Physics Formulas

“Distance between crests“

Wavelength

Formulas relating speed, period and wavelength

v = λ / T and λ = vT

Standing wave, fixed string

L = n (2 / λ) ​ ​

L = string length

n = number of half-waves/loops

Wave on string + tension

FT​ = tension,

μ =mass per unit length

Sound intensity spreads with distance

I = intensity, r =distance

β = dB level

I0 =

Sound interference

First minimum: Δr = λ/2

Δr = path difference ​ ​

Start midway between 2 speakers, walk xxx

Δr = 2x

therefore first minimum gives x = λ / 4

The period of a mass on a spring

m = mass, k = spring constant

Hanging spring equilibrium

mg = kx

x = spring stretch

Spring mechanical energy

A = amplitude

SHM acceleration

acceleration is greatest in magnitude at maximum displacement

Isothermal gas work (use for constant temperature expansion/compression)

Malus's law; θ = angle between polarization directions

Double-slit fringe spacing

d = slit separation; bigger d → fringes closer

Light wavelength from frequency

λ = c/f

c = 3.00×10^8m/s

Critical angle / total internal reflection

light travels from higher n1​ to lower n2

Thin soap film, thinnest bright reflection

t = λ / 4n

t = film thickness, n = refractive index

Coulomb's law

Electric field from point charge/sphere

Electric flux

Φ = EAcosθ​

Φ = flux, A= surface area

Circular area

useful for flux through cylinder ends

Magnetic force on moving charge

EM wave: electric ↔ magnetic field

E = cB ​ so B = E/c

• E = electric field strength, measured in V/m (or N/C)

• B = magnetic field strength, measured in tesla (T)

• c = speed of light

OHM'S LAW

V = IR

V = voltage (V)

I = current (A)

R = resistance (Ω)

Use when: Finding voltage, current, or resistance.

Electrical power / bulb brightness

greater power → brighter bulb

LC circuit frequency

L = inductance

C = capacitance