Stopping potential equals maximum kinetic energy (in eV) divided by e, so to stop 4.2 eV electrons the anode must be at -4.2 V relative to cathode.

Ultraviolet radiation can cause burns (sunburn) on human skin.

Einstein's photoelectric relation equates photon energy hf to the maximum kinetic energy 1/2 mv^2 of emitted electrons.

Fraunhofer lines are the dark absorption lines observed in the solar spectrum produced by elements in the Sun's atmosphere.

Apparent frequency shifts in starlight are due to the Doppler effect from relative motion between source and observer.

If λm·T is constant, increasing T requires λm to decrease, so the maximum shifts to shorter wavelengths as temperature rises.

Wavelengths around 1 Å (10^-10 m) lie in the X-ray region of the electromagnetic spectrum.

A single quantum of electromagnetic radiation is called a photon.

An oscillator produces a continuous sinusoidal signal of constant amplitude, suitable for generating radio waves.

Light waves are electromagnetic transverse waves with oscillations perpendicular to the direction of propagation.