CAIE A-Level Physics Algebra, Models and Dimensional Consistency

Practise rearranging linked physics equations, substituting consistent units and checking dimensions, percentages, symbols and quadratic solutions when the model requires them.

Exam points

change the subject of a physical equation and substitute values with consistent units
derive or check SI base units and dimensions of a quantity from a formula
rearrange simple physical relationships and interpret the resulting symbols

[Maximum number: 2]

The electric field strength E at a distance x from an isolated point charge Q is given by the equation

E=\frac{Q}{x^{2} b}

where b is a constant.

Use the units for E given in (b)(i) to determine the SI base units of b.

SI base units of b

$\begin{aligned} b =Q / X^{2} E =\mathrm{As} / \mathrm{m}^{2} \mathrm{kgmA}^{-1} \mathrm{~s}^{-3} \end{aligned}$

C1

$=\mathrm{A}^{2} \mathrm{~s}^{4} \mathrm{~kg}^{-1} \mathrm{~m}^{-3}$

A1

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M.2-Algebra, models, units and dimensional consistency question 1