OCR A-Level Physics/Equation Sheet

Equations, constants, and other useful data. Equations and constants are given in the formulae booklet unless stated otherwise.

AS Formulae

${\text{efficiency}}={\frac {\text{useful energy output}}{\text{total energy input}}}\times 100\%$

$\Delta Q=I\Delta t$
$I=Anev$
$W=VQ$
$V=IR$
$R={\frac {\rho L}{A}}$
$P=VI=I^{2}R={\frac {V^{2}}{R}}$
$W=VIt$
$e.m.f=V+Ir$
$V_{\text{out}}={\frac {R_{2}}{R_{1}+R_{2}}}\times V_{\text{in}}$
$R=R_{1}+R_{2}+\cdots$
${\frac {1}{R}}={\frac {1}{R_{1}}}+{\frac {1}{R_{2}}}+\cdots$
- If there are only two resistors, this simplified equation can be used which isn't given in booklet:
  $R={\frac {R_{1}R_{2}}{R_{1}+R_{2}}}$

$f={\frac {1}{T}}$ This is NOT given in the unit 2 section of the booklet but IS given in the unit 4 section.
$v=f\lambda$
$\lambda ={\frac {ax}{D}}$
$E=hf={\frac {hc}{\lambda }}$
$hf=\phi +KE_{\text{max}}$
$\lambda ={\frac {h}{mv}}$
The following equations are NOT given in the formulae booklet
- ${\text{intensity}}={\frac {\text{power}}{\text{cross-section area}}}$
- ${\text{intensity}}\propto {\text{amplitude}}^{2}$
- The following equation is known as Malus's Law:
  - $I=I_{0}cos^{2}{\theta }$
- Malus's Law can also be given in terms of amplitude:
  - $A=A_{0}cos^{2}{\theta }$

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