The shape of the lesson
By the end of the lesson, learners can
- Send radiation at living tissue: Choose a band and watch how it interacts with cells, gently for low frequencies and damagingly for the high frequency end.
- Higher frequency, greater danger: Each region affects the body differently, and the harm grows toward the high frequency end of the spectrum.
- Lower frequency (microwave, infrared): the main effect is heating of tissue.
- Higher frequency (ultraviolet, X-ray, gamma): enough energy to damage or mutate cells, causing cancer.
- Protection means reducing exposure: shielding, distance, limiting dose and time, and covering up.
One picture every idea returns to
The danger of an electromagnetic wave rises with its frequency, because higher frequency waves carry more energy. Microwaves heat the water in cells, infrared burns skin, and ultraviolet, X-rays and gamma rays are energetic enough to damage or mutate living cells.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, When energy does harm.. The same spectrum that warms your skin and shows you the world can also burn, blind, and trigger cancer. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Send radiation at living tissue | Choose a band and watch how it interacts with cells, gently for low frequencies and damagingly for the high frequency end. Project tab 2 of the lab (Harmful effects) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Higher frequency, greater danger | Each region affects the body differently, and the harm grows toward the high frequency end of the spectrum. | Think-Pair-Share |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 14 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Higher frequency, greater danger, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Think-Pair-Share
Pose the question, give thirty seconds of silent thinking, then a minute to compare with a partner before a few pairs share with the class. The silent minute is the part that cannot be cut.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| It is the high frequency end of the spectrum, ultraviolet, X-rays and gamma rays, that is the most dangerous, because the energy carried rises with frequency. | Microwaves do not scorch like a flame; they heat the water inside cells from within. |
Harmful effects of EM radiation: worksheet
6 questions, 14 marks. Written in the style of the papers; no past paper question is reproduced.
State a harmful effect on the body of:
(a) microwaves, [1] (b) infrared. [1]Sunlight contains ultraviolet radiation.
(a) State two harmful effects of ultraviolet on the body. [2] (b) State one way a person can reduce their exposure to ultraviolet. [1]State the main harmful effect of X-rays and gamma rays on the cells of the body.
Explain why, in general, the radiations at the high-frequency end of the electromagnetic spectrum are more harmful to the body than those at the low-frequency end.
A student claims that microwaves are dangerous in the same way as gamma rays, because both are "radiation". Explain why this comparison is misleading.
A radiographer takes many X-ray images each day.
(a) Explain why repeated exposure to X-rays is a risk to the radiographer. [1] (b) State two precautions the radiographer can take to reduce their exposure. [2]Answer key and marking notes
(a) Internal heating of body cells (microwaves are absorbed by water in the tissue). ✓
(b) Skin burns from heating. ✓
(a) Any two of: sunburn, premature ageing of the skin, skin cancer, eye damage. ✓✓
(b) Any one of: sunscreen, sunglasses, covering clothing, or limiting time in strong sun. ✓
- They can damage or mutate cells (including their DNA). ✓
- This can cause cancer, and high doses can kill cells. ✓
- Higher frequency means each wave carries more energy. ✓
- That energy is enough to damage or mutate the molecules in cells, rather than just heating the tissue. ✓
- Microwaves have a much lower frequency and energy, so their main effect is heating tissue, not damaging cells. ✓
- Gamma rays carry far more energy and can mutate or destroy cells, causing cancer, which microwaves do not do. ✓
(a) X-rays can damage or mutate cells, and repeated exposure increases the total dose and so the risk of cancer. ✓
(b) Any two of: stand behind a lead or concrete screen, wear a lead apron, keep their distance, limit exposure time, and wear a badge to monitor their dose. ✓✓
1 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Excessive exposure to which type of electromagnetic radiation is most strongly linked to skin cancer and sunburn?
- Aultraviolet
- Bradio waves
- Cinfrared
- Dmicrowaves
Quiz key
Ultraviolet radiation damages skin cells and can cause sunburn and skin cancer. Radio waves, infrared and microwaves are lower in energy and do not cause this kind of cell damage in the same way.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.