Waves and Electromagnetic Radiation

⇱ All Physics Reference Tables (2025 Edition)
← Energy	The Electromagnetic Spectrum (Physics) →

The Waves and Electromagnetic Radiation page of the Reference Tables for Physical Science: Physics (2025 Edition) is the waves and optics equation sheet: nine equations with the meaning of their variables. Wave speed, period, index of refraction and Snell's law support HS-PS4-1; E_photon = hf supports HS-PS4-3 and HS-PS4-4 (and the physics side of HS-ESS1-2); the law of reflection, the lens equation and magnification support HS-PS4-6. Every equation has its own row anchor.

Equations
v = fλ
T = 1f
Ephoton = hf
θi = θr
n = cv
n1 sin θ1 = n2 sin θ2
n2n1 = v1v2 = λ1λ2
1F = 1do + 1di
hiho = −dido

Variables
c = speed of light in a vacuum
di = distance to image
do = distance to object
Ephoton = energy of photon
F = focal length
f = frequency
h = Planck's constant
hi = image height
ho = object height
n = absolute index of refraction
T = period
v = velocity or speed
λ = wavelength
θ = angle
θi = angle of incidence
θr = angle of reflection

What the waves page shows

Waves. v = fλ relates the speed, frequency and wavelength of any wave; for light and other electromagnetic waves in a vacuum v is c from the List of Physical Constants, and for sound in air the constants list gives 331 m/s. T = 1/f converts between period and frequency.

Photons. E_photon = hf gives the energy of a photon from its frequency, with Planck's constant from the constants list; the electronvolt entry converts the answer to eV. There is no E = hc/λ on the tables, so a wavelength has to go through v = fλ first. This is the only modern-physics equation on the 2025 tables: the 2006 edition's E = mc², the energy-level diagrams and the standard-model tables are gone.

Reflection and refraction. θ_i = θ_r is the law of reflection. n = c/v defines the absolute index of refraction, n₁ sin θ₁ = n₂ sin θ₂ is Snell's law, and the ratio equation says that when light enters a medium of higher index its speed and wavelength drop in the same proportion while its frequency stays the same. The 2006 edition's table of indices of refraction is not in the 2025 edition, so a question gives the indices it needs.

Lenses and mirrors. 1/F = 1/d_o + 1/d_i relates the focal length to the object and image distances, and h_i/h_o = −d_i/d_o gives the magnification; the minus sign means a real image (positive d_i) is inverted. These two equations are new in the 2025 edition, for HS-PS4-6.

Rows

Each row of the table has an anchor, so a link or an {{Rt}} chip (Template:Rt) can point at one equation or constant:

• wave-speed – v = fλ
• period – T = 1/f
• photon-energy – E_photon = hf
• reflection – θ_i = θ_r
• index-of-refraction – n = c/v
• snell – n₁ sin θ₁ = n₂ sin θ₂
• index-ratio – n₂/n₁ = v₁/v₂ = λ₁/λ₂
• lens-equation – 1/F = 1/d_o + 1/d_i
• magnification – h_i/h_o = −d_i/d_o

Regents Exam Questions

Released Regents questions that cannot be answered without this table, listed by exam. Each link opens the question with its answer key; the standard is the one the question assesses.

Exam	Cluster	Question	Standard	Row
June 2026 Physics Regents	Kidney Stone Detection and Removal	Question 7	HS-PS4-1	v = fλ
	Kidney Stone Detection and Removal	Question 10	HS-PS4-1	Ephoton = hf
	Emission Spectra and Nuclear Fusion	Question 22	HS-PS4-1	Ephoton = hf; v = fλ
	The Cell Phone	Question 26	HS-PS4-1	n = c/v
	Flashlight Physics	Question 31	HS-PS4-1	v = fλ
	Voice Recognition Software	Question 44	HS-PS4-1	T = 1/f
Physics sample clusters (spring 2025)	Automotive Optics	Question 2	HS-PS4-6	θi = θr
	Automotive Optics	Question 4	HS-PS4-6	hi/ho = −di/do