Correcting Units (Edexcel IAL Physics)

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

• 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 = $\frac{RA}{L}$

• Where:

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

• Therefore:

[ρ] = $\frac{[ R ] [ A ]}{[ L ]}$ = $\frac{Ωm^{2}}{m}$ = 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)