Chapter 9 · Electrons in Atoms and the Periodic Table
9.2Light: Electromagnetic Radiation
10 min · two checks
Predict
Which relationship connects wavelength and frequency of light?
The idea
- Relate wavelength, frequency, and the speed of light.
- Describe light as a wave with a particle-like energy packet.
Electromagnetic radiation is a coupled electric and magnetic wave traveling, in vacuum, at c = 3.00 × 10⁸ m/s. Wavelength λ is the distance between crests, in meters or nanometers. Frequency ν is how many crests pass a point per second, in hertz (s⁻¹). They are inversely related: c = λν. Red light has a longer wavelength and a lower frequency than violet light.
Light also comes in packets called photons. The energy of one photon is E = hν, where h is Planck’s constant, 6.626 × 10⁻³⁴ J·s. Higher frequency means higher energy per photon. Brightness is about how many photons, not about how energetic each one is. A dim ultraviolet source can still deliver more energy per photon than a bright red lamp.
Keep these
- c = λν, with c = 3.00 × 10⁸ m/s.
- E = hν. High frequency, high energy per photon.
- Wavelength and frequency move in opposite directions.