EM spectrum, refraction practical, completing a line

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🌈 1. Electromagnetic (EM) Spectrum

🔹 What is the EM Spectrum?

  • A range of all types of electromagnetic waves

  • All transfer energy as radiation

  • Travel at speed of light (≈ 3 × 10⁸ m/s) in vacuum

🔹 Order of Waves (Longest → Shortest Wavelength)

Radio → Microwaves → Infrared → Visible light → Ultraviolet → X-rays → Gamma rays

  • Remember: “Rabbits Mate In Very Unusual eXpensive Gardens” 🐰

🔹 Key Properties

Wave

Use

Danger

Radio

Communication

None

Microwaves

Cooking, satellite signals

Burns (high intensity)

Infrared

Heaters, remote controls

Burns

Visible

Sight

None

Ultraviolet

Tanning, sterilisation

Skin damage, eye damage

X-rays

Medical imaging

Cancer risk (high doses)

Gamma rays

Sterilisation, cancer treatment

Extremely dangerous

🔹 Key Idea

  • Wavelength ↓ → Frequency ↑ → Energy ↑

🔹 2. Refraction Practical

🔹 What is Refraction?

  • Bending of light when it passes from one material to another

🔹 Required Practical: Measuring Refraction

Equipment:

  • Rectangular glass block

  • Ray box or laser

  • Protractor

  • Paper

Method:

  1. Draw incident ray hitting block at an angle

  2. Trace refracted ray inside block

  3. Trace emergent ray leaving block

  4. Measure angles of incidence, refraction, emergence

  5. Compare with Snell’s law (optional higher level)

Observations:

  • Light bends towards normal in denser medium

  • Light bends away from normal in less dense medium

🔹 3. Completing a Line (Physics Concept)

  • Often seen in practical graphs or ray diagrams

  • Example:

    • Extend a refracted ray

    • Draw a normal

    • Complete line of emergent light

Key Tips:

  • Always label:

    • Incident ray

    • Refracted ray

    • Emergent ray

    • Normal

🔗 Big Links

  • EM spectrum → different types of waves & energy

  • Refraction → behaviour of visible light

  • Completing a line → practical & diagram skills

⭐ Exam Tips

  • EM spectrum: longest → shortest wavelength, properties, uses, dangers

  • Refraction: incident, refracted, emergent rays, normal, angle measurement

  • Diagrams: use ruler, pencil, label clearly