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CBSE Class 8 · Science

Light: Mirrors and Lenses

Official NCERT chapter from Curiosity (book code hecu1). ExamMaster notes are original teaching at CBSE Class 8 depth.

This lesson follows the official chapter “Light: Mirrors and Lenses” in Curiosity. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.

  • CBSE Class 8
  • Easy level
  • 8 concepts

1What Are Spherical Mirrors?

A spherical mirror is a piece of a hollow sphere’s shine: concave (inner shine) or convex (outer shine), as taught. It is not a plane mirror. The centre and the focus are named points you use later in the chapter; here, first see the bend of the surface.

A shiny spoon’s two sides are a kitchen look — still name concave versus convex.

Figure. A spherical mirror is a cut from a hollow sphere. This exam figure draws only the paraxial reflecting face — a short line — because a circle cannot be drawn here. Concave: F and C sit in front of P. Convex: F and C sit behind P. Hatch marks the silvered back.

How it works

  1. See the shine as part of a sphereSpherical.
  2. Inner shine → concave; outer → convexThe sort.
  3. Keep plane mirrors in last year’s drawer unless you need a contrastDifferent surface.

2What Are the Characteristics of Images Formed by Spherical Mirrors?

Images from spherical mirrors: a concave can make a real inverted image on a card (as demonstrated) or a magnified looking-image, depending on object distance as taught. A convex makes a smaller erect looking-image. Characteristics are size, erect/inverted, real/virtual as the lesson listed.

A plane-mirror “same size, behind” is not the concave-on-a-card look.

Figure. Concave mirror, object beyond C. A ray parallel to the axis reflects through F; a ray through F reflects parallel to the axis. They meet between C and F: real, inverted, diminished. Object height is twice image height, matching |v|/|u| = 15/30.

How it works

  1. Name concave or convexThe mirror.
  2. Name object-distance band if the lesson used oneNear, or farther.
  3. List size, erect or inverted, on-card or looking-onlyThe characteristics.

3What Are the Laws of Reflection?

Laws of reflection: the incoming ray, the normal, and the bounce sit in one plane, and the two angles with the normal match, as taught. A rough wall still reflects, but not as a single tidy pair you can mark. A plane or a small spherical patch can show the tidy pair.

A ray that “feels like it bounced anywhere” is not the law.

Figure. Law of reflection: the incident ray, the reflected ray, and the dashed normal lie in one plane, and i equals r. Drawn at 45 degrees from the normal so the two angles match on this 1.8-aspect frame.

How it works

  1. Draw the normal at the hit-pointThe reference.
  2. Mark i and rIncoming and bounce.
  3. See i = r in the same planeThe law.

4What Is a Lens?

A lens is a transparent piece that bends paths by its curved faces: convex (thicker middle) can meet rays to a real image on a card; concave (thinner middle) spreads them, as taught. A lens is not a spherical mirror — light goes through.

A bottle of water can act as a rough lens; it is a setting, not every law.

Figure. A lens is a transparent piece that bends rays. The diamond is the school symbol, not a drawn sphere. A ray arriving parallel to the axis leaves through F on the other side — that is what converging means here.

How it works

  1. See light through, not only bounceThe through-job.
  2. Thicker middle → convex; thinner middle → concaveThe sort.
  3. Try a card for a real image if the setup is convex as taughtA look.

5A definition is a test you can run

Lens and mirror words are tests: through versus bounce, and the surface-shape. If you cannot say through or bounce, you have a shiny object.

A name “lens” on a mirror is the swap.

Figure. A definition is a test you can run. Real image means a screen can catch it. Saying concave without running that test is a name, not the school check.

How it works

  1. Ask: through or bounce?The first test.
  2. Ask: spherical shine, or through-curve?The second.
  3. Then the word has contentThe definition ran.

6Name the given before the unknown

The given is the tool (concave mirror, convex lens…) and the object-distance if given. The unknown is the image-character. Copy which tool before you say “inverted on a card”.

A convex-mirror looking-image described as a concave-on-card image is a silent swap.

Figure. Name the given before the unknown. Mark object distance u and focal length f on the figure first. Image distance v is what you then find — it is not a free guess.

How it works

  1. Name the toolThe given.
  2. Name the image-list askedThe unknown.
  3. Use that tool’s taught listGiven first.

7One worked case is enough at this class

One card-image or one looking-image is enough. A page of the same spoon-clone does not add a new law of reflection.

Ten twins of one focus-word are still one idea.

Figure. One worked case: convex lens, object at 2F. A parallel ray goes through F; a ray through the centre goes straight. They meet at 2F on the other side — real, inverted, same size. That is enough at this class.

How it works

  1. Run one image-case or one i=r sketchThe case.
  2. A second only to contrast convex versus concaveOptional check.
  3. StopThis class.

8A miss: swapping the school name for the picture

A dentist-mirror photo is a setting. The science is concave-versus-convex and the image-list. A white coat and skipping the surface-sort is the swap-miss.

A clinic poster is not i = r.

Figure. The miss is swapping the school name for the picture. A box that only says CONCAVE teaches the word. The picture is the axis, the face, and two rays that actually meet.

How it works

  1. Keep the clinic as a storyA setting.
  2. Name the surface and the imageThe science.
  3. Point to through or bounceDo not swap.
A convex lens is
  1. Thicker in the middle — light goes through and can meet on a card
  2. A spherical mirror
  3. Always a looking-image only

Through, not bounce.

Notes

  • Mapped to the official NCERT chapter “Light: Mirrors and Lenses”. Original teaching only — no textbook sentences.
  • Science here is Physics, Chemistry and Biology ideas at this class, never a language or social-science chapter.

Recap

Hold these pegs from the official chapter “Light: Mirrors and Lenses”. The wording is ExamMaster’s teaching, not a textbook recap.

What Are Spherical Mirrors?
A spherical mirror is a piece of a hollow sphere’s shine: concave (inner shine) or convex (outer shine), as taught.
What Are the Characteristics of Images Formed by Spherical Mirrors?
Images from spherical mirrors: a concave can make a real inverted image on a card (as demonstrated) or a magnified looking-image, depending on object distance as taught.
What Are the Laws of Reflection?
Laws of reflection: the incoming ray, the normal, and the bounce sit in one plane, and the two angles with the normal match, as taught.
What Is a Lens?
A lens is a transparent piece that bends paths by its curved faces: convex (thicker middle) can meet rays to a real image on a card; concave (thinner middle) spreads them, as taught.
A definition is a test you can run
Lens and mirror words are tests: through versus bounce, and the surface-shape.
Name the given before the unknown
The given is the tool (concave mirror, convex lens…) and the object-distance if given.

Practise Light: Mirrors and Lenses

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