Correcting Units (Edexcel International A Level Physics)

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Katie M

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Correcting Units

  • In Physics, a value without its appropriate unit doesn't really mean anything
    • For example, 5 mm or 5 km are very different measurements
  • Some common units in A-level Physics are:

Common Units Table

Common Units Table

  • Sometimes practical questions require identifying units that are incorrect
  • Learning the appropriate unit for each physical quantity in A-level physics is extremely important
  • Sometimes the unit can be derived from an equation for that quantity
    • For example, the units of the resistivity ρ can be considered from its equation

ρ = fraction numerator R A over denominator L end fraction

  • Where:
    • R = resistance (Ω)
    • A = area (m2)
    • L = length (m)
  • Therefore:

[ρ] = fraction numerator left square bracket R right square bracket left square bracket A right square bracket over denominator left square bracket L right square bracket end fraction =  fraction numerator capital omega m squared over denominator m end fraction = Ωm

  • Common units for measurements are:
    • Length = m 
    • Area = m2
    • Volume = m3

Worked example

Correct the following incorrect units:

  1. Magnetic Flux Density = 2 Webers
  2. Electromotive Force = 7.8 N
  3. Capacitance = 0.3 µC
  4. Stress = 600 m2

The correct units are:

    1. Magnetic Flux Density = 2 T (Tesla)
    2. Electromotive Force = 7.8 V (Volts)
    3. Capacitance = 0.3 µF (Micro-farads)
    4. Stress = 600 Pa (Pascals)

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Katie M

Author: Katie M

Expertise: Physics

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.