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Formulae list

Some of these formulae should be memorised during your higher level course but the list covers a great deal more than is needed for a simple extension to the foundation course. It is most important that you are sure of the meaning of all the symbols

Equations of motion

s = vt
v = u + at
v2 = u2 + 2as
s = ut + at2
average vel. = [u + v]/2


Momentum M = mv
Impulse I = Ft
Newton's second law F = d(mv)/dt = ma
Impulse and momentum Ft = mv mu
Kinetic energy k.e = mv2
Potential energy p.e = mgh
Work work = Fs
Power Power = Fv


Weight (F) = mg
Pressure (P) = F/A
Pressure at a depth h in a liquid in a liquid (P) = hρg
Density (ρ) = m/V
Couple (C) = Fd
Upthrust (U) = vρg


Range (R) = u2sin2A/g
Maximum height (h) = u2sin2A/2g
Time of flight t = 2usinA/g

Motion in a circle

Angular velocity ω = θ/t
Linear and angular velocity v = rω
Time of rotation period T = 2πr/v = 2π/ω
Centripetal force F = mv2/r = mω2r

Rotational dynamics

Moment of inertia (I) = Σmr2
Angular momentum (M) = Iω
Rotational kinetic energy = Iω2
Couple (C) = Iα
Work done W = Cθ

Simple harmonic motion

Acceleration a = -ω2 x
Displacement x = rsin(ωt)
Velocity v = ω√(r2 - x2)
Acceleration a = -ω2rsin(ωt)
Velocity v = ωr cos (ωt)
Kinetic energy = mω2(r2 - x2)
Potential energy = mω2x2
Total energy E = mω2r2


Kepler's third law T2/r3 = constant
Newton's law F = Gm1m2/d2
Potential energy p.e = - GmM/r
Kinetic energy k.e = +GmM/2r
Total energy E = - GmM/2r
Potential VG = - GM/r
go and G go = GM/R2
g and go (r> R) g = goR2/r2
g and go (r < R) g = gor/R
Escape velocity v = √[2Rgo]


Stress   stress = F/A
Strain strain = e/L
Young modulus   E = F/LeA
Bulk modulus   K = Dp/(Dv/v)
Rigidity or shear modulus (G) G = [F/A]/θ
Potential energy stored = Fe = EAe2/L
Energy per unit volume = stress x strain

Thermal expansion

F = EAαθ


Coefficient of friction (μ) F = μR


Coefficient of viscosity (η) F = hA x velocity gradient
Stokes' law F = 6πhrv
Poiseuille's formula Volume s-1 = πhρgr4/8ηl

Surface tension

Capillary rise (h) T cosθ = hrρg/2
Excess pressure in air bubble p = 2T/r
Excess pressure in soap bubble p = 4T/r

Geometrical Optics

Refractive index (n) = sin i/sin r = real depth/apparent depth
Related to wave velocities (n) = cm/cv
Serial relation n1sinθ1 = n2sinθ2
Thin prism   d = (n 1)A
Critical angle(c) n = 1/sin c
Lens formulae 1/u + 1/v = 1/f
Telescope magnification (m) = fo/fe
Angular magnification   M = - (D/f+ 1)
Resolving power f = 1.22λ/a

Physical Optics

Constructive interference path difference for a maximum = mλ
Destructive interference path difference for a minimum= (2m + 1)λ/2
Young's slits   ml = xmd/D
Newton's rings (dark ring viewed by reflection) mλ = rm2/R
Thin film interference mλ = 2nt cos r
Diffraction grating (max)    mλ = e sinθ
Brewster's law (polarisation) tan p = n
Malus' law I = Iocos2θ

Wave motion

Doppler effect Δλ = λv/c Δf = fv/c
Travelling wave y = a sin[ωt kx] = a sin2π[t/T x/λ]
Standing wave y = 2a cos[2πx/λ]sin[2πt/T]
Velocity of sound (v) = √[γP/ρ]
Frequency of stretched string fo = (1/2L)√[T/m]1/2
Fundamental frequency (closed tube) fo = v/4L
Intensity of wave I = ka2
Beat frequency f = f1 f2
Organ pipes:
Open pipe f = (m + 1)fo
Closed at one end f = (2m + 1)fo

Thermal Physics

Scale of temperature t/100 = (Ft F0)/(F100 F0)
Linear expansivity (α) Lθ = L0[1 + αθ]
Specific heat capacity (c) H = mcθ
Specific latent heat (L) H = mL
Electrical heating H = VIt
Density change rθ = ρ0[1+αθ]
Ideal gas equation PV = nRT
Isothermal change PV = constant
Adiabatic change PVγ = constant
Charles's law V/T = constant
Conduction of heat dH/dt = - kA dθ/dx
Stefan-Boltzmann law E = σA[T4 To4]
Wien's law λmax = constant
First law of thermodynamics dU = dQ + dW
Work done in isothermal change dW = PdV
Kinetic theory equation PV = 1/3 mnc2rms
Mean square velocity (crms)2 = v[u12 + u22 + . + un2]/n


Charge Q = It
Current I = nAve
Electrical energy = QV
Force on charge F = QE = QV/d
Ohm's law V = IR
Internal resistance E = I[R + r]
Resistivity ρ= RL/A
Temperature variation Rθ = Ro[1 + αθ]
Series resistance R = R1 + R2
Parallel resistance 1/R = 1/R1 + 1/R2
Power W = VI = I2R = V2/R


Electric field strength E = - dV/dx
Force between point charges F = Q1Q2/[4πεd2]
Field due to point charge Q E = Q/[4εd2]
Potential V = W/Qo
Potential due to charge Q VE = Q/[4πεd]
Capacitance (C) = Q/V
Capacitance of a sphere (C) = 4πεr
Parallel-plate capacitor C = εA/d
Parallel capacitors      C = C1 + C2
Series capacitors      1/C = 1/C1 + 1/C2
Energy (E) stored by a capacitor = CV2 = QV = Q2/C
Capacitor discharge      V = Voe-t/RC
Capacitor charge      V = Vo[1 - e-t/RC]


Couple on coil (C) = BANIsinθ
Field at centre of coil of N turns (B) = μoNI/2r
Field in solenoid (B) = μoNI/L
Field at end of long solenoid of N turns (B) = μoNI/2L
Helmholtz coils field (B) = 8μoNI/5[5]1/2r
Field near straight wire (B) = μoI/2πr
Velocity of e.m. waves c = 1/(εoμo)1/2

Electromagnetic induction

Self-inductance L = Nφ/I
Mutual inductance M = Nsφs/Ip
Induced e.m.f. (ε) = -L dI/dt
Induced e.m.f. (εs) = - MdI/dt
Induced e.m.f. in a rotating coil (ε) = BANωsinθ
Induced e.m.f.(Neumann's law) ε = - Ndφ/dt
Transformer      np/ns = Vp/Vs and Ip/Is = ns/np
Root mean square current (I) I = io/21/2
Alternating current i = io sin(ωt)
Capacitative reactance Xc = 1/ωC
Inductive reactance XL = ωL
Impedance (series RLC) Z = [R2 + (XL _ XC)2]1/2
Resonance condition for I     XL = XC

Electron Physics

Electrostatic f orce on electron F = eE
Electromagnetic force on electron F = Bev
Crossed fields     eE = Bev
Energy gain     E = eV
Kinetic energy      eV = mv2
Circular orbit      Bev = mv2/r
Quantum energy      E = hf
Relativistic mass-energy relation      E = mc2
de Broglie equation λ = h/p = h/mv
Work function     W = hfo
Einstein's p.e. equation     hf = hfo + mv2
Photoelectric effect     hf = eV

Nuclear Physics

Radioactive decay N = Noe-lt
A = Ao/2n Half-life T = ln2/λ
Serial relation λ1N1 = λ2N2
Nuclear radius (r) of nucleus of mass number A = roA1/3


m = mo/[1-v2/c2]
L = Lo[1-v2/c2]
t = to/[1-v2/c2]
γ = 1/[1-v2/c2]1/2 = [1-v2/c2]-1/2
m = γmo
L = Lo
t = γto

© Keith Gibbs