# 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

### Unit 1 - Mechanics

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

#### Kinematics Equations

• $v = u + a t$
• $a = \frac {\Delta v}{\Delta t} = \frac{v -u}{t}$
• $s = \frac{1}{2}(u + v)t$
• $s = ut + \frac{1}{2}at^2$
• $v^2 = u^2 + 2 a s$

#### Forces, Moments and Pressure

• $F_x = Fcos\theta$
• $F_y = Fsin\theta$
• $F = ma$
• $W = mg$
• $\text{moment} = Fx$
• $\text{torque} = Fd$
• $\rho = \frac{m}{V}$
• $p = \frac{F}{A}$

#### Work, Energy and Power

• $W=F_xcos\theta$
• $E_k = \frac{1}{2}mv^2$
• $E_p = mgh\$
• $P = \frac {\Delta W}{\Delta t}$ Not given in formulae booklet.

#### Deforming Solids

• $F = kx$
• $E = \frac{1}{2}Fx = \frac{1}{2}kx^2$
• $\text{stress} = \frac{F}{A}$
• $\text{strain} = \frac{x}{L}$
• $\text{Young modulus} = \frac{\text{stress}}{\text{strain}}$

### Unit 2 - Electrons, Waves and Photons

#### Electricity

• $\Delta Q = I\Delta t$
• $I = Anev$
• $W=VQ$
• $V=IR$
• $R = \frac{\rho L}{A}$
• $P = VI = I^2 R = \frac{V^2}{R}$
• $W=VIt$
• $e.m.f = V +Ir$
• $V_\text{out} = \frac{R_2}{R_1 + R_2} \times V_\text{in}$
• $R=R_1+R_2+\cdots$
• $\frac{1}{R} = \frac{1}{R_1}+\frac{1}{R_2}+\cdots$
• If there are only two resistors, this simplified equation can be used which isn't given in booklet:
$R = \frac{R_1 R_2}{R_1+R_2}$

#### Waves and Photons

• $f = \frac{1}{T}$ 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:
• $A = A_0 cos^2{\theta}$