Properties of electromagnetic waves 2 production and hazards (HT)

SPEC 4.6.2.3 • PROPERTIES OF EM WAVES — PRODUCTION & HAZARDS

Producing EM Waves & Hazards

How radio waves are made, why high-frequency radiation damages DNA, and the 15%-scoring Jun 2024 question that's coming back.

⚠ PRODUCTION HALF IS HIGHER TIER ONLY · HAZARDS HALF IS BOTH TIERS

Why This Lesson Matters

Both halves of this topic are reliably examined every series. The production half (HT) trips up most students; the hazards half is recall but easy to lose marks on phrasing.

15%

Scored any marks on "how radio waves of a specific frequency are produced" (Jun 2024 HT)

2/2

Mark scheme points — and MP2 is dependent on MP1

~6

Marks per series across the two halves

What You'll Walk Away With

The two-part mark-scheme phrase for radio wave production, the bidirectional concept (radio waves both produce AND are produced by AC), the ionising boundary on the EM spectrum, and the DNA-link phrasing for ionising hazards.

Key Definitions

Three terms underpin this entire topic. The "ionising / non-ionising" split is the single most-important distinction in 4.6.2.3.

Oscillation

A repeated back-and-forth movement about a central position. In an antenna, electrons oscillate up and down — this oscillation is what produces the radio wave.

Ionising Radiation

Radiation with enough energy per photon to knock electrons out of atoms, creating ions. UV, X-rays, and gamma rays are ionising. Radio, microwaves, IR, and visible light are non-ionising — they cannot ionise atoms (though some can still cause harm by heating).

Radiation Dose (Sieverts)

A measure of the risk of harm to body tissue from an exposure to ionising radiation. Measured in sieverts (Sv). 1000 mSv = 1 Sv. You won't be asked to recall the unit name, but you need to know dose = risk.

How Each EM Wave Is Produced

Different EM waves come from different physical sources. The two with strict spec-required answers are radio waves (oscillating circuits) and gamma rays (changes in the nucleus).

What's HT vs Both Tiers

Only radio-wave production via oscillating circuits is HT-only per spec. The general principle that "changes in atoms and nuclei produce EM waves" — covering UV, X-rays, and gamma — is both tiers.

EM TypeProduced ByTier

Radio wavesOscillations in electrical circuits — an alternating current in an antenna causes electrons to oscillate, emitting radio waves of the same frequency as the ACHT only

MicrowavesOscillating circuits (extension of the radio principle — not strictly spec)HT principle

InfraredAll objects above absolute zero (hotter = more IR)Both

Visible lightVery hot objects; electron transitions in atomsBoth

UltravioletChanges in atoms — electrons drop between energy levels, releasing high-energy photonsBoth

X-raysChanges in atoms — high-energy electron transitions between energy levelsBoth

Gamma raysChanges in the nucleus of an atom (radioactive decay) — spec verbatimBoth

Spec Phrase to Memorise

From 4.6.2.3 verbatim: "Changes in atoms and the nuclei of atoms can result in electromagnetic waves being generated or absorbed over a wide frequency range. Gamma rays originate from changes in the nucleus of an atom. "

Radio Wave Production HT

This is the topic that scored 15% in Jun 2024. The mark scheme demands two specific points — and the second is dependent on the first.

MP1

Radio waves are produced by oscillations in an electrical circuit — an alternating current drives oscillating charges (electrons) in the antenna.

MP2

The radio waves have the same frequency as the oscillations (the same frequency as the AC). To transmit at 100 MHz, you drive the antenna with an AC at 100 MHz. MP2 is only awarded if MP1 is stated.

Radio Waves Work Both Ways HT

The process is symmetric. An antenna can transmit radio waves orreceive them — and the spec explicitly examines both directions.

The Reverse Process — Spec 4.6.2.3 Verbatim

"When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical circuit."

TRANSMITTING

AC in circuit → oscillating electrons in antenna → radio waves emitted at the same frequency as the AC

RECEIVING

Radio waves absorbed → induce oscillating charges → AC at the same frequency as the radio wave appears in the circuit

Where This Has Been Tested

Nov 2020 P2 Q06.2 asked the reverse: a circuit absorbs a radio wave — what happens? Mark scheme: (alternating) current induced (in the electrical circuit) with the same frequency as the radio wave. The "same frequency" half is still the most-missed point.

UV, X-rays & Gamma — Where They Come From

Above visible light, the production mechanism switches from circuit oscillations to atomic and nuclear processes. Higher energies per photon — which is why this end of the spectrum is dangerous.

UV & X-rays — Atomic Changes (Both Tiers)

Produced by changes in atoms — electrons drop from a higher energy level to a lower energy level inside an atom, releasing the energy difference as a photon. The bigger the energy gap, the higher the frequency of the photon emitted. UV comes from lower-energy transitions; X-rays from higher-energy transitions.

Gamma Rays — Nuclear Changes (Both Tiers)

Produced by changes in the nucleus of an atom — typically when an unstable nucleus undergoes radioactive decay and emits energy as a gamma photon. This is the spec's exact wording. Saying "gamma comes from electrons" loses the mark.

Why "High Frequency = High Energy" Matters Here

Photon energy is proportional to frequency. Gamma photons carry hundreds of thousands of times the energy of visible light photons — more than enough to knock electrons out of atoms (ionisation), which is why they damage cells.

The Ionising Boundary

The single most-asked fact in EM hazard questions. The boundary sits between visible light and ultraviolet. Below it, EM waves can heat or burn but can't ionise. Above it, photon energies are high enough to strip electrons from atoms.

The Rule

Non-ionising (radio · microwave · IR · visible): cannot strip electrons from atoms. Some can still cause harm (heating, burns) but not by ionising. Ionising (UV · X-rays · gamma): can knock electrons out of atoms, leading to chemical damage and DNA mutation in cells.

Hazards by EM Wave Type

The mark scheme awards different language for different hazards. Match the hazard to the mechanism — generic "it's dangerous" answers score zero.

What the Spec Mandates

Spec 4.6.2.3 only names UV, X-rays, and gamma rays as having hazardous effects on body tissue. The other rows below (microwaves, IR, visible) are real physics and appear in past papers, but are not strict spec content — treat as supporting context.

EM TypeHazardMechanism

RadioNone at typical exposuresNon-ionising; very low photon energy

MicrowavesInternal heating of body tissueWater molecules absorb microwaves and heat up

InfraredSkin burns at high intensitySurface heating of skin

Visible lightEye damage at very high intensity (e.g. lasers, sun)Retinal damage from absorbed energy

Ultraviolet ⚠Premature skin ageing · skin cancerIonising; damages skin cells

X-rays ⚠Mutation of genes · cancerIonising; damages DNA in cells

Gamma rays ⚠Mutation of genes · cancerIonising; damages DNA in cells

⚠ = spec-mandated hazard (4.6.2.3)

Dose Matters

The spec says hazardous effects "depend on the type of radiation AND the size of the dose". A single chest X-ray is far safer than continuous gamma exposure. The risk scales with both — quote both factors in answers about safety.

UV — The Specific Mechanism

UV is the lowest-energy ionising radiation. It doesn't penetrate deeply, but it damages skin cells where it's absorbed — and that's enough.

Spec 4.6.2.3 — Verbatim Language

"Ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer."

The Two Effects

Premature skin ageing: UV damages collagen and elastin in the skin, causing wrinkles and loss of elasticity earlier than normal ageing would.

Skin cancer: UV is energetic enough to damage DNA in skin cells. Damaged DNA can lead to uncontrolled cell division — cancer.

The Word That Examiners Want

The phrase "increase the risk of" — not "causes" — matches spec wording exactly. Sunscreen reduces UV exposure, which reduces risk; it doesn't make cancer impossible.

X-rays & Gamma — The DNA Link

Higher-energy ionising radiation. The mark scheme requires a specific chain: ionising → damages DNA / mutates genes → cancer. Skipping any link costs marks.

Spec 4.6.2.3 — Verbatim Language

"X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer."

1

Ionising radiation — high-energy photons strip electrons from atoms in body tissue.

2

Damage to DNA / mutation of genes — ionisation in or near DNA molecules alters their structure.

3

Cancer — mutated cells can divide uncontrollably, forming tumours.

Common Marking Trap

"Gamma rays cause cancer" — by itself — is a weak Level 1 answer. You must include the mechanism: ionising → DNA / genes → mutation → cancer. Examiner reports flag this every series.

Radiation Dose — A Measure of Risk

The spec covers radiation dose conceptually. You don't need to recall the unit name, but you need to understand what dose means — and that risk scales with both type and dose.

Radiation Dose

A measure of the risk of harm resulting from an exposure of the body to ionising radiation. Measured in sieverts (Sv).

Conversion

1000 mSv = 1 Sv

Two Factors That Decide Harm

Type of radiation: different types of ionising radiation have different ionising power — for the same energy delivered, more ionising types cause more biological damage. (The alpha/beta/gamma comparison sits in topic 4.4 — atomic structure.)

Size of the dose: a single chest X-ray ≈ 0.02 mSv (negligible). Whole-body CT scan ≈ 10 mSv (one-off risk small). Sustained high doses = serious harm.

Drawing Conclusions From Data — Spec-Required Skill

The spec says you should be able to draw conclusions from data about radiation risk. Example:WorkerAnnual dose (mSv)Compared to UK background (~2.5 mSv/yr)A3.5Slightly above background — low extra riskB18.0~7× background — highest additional cancer riskC2.1At background level — no significant extra riskConclusion: Worker B has by far the greatest dose and the highest additional risk of harm. Workers A and C are close to background and face minimal additional risk.

Examiner Tip — Data Questions

Always compare doses to the natural background (~2.5 mSv/year UK). The bigger the dose relative to background, the higher the additional risk. State the comparison numerically where possible.

Examiner Alert — Q06.4 (Jun 2024)

"Many students could not explain how radio waves of a specific frequency are produced. Students that achieved the first mark point usually mentioned alternating current. Only 15% scored any marks here." — AQA Jun 2024 Paper 2H examiner reporting on Q06.4

The Mark Scheme

MP1: radio waves are produced by oscillations in electrical circuits (allow: alternating current; oscillating electrons in an aerial)

MP2: the radio waves have the same frequency as the oscillations

MP2 is dependent on MP1. Say "AC" alone and score 1/2. Say "same frequency" without first saying AC/oscillations and score 0/2.

Why So Many Failed

The most common loss: students wrote about where radio waves are used or what they do instead of how they're produced. The question is mechanism, not application. Read the verb in the question: "explain how... produced" → mechanism.

Strong vs Weak — Same Question

The Jun 2024 question, two student answers. The difference is the explicit frequency-match phrase.

✗ 0/2

"Radio waves are produced by electrons in an aerial. They are sent out from antennas and used for radio broadcasts."

No mention of oscillations / AC . No mention of matching frequency . Just describes what radio waves do.

✓ 2/2

"Radio waves are produced by oscillating electrons in an antenna driven by an alternating current. The radio waves emitted have the same frequency as the alternating current."

Three Keywords That Score

"Alternating current" (or "oscillations in circuit") · "Same frequency" · "As the AC / oscillations". Three phrases. Build them into every radio-production answer.

Three Errors That Cost Marks

Recurring across multiple examiner reports. Memorise the correct phrasing for each.

✗ Wrong

"Radio waves are ionising."Radio is at the lowest-energy end — never ionising.

✓ Right

"Radio, microwaves, infrared and visible light are non-ionising. UV, X-rays and gamma are ionising."Match each EM type to its side of the boundary.

✗ Wrong

"Gamma rays cause cancer."Skips the mechanism — partial credit only.

✓ Right

"Gamma rays are ionising; they cause mutation of genes / damage DNA, which can lead to cancer."Ionising → DNA / genes → mutation → cancer. Full chain.

✗ Wrong

"Radio waves are produced by an electric current in an aerial."Missing "alternating" and "same frequency".

✓ Right

"Radio waves are produced by an alternating current in an aerial; the radio wave has the same frequency as the AC."Both halves of the two-mark answer.

Practice Question

(a) A radio transmitter broadcasts at a frequency of 95.8 MHz. Explain how the radio waves are produced. 2 marks · HT

(b) Explain why X-rays and gamma rays are hazardous to body tissue. 3 marks

Part (a) — 2 marks

MP1

Radio waves are produced by oscillating charges (electrons) in an antenna driven by an alternating current.

MP2

The radio waves have the same frequency as the alternating current — so to produce 95.8 MHz radio waves, the AC must oscillate at 95.8 MHz.

Part (b) — 3 marks

MP1

X-rays and gamma rays are ionising radiation — they have enough energy per photon to knock electrons out of atoms in body tissue.

MP2

This ionisation damages DNA in cells / causes mutation of genes.

MP3

Damaged DNA can lead to uncontrolled cell division, which can cause cancer. (The risk depends on both the type of radiation and the size of the dose.)

Framework — PEE for "Explain" Questions

4.6.2.3 questions are almost all "explain" questions. The PEE framework — Point, Evidence, Explain — maps directly onto the two-mark-point structure the mark scheme uses.

Worked example: Explain how a mobile phone transmits radio waves of a specific frequency to a base station. 3 marks · HT

P — Point (state the mechanism)

The mobile phone produces radio waves by causing oscillations in an electrical circuit connected to an antenna.

E — Evidence (the specific physics)

An alternating current in the circuit causes oscillating charges (electrons) in the antenna. These oscillating charges emit electromagnetic waves.

E — Explain (link to the frequency)

The frequency of the radio wave equals the frequency of the alternating current. So to transmit at a specific frequency (e.g. 900 MHz for a mobile signal), the AC in the circuit must oscillate at that same frequency.

Why PEE Wins on This Topic

Examiner reports show students lose marks by leaping to the conclusion ("same frequency") without laying the mechanism first. PEE forces the mechanism (P + E) before the explanation (final E) — and that ordering matches the dependency structure of the mark scheme.

Three Things to Remember

The three habits that move radio-production and EM-hazard answers from 0/2 to full marks.

1. The Two-Part Radio Production Phrase (HT)

Every radio-production answer needs both halves: (a) oscillations in electrical circuit / alternating current; (b) same frequency as the AC. Without MP1, MP2 cannot score. Lock the phrase: "oscillating charges in an antenna driven by an AC of the same frequency as the radio wave produced".

2. The Bidirectional Symmetry (HT)

Radio waves both are produced by AC andinduce AC when absorbed — both at the same frequency. Transmitter and receiver use the same physics, run in opposite directions.

3. The Ionising DNA Chain

For X-ray / gamma hazard questions, always run the full chain: ionising → damages DNA / mutates genes → cancer. For UV: damages skin cells → premature ageing AND increased skin cancer risk. Skipping the mechanism leaves the answer Level 1.

Summary

Producing EM Waves (HT — Spec 4.6.2.3)

Radio waves: oscillations in electrical circuits (alternating current in an antenna). Frequency of radio wave = frequency of AC.

Bidirectional: absorbed radio waves induce an AC in a circuit at the same frequency as the wave

UV / X-rays: changes in atoms (electron transitions between energy levels)

Gamma rays: changes in the nucleus of an atom (radioactive decay) — spec verbatim

The Ionising Boundary

Non-ionising: radio · microwave · infrared · visible — cannot strip electrons

Ionising: UV · X-rays · gamma — can strip electrons and damage DNA

Boundary sits between visible light and ultraviolet

Hazards — Mechanism & Mark-Scheme Language

Microwaves: heat tissue (water absorption)

Infrared: skin burns at high intensity

UV: "premature skin ageing" + "increased risk of skin cancer" (spec wording)

X-rays + gamma: "ionising radiation that can cause mutation of genes and cancer" (spec wording)

Radiation dose: measured in sieverts (Sv); 1000 mSv = 1 Sv; risk depends on TYPE and DOSE

The Single Biggest Habit

Every radio-production answer needs "alternating current" AND "same frequency as the AC". Every ionising-hazard answer needs "ionising → DNA / genes → cancer". Every safe answer about dose mentions "type AND size of dose". Three keywords. Three chains. Both halves of every two-point mark scheme.