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1.3.1Additional lessons

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

5 min read 5 parts Lesson 8 of 172

📚 IB Chemistry HL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 5Regions of the Spectrum

Electromagnetic radiation covers a continuous range of wavelengths and energies, all travelling at the speed of light in a vacuum.

Order
  • Order From low to high energy: radio, microwave, infrared, visible, ultraviolet, X-ray and gamma ray.
Visible light
  • Visible light Wavelengths from about 400 nm (violet) to about 700 nm (red), with the other colours between.
Long wavelength
  • Long wavelength Radio waves and microwaves have long wavelengths, low frequency and low energy.
Short wavelength
  • Short wavelength Ultraviolet, X-rays and gamma rays have short wavelengths, high frequency and high energy.

Part 2 of 5Key Relationships

Key Relationships
Wave equation
  • Wave equation c = λν, where c = 3.00 × 10⁸ m s⁻¹ is the speed of light, λ is wavelength and ν is frequency.
Photon energy
  • Photon energy E = hν, where h = 6.63 × 10⁻³⁴ J s is the Planck constant.
Inverse
  • Inverse Frequency and wavelength are inversely proportional, as the speed is constant.
Direct
  • Direct Photon energy is directly proportional to frequency, so shorter wavelength means higher energy.
RegionTypical use or effect
InfraredMakes bonds vibrate; felt as heat
VisibleCan promote electrons in some compounds, giving colour
UltravioletCan break bonds and cause sunburn
X-raysCan remove inner electrons; used in imaging

Part 3 of 5Interaction with Matter

The energy of the radiation decides what happens when it is absorbed.

1
Low-energy microwaves cause molecules to rotate more quickly.
2
Infrared radiation causes bonds to vibrate with greater amplitude.
3
Visible and ultraviolet radiation can promote electrons to higher energy levels.
4
High-energy ultraviolet radiation can break covalent bonds, which is how it can damage skin cells.
5
Very high-energy X-rays and gamma rays can remove electrons completely and ionise atoms.

Part 4 of 5Worked Example

Question Calculate the frequency and photon energy of light with wavelength 500 nm.

  1. ν = c ÷ λ = 3.00 × 10⁸ ÷ 5.00 × 10⁻⁷ = 6.00 × 10¹⁴ Hz.
  2. 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 per photon

Part 5 of 5Exam Checklist & Tips

1.3.1 – Key Points for the Exam

  • Wavelength The distance between two successive crests of a wave.
  • Frequency The number of wave cycles passing a point each second, measured in hertz.
  • Photon A packet of electromagnetic energy of size hν.
  • Planck constant h = 6.63 × 10⁻³⁴ J s.

Common Mistakes

  • Using wavelength in nm without converting to metres in c = λν.
  • Stating that violet light has lower energy than red light.
  • Thinking that radiation with long wavelength has high frequency.
  • Forgetting that E = hν gives the energy of one photon, not one mole.

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Transformer Golden Equations Physics Standard

Transformer Turns Ratio & Efficiency

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

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