Light: Mirrors and Lenses

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False (It is inverted.)

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False (They are made by grinding and polishing a flat glass piece.)

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False (It is seen in all three types of mirrors.)

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False (They are convex mirrors.)

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False (It is thicker at the edges.)

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False (A dentist uses a concave mirror.)

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False (It is measured between the reflected ray and the normal.)

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(d) (The laws are valid for all mirrors.)

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(d) (Lateral inversion is seen in all three types of mirrors.)

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(b) (A magnifying glass is a convex lens; R is true.)

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Hint: Mirror whose reflecting surface is spherical (part of an imaginary hollow sphere shape); types — concave and convex.

Hint: Concave — surface curves inwards; convex — surface curves outwards.

Hint: (i) Angle of incidence = angle of reflection; (ii) incident ray, normal at point of incidence, and reflected ray lie in the same plane.

Hint: Angle between normal and incident ray; angle between normal and reflected ray — both at the point of incidence.

Hint: r = 45° (i = r); angle with mirror surface = 90° − 45° = 45°.

Hint: i = 90° − 30° = 60°; r = 60°; angle between the two rays = 60° + 60° = 120°.

Hint: It converges the light into a strong parallel beam in the forward direction.

Hint: They give a wider field of view; drivers from both sides can see the traffic on the other side and avoid collisions.

Hint: Convex mirror forms diminished images, so vehicles appear smaller and hence look farther away than they really are.

Hint: Same size erect image → plane; enlarged erect image when close (inverted when far) → concave; always erect and diminished → convex.

Hint: Its surface is curved outward; the letters below appear enlarged, so it behaves like a simple convex lens.

Hint: Convex — thicker in middle, converges light; concave — thicker at edges, diverges light.

Hint: Convex lens; erect and enlarged view of the letters.

Hint: Ray retraces path along the normal; i = 0°, r = 0°.

Hint: Left-right interchange between object and image; e.g., the word 'AMBULANCE' written reversed so it reads correctly in the rear-view mirror of vehicles.

Hint: Image is inverted when close-at-hand distance; on moving away, the inverted image first enlarged then keeps getting smaller.

Hint: Reflected beam visible on flat extended sheet; disappears when sheet is bent — proving incident ray, normal, and reflected ray are in one plane.

Hint: Convex lens; it can change its shape to focus on near and far objects.

Hint: (i) They converge; (ii) they diverge.

Hint: It appears bent or changed in shape at the water surface; the curved surface of the water (acting like a lens) changes how the pencil appears.

Introduction: Spherical mirrors are curved mirrors shaped like a part of an imaginary hollow glass sphere.
Key Points:
1. Definition — Mirrors whose reflecting surfaces are spherical are called spherical mirrors, curved inward or outward.
2. Method of making — They are made by grinding and polishing a flat glass piece into a curved surface, not by slicing a sphere.
3. Two types — A reflective coating on the outer curved surface gives a concave mirror; coating on the inner curved surface gives a convex mirror.
Conclusion: Concave and convex mirrors are the two spherical mirrors, differing in the direction their surfaces curve.

Introduction: The nature of the image in a concave mirror depends on the distance of the object from it.
Key Points:
1. Object close to mirror — The image is erect and larger than the object, that is, enlarged.
2. Object moved away — The image becomes inverted, initially enlarged, and then keeps getting smaller.
3. Inversion and lateral inversion — Beyond a certain distance the image is inverted, while lateral inversion is seen at all distances.
Conclusion: Unlike a plane mirror, a concave mirror can form enlarged, diminished, or same-size images that may be erect or inverted.

Introduction: A convex mirror always gives the same type of image, whatever the object distance.
Key Points:
1. Nature of image — The image is always erect and smaller than the object, that is, diminished.
2. Effect of distance — As the object moves away, the image size decreases only slightly.
3. Difference from plane mirror — A plane mirror forms an image of the same size, while a convex mirror always forms a diminished image.
Conclusion: The always-erect, diminished image and the wider view make convex mirrors suitable for side-view mirrors.

Introduction: Reflection of light from any mirror is governed by two laws, valid for plane and spherical mirrors.
Key Points:
1. First law — The angle of incidence is equal to the angle of reflection (i = r).
2. Second law — The incident ray, the normal at the point of incidence, and the reflected ray all lie in the same plane.
3. Verification — Shine a narrow light beam on a plane mirror at different angles; measure i and r with a protractor each time; they are found equal.
Conclusion: Careful measurement in the slit-and-torch activity confirms that i always equals r.

Introduction: Concave mirrors are used in many devices because they converge light and form enlarged images of nearby objects.
Key Points:
1. Dental mirror — Held close to the teeth, it gives an enlarged view, helping the dentist inspect teeth.
2. Torch and headlight reflectors — The concave shape converges the light into a strong forward beam.
3. Reflecting telescopes — The main mirror of most modern telescopes is a large concave mirror.
Conclusion: These uses depend on the converging action and the enlarged image formed by concave mirrors.

Introduction: Convex mirrors are preferred wherever a wide field of view is needed.
Key Points:
1. Side-view mirrors — They form erect, diminished images of vehicles behind and cover a wider area.
2. Road safety mirrors — At intersections and sharp bends, they let drivers see traffic approaching from the other side.
3. Surveillance mirrors — Big stores install them to monitor large areas and deter thefts.
Conclusion: The wide view and always-erect image of convex mirrors help prevent accidents and thefts.

Introduction: Vehicle side-view mirrors use convex mirrors mainly for safety and a wider view.
Key Points:
1. Wide field of view — Since the convex mirror bulges outwards, it provides a much wider area of the road behind.
2. Erect image — It always forms an erect image of the traffic behind, which is easy for the driver to interpret.
3. Caution needed — The image is diminished, so vehicles look smaller and appear farther; hence the warning "Objects in mirror are closer than they appear."
Conclusion: A convex mirror gives safety through a wide view, but its small images make the caution necessary.

Introduction: The behaviour of parallel beams reveals the basic difference between concave and convex mirrors.
Key Points:
1. Setup — Obtain multiple parallel beams using a torch and a comb with several open slits.
2. Observation on plane mirror — The reflected beams remain parallel to one another.
3. Observation on spherical mirrors — On a concave mirror the beams come closer (converge); on a convex mirror they spread out (diverge).
Conclusion: Curved surfaces make parallel rays converge or diverge even though each ray obeys the laws of reflection.

Introduction: Solar concentrators are devices that concentrate sunlight into a small area using mirrors and lenses.
Key Points:
1. Activity — A concave mirror is held facing the Sun, and reflected light is directed onto a thin sheet of paper.
2. Bright spot — On adjusting the distance, a sharp bright spot forms where reflected sunlight gets concentrated.
3. Burning and uses — The heat produced can ignite the paper; concentrated sunlight is used for large-scale cooking, generating electricity, and solar furnaces that melt steel.
Conclusion: The converging property of a concave mirror can concentrate solar energy enough to produce intense heat.

Introduction: A lens is a piece of transparent material, usually glass or plastic, with curved surfaces.
Key Points:
1. Convex lens — It is thicker at the middle than at the edges and converges the light falling on it.
2. Concave lens — It is thicker at the edges than at the middle and diverges the light falling on it.
3. Seeing through lenses — Unlike mirrors, lenses let light pass through, so we see objects through them, not in them.
Conclusion: A convex lens is called a converging lens while a concave lens is called a diverging lens.

Introduction: Like a concave mirror, a convex lens forms different images at different object distances.
Key Points:
1. Object close to lens — The object appears erect and enlarged in size when seen through the lens.
2. Object moved away — The object appears inverted, initially enlarged, and then diminished in size.
3. Comparison — A concave lens, in contrast, always shows the object erect and diminished.
Conclusion: The image through a convex lens may be enlarged or diminished, erect or inverted, depending on distance.

Introduction: Lenses change the direction of parallel light beams passing through them.
Key Points:
1. Setup — Fix a thin glass plate, a convex lens, and a concave lens upright between two books; let multiple parallel beams fall on each.
2. Glass plate and convex lens — The beam passes through the glass plate unchanged, while the convex lens converges it.
3. Concave lens — The concave lens spreads the beam out, that is, diverges it.
Conclusion: Hence a convex lens is a converging lens and a concave lens is a diverging lens.

Introduction: Lenses are used in almost every optical device around us, including our own eyes.
Key Points:
1. Human eye — The eye contains a convex lens that can change its shape to see near and far objects clearly.
2. Common devices — Eyeglasses that people wear to see clearly, cameras including smartphone cameras, telescopes, and microscopes all use lenses.
3. Working together — Each device uses one or more lenses to bend light and form clear images.
Conclusion: From spectacles to space telescopes, lenses are essential for seeing and recording images.

Introduction: This numerical applies the first law of reflection and simple geometry.
Key Points:
1. Given — The incident ray makes 40° with the normal, so the angle of incidence i = 40°.
2. Law applied — By the first law of reflection, the angle of reflection r = i = 40°.
3. Angle with mirror — The angle made by the reflected ray with the mirror surface = 90° − 40° = 50°; diagram shows incident ray, normal, reflected ray with arrows.
Conclusion: The reflected ray leaves at 40° to the normal, which equals 50° to the mirror surface.

Introduction: The science-centre mirrors Meena saw were spherical mirrors of the two types.
Key Points:
1. Large face — Close to a concave mirror, the image is erect and enlarged, making her face look unusually large.
2. Upside-down brother — Standing farther from the same concave mirror, his image was inverted.
3. Tiny version — In a convex mirror, the image is always erect and diminished, giving a mini version.
Conclusion: A single concave mirror can give enlarged or inverted images by distance, while a convex mirror always diminishes.

Hint: (a) Concave mirror. (b) An object placed close to a concave mirror forms an erect, enlarged image. (c) On moving away, the image would no longer stay enlarged erect; it inverts and changes size. (d) Reflector of a torch / headlight / reflecting telescope.

Hint: (a) Convex mirror — erect images and a much wider field of view of both roads. (b) A concave mirror gives a narrow, inverted, or distorted image of distant objects. (c) Convex mirror, for a wider area of the road behind. (d) Convex mirrors always form diminished images.

Hint: (a) Inverted image of her face. (b) On the inner surface, the inverted image first enlarged and then kept getting smaller. (c) Erect but smaller (diminished) image. (d) The inner surface behaves like a concave mirror, the outer surface like a convex mirror.

Hint: (a) Reflected sunlight got concentrated at a point because the concave mirror converges light; heat produced ignited the paper. (b) No burning — a convex mirror diverges sunlight, so energy does not concentrate. (c) Solar cookers / solar furnaces / generating electricity by heating a liquid. (d) Never look at the Sun or into the mirror reflecting the Sun; focus light only on paper, not faces.

Hint: (a) Curved outward (bulging). (b) A simple lens — convex lens. (c) Magnifying glass. (d) The object appears inverted and its size diminishes as distance increases.

Hint: (a) r = 35° (since i = r). (b) 90° − 35° = 55°. (c) Both 0°. (d) First law — angle of incidence equals angle of reflection.

Hint: (a) Convex mirror. (b) It provides a wide field of view of a large area and always forms erect images. (c) Yes, lateral inversion is seen in all types of mirrors. (d) The office mirror is a plane mirror — same-size image but a much narrower field of view.

Hint: (a) Convex lens. (b) An object at a small distance from a convex lens appears erect and enlarged. (c) At larger distances the image through a convex lens becomes inverted and then diminishes. (d) A concave lens always gives an erect, diminished view at any distance.

Hint: (a) Concave mirror — it converges the beams. (b) Convex mirror — it diverges the beams. (c) No — every ray still obeys the laws of reflection; the curved surface only changes the normals. (d) Concave — torch reflector or solar cooker; convex — road-safety mirror or side-view mirror.

Hint: (a) Her inverted image keeps changing — first diminishing, then increasing in size, and eventually becoming erect and magnified as she comes close. (b) An erect, enlarged image of her face. (c) A convex (or plane) mirror — always erect. (d) The image of the right hand appears on the left side — left-right interchange occurs in all mirrors.

Introduction: Spherical mirrors are curved mirrors shaped like a part of an imaginary hollow glass sphere.
Key Points:
1. Meaning — Mirrors whose reflecting surfaces are spherical may curve inwards or outwards.
2. Manufacture — They are made by grinding and polishing a flat glass piece, then coating one curved side with a reflective layer like aluminium.
3. Concave mirror — Reflecting surface curves inwards; coating on the outer curved surface; converges light.
4. Concave images — Enlarged erect image of nearby objects; inverted image that shrinks as the object moves away.
5. Convex mirror — Surface curves outwards; coating on the inner curved surface; always erect, diminished image and diverges light.
Conclusion: The direction of curvature decides whether the mirror converges or diverges light and what image it forms.

Introduction: Reflection from any mirror, plane or spherical, follows two laws discovered through careful measurement.
Key Points:
1. First law — The angle of incidence is equal to the angle of reflection.
2. Verification of first law — A torch beam through a slit falls on a plane mirror at different angles; measuring i and r each time shows i = r.
3. Second law — The incident ray, the normal at the point of incidence, and the reflected ray lie in the same plane.
4. Verification of second law — When the extended chart paper sheet is bent, the reflected beam disappears; flattening it brings the beam back.
5. Numerical — If i = 40°, then r = 40°, and the reflected ray makes 90° − 40° = 50° with the mirror surface.
Conclusion: These two laws completely describe how light reflects from all mirrors.

Introduction: The nature of an image formed by a spherical mirror changes with the object's distance.
Key Points:
1. Setup — Place concave and convex mirrors upright side by side with a small object 3–4 cm in front.
2. Close object — Concave mirror gives an erect, enlarged image; convex mirror gives an erect, diminished image.
3. Object moved away — The concave image becomes inverted, first enlarged then smaller; the convex image decreases only slightly.
4. Lateral inversion — Lateral inversion is observed in the images formed by all three mirrors.
5. Conclusion of activity — Plane mirrors give same-size erect images, while spherical mirror images change with object distance.
Conclusion: Thus, spherical mirrors behave very differently from plane mirrors in image formation.

Introduction: The image-forming properties of spherical mirrors give them many practical uses.
Key Points:
1. Dentist's mirror — A concave mirror held close to the teeth forms an enlarged, erect image useful for inspection.
2. Torches and headlights — Concave reflectors converge light into a powerful parallel beam ahead.
3. Telescopes — Most modern reflecting telescopes use a large concave mirror as the main mirror.
4. Side-view mirrors — Convex mirrors give a wide view of the traffic behind with always-erect images.
5. Road and store safety — Convex mirrors at blind turns prevent collisions; in stores they monitor large areas to deter thefts.
Conclusion: Concave mirrors serve where convergence or magnification is needed; convex mirrors where a wide view matters.

Introduction: The behaviour of a parallel beam distinguishes the three kinds of mirrors.
Key Points:
1. Activity setup — Multiple parallel beams are made using a torch and a comb with several open slits.
2. Plane mirror — The reflected beams remain parallel to one another after reflection.
3. Concave mirror — The reflected beams get closer, that is, they converge, and can meet at a small bright spot.
4. Convex mirror — The reflected beams spread out, that is, they diverge.
5. Applications — Convergence by concave mirrors is used in solar cookers and furnaces; divergence by convex mirrors gives wide views in surveillance.
Conclusion: Every ray follows the laws of reflection, yet curvature makes the whole beam converge or diverge.

Introduction: A lens is a transparent piece of glass or plastic with curved surfaces that light can pass through.
Key Points:
1. Convex lens — It is thicker at the middle than at the edges and converges the light passing through it.
2. Concave lens — It is thicker at the edges than at the middle and diverges the light passing through it.
3. Activity — Parallel beams passed through a thin glass plate remain unchanged, through a convex lens they converge, through a concave lens they diverge.
4. Names — Hence the convex lens is called a converging lens and the concave lens a diverging lens.
5. Difference from mirrors — We see objects through a lens, whereas we see images in a mirror.
Conclusion: The shape of a lens decides whether it converges or diverges light.

Introduction: The two lenses form very different kinds of images of the same object.
Key Points:
1. Convex lens, object close — The object appears erect and enlarged in size.
2. Convex lens, object far — The object appears inverted, initially enlarged, and then diminishing.
3. Concave lens, any distance — The object always appears erect and diminished; size changes only slightly with distance.
4. Water-drop lens — A curved water drop acts like a convex lens and makes nearby letters appear enlarged.
5. Snapshots rule — A convex lens image may be enlarged, diminished, or same-size, erect or inverted; a concave lens image is always erect and diminished.
Conclusion: Object distance matters for a convex lens but hardly changes the always-small image of a concave lens.

Introduction: Lenses are used in almost every device that helps us see better or record images.
Key Points:
1. Human eye — The eye contains a convex lens that can change its shape, letting us read a book and see far away.
2. Eyeglasses — The spectacles people wear to see clearly use lenses.
3. Cameras — Cameras, including smartphone cameras, use lenses to form sharp pictures.
4. Scientific instruments — Telescopes and microscopes use lenses to magnify distant and tiny objects.
5. Magnifying glass — A convex lens used as a magnifying glass enlarges small print for easy reading.
Conclusion: From our eyes to space telescopes, lenses are essential tools for vision and imaging.

Introduction: The image of an object itself reveals the type of mirror or lens being used.
Key Points:
1. Plane mirror test — If the image is erect and exactly the same size as the object, the mirror is plane.
2. Concave mirror test — If the close-up image is erect and enlarged but becomes inverted when the object moves away, it is concave.
3. Convex mirror test — If the image is always erect and smaller than the object, the mirror is convex.
4. Graph-sheet check — The grid pattern also looks same-size in plane, enlarged or inverted in concave, and shrunken in convex mirrors.
5. Pencil in water — Viewed through water in a tumbler, a pencil looks bent or broken because the curved water surface acts like a lens.
Conclusion: Simple image observations are enough to classify any mirror or lens.

Introduction: A solar cooker uses the converging property of concave mirrors to trap solar energy as heat.
Key Points:
1. Principle — A concave mirror converges parallel sunrays to a small bright spot where heat concentrates.
2. Demonstration — In the activity, sunlight focused by a concave mirror on paper produced enough heat to ignite it.
3. Design — A large concave (or many small plane) mirrors focus sunlight onto a black cooking vessel kept at the bright spot.
4. Uses of concentrators — Solar concentrators heat liquids to produce steam for electricity, large-scale cooking, and solar furnaces.
5. Benefits — Such designs used in Indian villages save electricity and reduce fossil-fuel use and pollution.
Conclusion: A mirror-based solar cooker is a clean, low-cost application of the physics of curved mirrors.