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1.3.1Additional lessons

The Electromagnetic Spectrum — IB Chemistry SL Revision Notes & Topical Questions

5 min read 5 parts Lesson 7 of 98

📚 IB Chemistry SL Hub / Topical Revision
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Part 1 of 5The Regions

1.3.1 The Electromagnetic Spectrum

Electromagnetic radiation forms a continuous range, divided by wavelength and frequency.

Radio waves
  • Longest wavelengths and lowest frequencies and energies, used in broadcasting and in NMR spectroscopy.
Microwaves and infrared
  • Intermediate-energy regions; infrared makes bonds vibrate and is used in IR spectroscopy.
Visible light
  • A narrow band between about 400 nm (violet) and 700 nm (red) that the human eye can detect.
Ultraviolet and X-rays
  • Higher-energy radiation, where ultraviolet can break bonds and X-rays are used to study crystal structure.
Gamma rays
  • The shortest wavelengths and highest frequencies and energies, produced in nuclear processes.

Part 2 of 5Relationships

All electromagnetic waves travel at the speed of light in a vacuum.

1
The speed of light is c = 3.00 × 10⁸ m s⁻¹, and it is the same for all electromagnetic radiation in a vacuum.
2
Wavelength and frequency are related by c = λν, so a shorter wavelength means a higher frequency.
3
Photon energy is given by E = hν, where h is the Planck constant, 6.63 × 10⁻³⁴ J s.
4
Combining the two relations shows energy is inversely proportional to wavelength, so short waves carry more energy per photon.
RegionWavelengthFrequencyEnergy
RadioLongestLowestLowest
VisibleMiddleMiddleMiddle
GammaShortestHighestHighest

Part 3 of 5Within the Visible Region

Within the Visible Region
Red light
  • Has the longest wavelength and the lowest frequency of the visible colours, and so the lowest photon energy.
Violet light
  • Has the shortest wavelength and the highest frequency of the visible colours, and so the highest energy.
White light
  • A mixture of all visible wavelengths, which a prism can separate into a continuous spectrum.
Continuous spectrum
  • Contains all wavelengths in a range with no gaps, unlike the line spectrum of an atom.

Part 4 of 5Worked Example

Question

  • Green light has a wavelength of 500 nm.
  • Calculate its frequency and the energy of one photon.

  1. λ = 500 nm = 5.00 × 10⁻⁷ m.
  2. ν = c ÷ λ = 3.00 × 10⁸ ÷ 5.00 × 10⁻⁷ = 6.00 × 10¹⁴ Hz.
  3. E = hν = 6.63 × 10⁻³⁴ × 6.00 × 10¹⁴ = 3.98 × 10⁻¹⁹ J.

Answer ν = 6.00 × 10¹⁴ Hz; E = 3.98 × 10⁻¹⁹ J

Part 5 of 5Exam Checklist & Tips

1.3.1 – Key Points for the Exam

  • Wavelength The distance between two successive crests of a wave, symbol λ, in metres.
  • Frequency The number of waves passing a point per second, symbol ν, in hertz.
  • Photon A packet of electromagnetic energy with energy E = hν.
  • Planck constant The constant h = 6.63 × 10⁻³⁴ J s linking photon energy to frequency.

Common Mistakes

  • Saying that red light has more energy than blue because it is hotter.
  • Forgetting to convert nanometres to metres before using c = λν.
  • Claiming that wavelength and frequency are directly proportional; they are inversely proportional.
  • Thinking that different electromagnetic waves travel at different speeds in a vacuum.

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Ratio: Vp / Vs = Np / Ns = Is / Ip

  • Step-up reduces grid thermal loss (P = I2R).
  • Laminated core prevents eddy currents.