied/divided by 10
• How do you write $300,000,000$ in standard form?


  $3 \times 10^8$
• How do you write $0.00002$ in standard form?


  $2 \times 10^{-5}$
• How do you round $5.18 \times 10^6$ to 2 significant figures?


  $5.2 \times 10^6$