Waves, Light and Electromagnetism
MYP Unit Framework
Key Concept: RELATIONSHIPS Related Concepts: Energy. Models. Patterns. Global Context: Scientific and Technical Innovation (How do the fundamental relationships between energy, matter, and information underpin modern technology?) Statement of Inquiry: The behaviour of waves reveals fundamental relationships between energy, matter, and information that underpin modern technology.
Inquiry Questions
| Type | Question |
|---|---|
| Factual | What are the properties of waves? What is the electromagnetic spectrum? What is the difference between transverse and longitudinal waves? What is Ohm's law? |
| Conceptual | How can a wave carry ENERGY without carrying MATTER? What is the relationship between electricity and magnetism? How do we KNOW that light is a wave? |
| Debatable | Should we be concerned about the health effects of electromagnetic radiation (mobile phones, Wi-Fi)? Is the benefits of medical imaging worth the radiation RISK? |
1. Wave Properties — The Basics
What Is a Wave?
'A wave is a DISTURBANCE that transfers ENERGY from one place to another WITHOUT transferring matter. The medium (water, air, a slinky) oscillates — but does not TRAVEL with the wave. A cork on the ocean bobs UP and DOWN as a wave passes — it does not move HORIZONTALLY with the wave.'
Types of Waves
| Type | Description | Example |
|---|---|---|
| Transverse | Oscillation is PERPENDICULAR to the direction of energy transfer | Light, water waves, waves on a string |
| Longitudinal | Oscillation is PARALLEL to the direction of energy transfer | Sound waves, seismic P-waves |
Key Quantities
- Amplitude (A): Maximum displacement from equilibrium. 'Larger amplitude = MORE ENERGY. A loud sound has a LARGER amplitude than a soft one.'
- Wavelength (λ): Distance between two consecutive crests or troughs.
- Frequency (f): Number of complete oscillations per second. Unit: HERTZ (Hz). 1 Hz = 1 oscillation per second.
- Period (T): Time for one complete oscillation. T = 1/f.
- Wave speed (v): v = f × λ. 'The wave equation is ONE of the most useful relationships in physics — it applies to ALL waves, from sound to light to seismic waves.'
The Wave Equation v = f × λ
'This equation tells you that frequency and wavelength are INVERSELY PROPORTIONAL — if frequency increases, wavelength must decrease (assuming constant speed). This is why BLUE light (high frequency) has a SHORTER wavelength than RED light (low frequency).'
2. The Electromagnetic Spectrum
What Is Electromagnetic Radiation?
'Electromagnetic (EM) radiation consists of OSCILLATING electric and magnetic fields that travel through space at the SPEED OF LIGHT (3.0 × 10⁸ m/s in a vacuum). EM waves are TRANSVERSE and do NOT require a medium — they can travel through the vacuum of space. This is why we can see the Sun.'
The Spectrum
'The EM spectrum is a CONTINUUM of all types of electromagnetic radiation, ordered by FREQUENCY and WAVELENGTH. As frequency INCREASES, wavelength DECREASES — and energy INCREASES.'
| Region | Wavelength | Frequency | Uses / Sources |
|---|---|---|---|
| Radio waves | > 0.1 m | < 3 × 10⁹ Hz | Radio, TV, Wi-Fi, mobile phones, radar |
| Microwaves | 1 mm – 0.1 m | 3 × 10⁹ – 3 × 10¹¹ Hz | Microwave ovens, satellite communication, radar |
| Infrared (IR) | 700 nm – 1 mm | 3 × 10¹¹ – 4.3 × 10¹⁴ Hz | Heat radiation, remote controls, thermal imaging |
| Visible light | 400 – 700 nm | 4.3 × 10¹⁴ – 7.5 × 10¹⁴ Hz | Human vision, photography, fibre optics |
| Ultraviolet (UV) | 10 – 400 nm | 7.5 × 10¹⁴ – 3 × 10¹⁶ Hz | Sun tanning, sterilisation, vitamin D synthesis |
| X-rays | 0.01 – 10 nm | 3 × 10¹⁶ – 3 × 10¹⁹ Hz | Medical imaging, airport security, crystallography |
| Gamma rays | < 0.01 nm | > 3 × 10¹⁹ Hz | Cancer radiotherapy, nuclear medicine, astronomy |
Energy and Danger
'As frequency increases, the energy carried by each photon INCREASES. Radio waves are LOW energy — they pass through our bodies WITHOUT causing harm. Gamma rays are HIGH energy — they can IONISE atoms, damage DNA, and cause CANCER. This is why X-ray technicians stand BEHIND a lead shield.'
3. Light — Reflection, Refraction, and Lenses
Reflection
'Light reflects off surfaces according to the LAW OF REFLECTION: angle of incidence = angle of reflection. Both angles are measured from the NORMAL (a line perpendicular to the surface).'
Types of reflection:
- Specular reflection: Light reflects off a SMOOTH surface — producing a clear IMAGE (mirror).
- Diffuse reflection: Light reflects off a ROUGH surface — scattering in many directions. This is how we see MOST objects — they reflect light diffusely toward our eyes.
Refraction
'Light CHANGES DIRECTION (bends) when it passes from one medium to another — because its SPEED changes. This is REFRACTION.'
Snell's law: n₁ sin θ₁ = n₂ sin θ₂ where n is the REFRACTIVE INDEX of the medium. 'The refractive index measures how much a medium SLOWS down light. Diamond has a high refractive index (2.42) — which is why it SPARKLES.'
Applications: Lenses (converging and diverging). Fibre optics (total internal reflection — light is TRAPPED inside a glass fibre and can travel for KILOMETRES with minimal loss). Prisms. Rainbows.
Lenses and Image Formation
'CONVERGING lenses (convex) bring parallel light rays to a FOCUS. DIVERGING lenses (concave) spread them out. The FOCAL LENGTH (f) is the distance from the lens to the focal point. The POWER of a lens is 1/f (unit: dioptres).'
Real vs. virtual images: 'A REAL image can be PROJECTED onto a screen — light rays actually CONVERGE at that point. A VIRTUAL image CANNOT be projected — the light rays only APPEAR to diverge from that point. Your eye's lens produces a REAL image on your retina. A magnifying glass produces a VIRTUAL image.'
4. Electrical Circuits
Current, Voltage, and Resistance
- Current (I): The flow of ELECTRIC CHARGE. Unit: AMPERE (A). 1 A = 1 coulomb per second. Current is measured with an AMMETER connected in SERIES.
- Voltage (V): The ENERGY PER UNIT CHARGE provided by a power source or used by a component. Unit: VOLT (V). Voltage is measured with a VOLTMETER connected in PARALLEL.
- Resistance (R): A measure of how much a component OPPOSES the flow of current. Unit: OHM (Ω).
Ohm's Law
V = I × R: 'The voltage across a resistor equals the current through it multiplied by its resistance. Ohm's law is FUNDAMENTAL to circuit analysis. But not all components obey it — diodes, transistors, and light bulbs show NON-OHMIC behaviour.'
Series and Parallel Circuits
| Feature | Series | Parallel |
|---|---|---|
| Current | Same through ALL components | Divides between branches |
| Voltage | Divides between components | Same across ALL branches |
| Total resistance | R_total = R₁ + R₂ + ... | 1/R_total = 1/R₁ + 1/R₂ + ... |
| If one component fails | ALL stop working | Others continue working |
5. Electromagnetism
The Connection Between Electricity and Magnetism
'Electricity and magnetism are TWO FACES of the same fundamental force — ELECTROMAGNETISM. A moving electric charge CREATES a magnetic field. And a changing magnetic field CREATES an electric current.'
Electromagnets
'A current-carrying wire produces a MAGNETIC FIELD around it. Coiling the wire (solenoid) CONCENTRATES the field. Adding an IRON CORE STRENGTHENS it further. This is an ELECTROMAGNET — and it can be turned ON and OFF, unlike a permanent magnet.'
Applications: Electric motors, generators, doorbells, MRI machines, particle accelerators.
Electromagnetic Induction
'When a CONDUCTOR moves through a magnetic field — or when a magnetic field CHANGES around a stationary conductor — a VOLTAGE is INDUCED. This is ELECTROMAGNETIC INDUCTION, discovered by Michael Faraday in 1831.'
'Faraday's law: The magnitude of the induced voltage is proportional to the RATE OF CHANGE of the magnetic flux. This is GENERATOR PRINCIPLE — mechanical energy is converted into electrical energy.'
Applications: Generators (ALL electricity in the grid is produced this way — coal, gas, nuclear, hydro, wind). Transformers (step up voltage for long-distance transmission, step down for safe home use). Induction cooktops. Wireless charging.
6. Applications — Medical Imaging and Telecommunications
Medical Imaging
| Technology | Type of EM radiation | Principle | Use |
|---|---|---|---|
| X-ray | X-rays | Different tissues absorb X-rays differently | Bone fractures, chest infections |
| CT scan | X-rays | Multiple X-ray images from different angles combined by computer | Detailed 3D images of organs |
| MRI | Radio waves (in strong magnetic field) | Protons in water molecules align with magnetic field and emit radio signals | Soft tissue imaging (brain, muscles, joints) |
| Ultrasound | Sound waves (NOT EM) | High-frequency sound waves reflect off internal structures | Pregnancy scans, heart imaging |
Telecommunications
'The entire modern communication system — radio, television, mobile phones, Wi-Fi, satellite communication — depends on ELECTROMAGNETIC WAVES. Information is ENCODED by modulating the wave: AM (amplitude modulation) or FM (frequency modulation) for radio, QAM (quadrature amplitude modulation) for digital signals.'
Fibre optics: 'Light pulses travel through GLASS FIBRES using TOTAL INTERNAL REFLECTION. Fibre optic cables can carry ENORMOUS amounts of data at the SPEED OF LIGHT — millions of times more data than copper cables of the same diameter.'
Your Summative Assessment — The Practical Investigation
Task: Design and conduct an experiment to investigate how ONE variable affects the behaviour of waves (e.g., how the angle of incidence affects the angle of refraction through a glass block, how the resistance of a wire depends on its length, or how the strength of an electromagnet depends on the number of coils). Write a FULL LAB REPORT following the scientific method: Aim, Hypothesis (with scientific reasoning), Variables (independent, dependent, controlled), Method (diagram included), Results (table and graph), Conclusion, and Evaluation (sources of error, reliability, suggestions for improvement).
'This assessment develops the PRACTICAL and ANALYTICAL skills needed for IB DP Sciences Internal Assessments across all science subjects.'
ATL Skills
| Skill | Focus |
|---|---|
| Critical Thinking | Designing experiments, analysing data, evaluating evidence. Evaluating model validity. |
| Research | Investigating real-world applications of waves and electromagnetism. |
| Communication | Writing a structured lab report. Using scientific conventions (units, symbols, diagrams). |
| Self-Management | Working safely with electrical equipment and following experimental procedures. |
Formative Assessments
| Assessment | Focus |
|---|---|
| Wave properties worksheet | Label and calculate amplitude, wavelength, frequency, and wave speed for given wave diagrams. |
| EM spectrum poster | Create a poster showing the EM spectrum with wavelengths, frequencies, and uses for each region. |
| Circuit-building lab | Build series and parallel circuits. Measure current and voltage. Verify Ohm's law. |
| Electromagnet construction | Build an electromagnet and investigate how the number of coils affects its strength. |
Interdisciplinary Connections
- Biology: Medical imaging technology, eye anatomy and vision, effects of radiation on living tissue.
- Mathematics: Trigonometry in wave analysis, inverse square law, logarithms in decibel scales.
- Chemistry: Spectroscopy, EM radiation in chemical analysis, quantum theory of light.
- TOK: Can we TRUST what our senses tell us about the world — given that most of the EM spectrum is INVISIBLE to us?
Service as Action
- Science outreach: Demonstrate wave phenomena (e.g., ripple tank, microwave experiments) to younger students.
- Electronics repair workshop: Learn and teach basic electronics repair to reduce e-waste.
- Technology history project: Research and present the history of a communication technology (radio, television, internet) and its social impact.
IB Learner Profile Attributes
| Attribute | How This Unit Develops It |
|---|---|
| Inquirers | Students ask questions about the fundamental nature of light, waves, and electromagnetism. |
| Knowledgeable | Students build deep understanding of the electromagnetic spectrum and its applications. |
| Thinkers | Students solve problems involving wave calculations and circuit analysis. |
| Reflective | Students reflect on the impact of electromagnetic technologies on society and daily life. |
Self-Test Questions
-
Define amplitude, wavelength, frequency, and wave speed. Give the formula relating them.
-
What is the difference between transverse and longitudinal waves? Give ONE example of each.
-
List the regions of the electromagnetic spectrum in order of INCREASING frequency. Give ONE use for each.
-
State the law of reflection and Snell's law. Explain the difference between reflection and refraction.
-
State Ohm's law. Calculate the current through a 12 Ω resistor connected to a 6 V battery.
-
Compare series and parallel circuits across THREE features.
-
What is electromagnetic induction? Give TWO applications.
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Choose ONE medical imaging technology. Explain the physics behind it and name ONE advantage and ONE limitation.
