Correcting Units (Edexcel International A Level (IAL) Physics): Revision Note

Katie M

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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

Answer:

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 Content Creator

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.

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