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UPPCS Physics Gap Sheet: Mirrors, Lenses and Vision.
UPPCS has asked 26 of these. 4 have not been asked yet. Lock the first list, then read the second: it holds what UPPCS has not used yet.
First, the concept
A real image can be formed on a screen; a virtual image cannot. Converging mirrors and lenses can form different images as object distance changes. Diverging ones normally give upright, smaller virtual images of real objects.
The eye focuses light on the retina by changing lens curvature. Vision defects arise when focus falls before or behind the retina, or differs by direction. A correcting lens changes the incoming convergence so that focus returns to the retina.
✅ Already asked (26)
Mirrors
- Plane-mirror image · Virtual, upright and the same size as the object; it shows lateral inversion.
- Full-length plane mirror · Its minimum height is half the person's height when placed correctly.
- Parallel plane mirrors · Ideal parallel mirrors can produce infinitely many images.
- Plane-mirror curvature · Its radius of curvature is infinite.
- Convex rear-view mirror · A wide field of view and smaller upright images help drivers.
- Dentist's concave mirror · A nearby tooth within the focus gives an upright magnified virtual image.
- Concave searchlight mirror · A source at the focus gives a nearly parallel outgoing beam.
Lenses and optical instruments
- Convex lens in air · Usually converges rays; within its focal length it acts as a magnifying glass.
- Concave lens in air · Diverges rays and gives an upright diminished virtual image of a real object.
- Air bubble in water · Acts as a diverging lens because air has a lower refractive index than water.
- Dioptre · Unit of lens power; a shorter focal length means greater magnitude of power.
- Astronomical telescope · In normal adjustment, the final image is virtual, magnified and inverted.
- Compound microscope · The objective forms a magnified real intermediate image; the eyepiece magnifies it further.
Eye and defects
- Retinal image · A real, inverted image forms on the retina; the brain interprets visual signals.
- Accommodation · Ciliary muscles change lens curvature to focus at different distances.
- Normal near point · For a young normal eye, the least distance of clear vision is about 25 cm.
- Myopia · Distant objects blur; their focus lies in front of the retina; a concave lens corrects it.
- Hypermetropia · Near objects blur; their focus would lie behind the retina; a convex lens corrects it.
- Astigmatism · Unequal focusing in different directions is commonly corrected with a cylindrical lens.
- Daylight sensitivity · Human photopic vision is most sensitive near 555 nm, in yellow-green light.
Further vision and imaging
- Cornea's role · The air-cornea surface provides most of the eye's refraction; the lens fine-tunes focus.
- Iris and pupil · The iris controls pupil size to regulate incoming light.
- Rods and cones · Rods support dim-light vision; cones support colour vision in brighter light.
- Blind spot · Where the optic nerve leaves the retina, there are no photoreceptors.
- Cataract · Clouding of the eye's lens scatters light and impairs vision.
- Colour blindness · Often results from missing or altered cone photopigments; it is not ordinary myopia.
❌ Not asked yet (4)
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🔒 4 items not asked yet
Lenses and optical instruments: 1 · Eye and defects: 1 · Further vision and imaging: 2
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⚠️ A convex mirror diverges light; a convex glass lens in air converges it. Myopia needs a concave lens; hypermetropia needs a convex lens.
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