A2 Physics Formulas

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Exponential decay

In capacitors

Q_t = Q₀e^-t/RC

Charge at time t is equal to charge at time t = 0 times e to the power –t / RC, where R means resistance in Ohms and C means capacitance in Farads

V_t = V₀e^-t/RC

I_t = I₀e^-t/RC

Q = charge

V = potential difference

I = current

e ≈ 2.718

t = time

R = resistance in Ohms, Ω

C = capacitance in Farads, F

X_t = value of X at time t

X₀ = initial value of X

In optical fibres

I_x = I₀e^-μx

I₀ = original light intensity

I_x = intensity at distance x along fibre

μ = absorption coefficient of optical fibre in per metres, m^-1

x = distance along fibre from original light source

Nuclear Physics

E=mc²

Can be rewritten as…

ΔE = c²Δm

…which means the change in energy is equal to the change in mass times the speed of light squared

Circular Motion

v=ωr

Velocity in a straight line is equal to angular velocity times radius

T = 2π/ω

Time period is equal to circumference (in radians) divided by angular velocity

a = v²/r

Acceleration is equal to linear velocity squared divided by radius

a = rω²

Acceleration is equal to radius times angular velocity squared