The shape of the lesson
By the end of the lesson, learners can
- Move the focus back to the retina: Switch between a short-sighted and long-sighted eye, then add the correcting lens and watch the image sharpen.
- Two faults, two lenses: Each defect focuses the image in the wrong place, and each is corrected by the opposite type of lens.
- Short sight: distant blurred, focus in front of the retina, corrected with a diverging lens.
- Long sight: near blurred, focus behind the retina, corrected with a converging lens.
- Cause: short sight, eyeball too long or lens too strong. Long sight, eyeball too short or lens too weak.
One picture every idea returns to
In short sight, distant objects focus in front of the retina and are corrected with a concave (diverging) lens. In long sight, near objects focus behind the retina and are corrected with a convex (converging) lens.
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, Back onto the retina.. A healthy eye lands a sharp image right on the retina. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Move the focus back to the retina | Switch between a short-sighted and long-sighted eye, then add the correcting lens and watch the image sharpen. Project tab 7 of the lab (Correcting sight) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Two faults, two lenses | Each defect focuses the image in the wrong place, and each is corrected by the opposite type of lens. | 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, 16 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 Two faults, two lenses, 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 |
|---|---|
| Short sight is corrected with a concave (diverging) lens, not a converging one, and long sight with a convex (converging) lens. | Pairing the defect with the wrong lens is the classic mistake here. |
Correcting short and long sight: worksheet
6 questions, 16 marks. Written in the style of the papers; no past paper question is reproduced.
A person is short-sighted.
(a) State whether they see near or distant objects clearly. [1] (b) State where light from a distant object is focused relative to the retina. [1] (c) Name the type of lens used to correct it. [1]A person is long-sighted.
(a) State whether they see near or distant objects clearly. [1] (b) State where light from a near object is focused relative to the retina. [1] (c) Name the type of lens used to correct it. [1]Explain, in terms of the shape of the eyeball or the strength of the eye lens, two possible causes of short sight.
The diagram shows parallel light from a distant object entering an eye.
A student writes that long sight is corrected with a diverging lens. Explain why this is wrong, and give the correct lens with a reason.
An elderly reader finds they have to hold a newspaper at arm's length to read it clearly, but they can see across the street without difficulty.
(a) Name the sight defect. [1] (b) Explain, in terms of the focus, why the newspaper is blurred when held close. [1] (c) State the lens that would correct it. [1]Answer key and marking notes
(a) Near objects clearly; distant objects are blurred. ✓
(b) The light focuses in front of the retina. ✓
(c) A diverging (concave) lens. ✓
(a) Distant objects clearly; near objects are blurred. ✓
(b) The light would focus behind the retina. ✓
(c) A converging (convex) lens. ✓
- The eyeball is too long, so the retina is further back than the focus point. ✓
- The eye lens is too strong (too powerful), so it bends the light too much and focuses it too soon. ✓
(a) Short sight. ✓
(b) The light is focused in front of the retina, so the image on the retina is blurred. ✓
(c) A diverging (concave) lens. ✓
- In long sight the light focuses behind the retina, so a lens that spreads light out further would only make it worse. ✓
- A converging lens is needed, because it brings the light together sooner so it focuses on the retina. ✓
(a) Long sight. ✓
(b) Light from the close newspaper is focused behind the retina, so its image on the retina is not sharp. ✓
(c) A converging (convex) lens. ✓
Holding it at arm's length pushes the object far enough that the eye can just focus it. The convex lens removes the need.
3 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.
A short-sighted person cannot focus on distant objects because the image forms in front of the retina. Which lens corrects this?
- Aa diverging (concave) lens
- Ba converging (convex) lens
- Ca flat glass plate
- Dno lens can correct it
A long-sighted person cannot focus on near objects because the image would form behind the retina. Which lens corrects this?
- Aa converging (convex) lens
- Ba diverging (concave) lens
- Ca coloured filter
- Da plane mirror
Which defect of vision is corrected using a diverging lens?
- Ashort sight (myopia)
- Blong sight (hyperopia)
- Ccolour blindness
- Da damaged retina
Quiz key
Short sight is corrected with a diverging (concave) lens, which spreads the light out a little so the image forms further back, on the retina. A converging lens would make the problem worse.
Long sight is corrected with a converging (convex) lens, which bends the rays inward more so the image forms on the retina rather than behind it. A diverging lens would worsen it.
Short sight (myopia) is corrected with a diverging lens, because the eye focuses light too soon. Long sight needs a converging lens, the opposite case.
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.