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CBSE Class 10 · Science

Light – Reflection and Refraction

Official NCERT chapter from Science (book code jesc1). ExamMaster notes are original teaching at CBSE Class 10 depth.

This lesson follows the official chapter “Light – Reflection and Refraction” in Science. 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 10
  • Medium level
  • 8 concepts

1REFLECTION OF LIGHT

Reflection: the bounce from a surface you can name. Angle of incidence equals angle of reflection, both from the normal (as taught). A mirror-look is this heading; a wall-scatter can still be a bounce-story if the lesson used it. Reflection is i = r, not “it bounced somehow”.

Measuring from the surface instead of the normal is a miss if the lesson used the normal.

Figure. A vertical plane mirror facing left. The dashed normal is perpendicular to the glass. Incident and reflected rays sit on opposite sides of that normal and make the same 21.8° opening — i equals r. Angles are true in this aspect: each opening has visual rise 0.32 on a visual run of 0.80.

How it works

  1. Draw the normalThe perpendicular.
  2. Mark i and r from that normalThe two angles.
  3. Set i = rThe law.

2SPHERICAL MIRRORS

Spherical mirrors are a slice of a sphere: concave caves in, convex bulges out, as taught. A ray-sketch (parallel to axis through the focus, as the lesson drew) is the method. Real versus virtual is a screen-or-not story. One object-distance case is enough.

A spoon-photo without a ray is a setting.

Figure. The reflecting surface is the thin-mirror cut, not a drawn sphere. F sits halfway from pole P to centre C. A ray parallel to the axis returns through F; a ray through C returns on itself. They meet at a real inverted image half as tall: u = 2f and v = f give m = −v/u = −1/2. Image height 0.11 against object height 0.22.

How it works

  1. Name concave or convexThe shape.
  2. Draw the taught raysThe sketch.
  3. Name the image as the lesson did (real/virtual, inverted/upright)The image.

3REFRACTION OF LIGHT

Refraction is the bend when light changes medium: air to glass, air to water, as taught. Toward the normal into a denser school-medium, away when leaving — if that is the lesson’s rule. Refraction is the bend, not a second reflection.

A broken-pencil photo is a setting until the two media are named.

Figure. Air into glass of refractive index 1.5. Snell: sin 36° / sin r = 1.5 gives r = 23°. The refracted ray lies closer to the dashed normal than the incident ray. Angles are true in this 1.6 aspect: each uses dy = aspect · tan(angle) · dx.

How it works

  1. Name the two mediaThe change.
  2. Draw the ray bending at the surfaceThe refraction.
  3. Use toward/away as taughtThe rule.

4A definition is a test you can run

Reflection / refraction is a test: i = r, or a named bend at a medium-change. If you only say “light”, you have a heading.

A sun-glare selfie is not the test.

Figure. The definition of reflection is a test: measure the opening from the dashed normal to each ray. The pair is a reflection only when those two openings match. The figure uses the same 21.8° geometry as the first concept.

How it works

  1. Name bounce-with-law or bend-at-a-changeThe object.
  2. Give the school sentenceThe test.
  3. Then the word has contentThe definition ran.

5Name the given before the unknown

The given is the mirror-type or the two media. The unknown is the image or the bend-way. Copy “concave” before you draw a convex bulge.

A decorative spoon is not the given ray-box.

Figure. Name the given before the unknown. The object distance u and the focal length f are marked first. The image distance v is what the mirror formula then answers — it is not a third guess on the axis.

How it works

  1. Copy the shape or the mediaThe given.
  2. Name image or bendThe unknown.
  3. Then sketchGiven first.

6One worked case is enough at this class

One ray-sketch is enough. A page of the same i = r clone does not add a new concave case.

Ten twins of a spoon are still one setting.

Figure. One worked case at this class: object at C, which is 2F. The parallel ray returns through F and meets the axis again at C. The image is real, inverted, and the same height — m = −v/u = −1. Object and image heights are both 0.22 on the page.

How it works

  1. Run one bounce or one bendThe case.
  2. A second only as a checkOptional.
  3. StopThis class.

7A miss: swapping the school name for the picture

A lake-photo is a setting. The science is i = r or a named bend. Sparkle is not the law.

A sunset still is not refraction until two media are named.

Figure. The miss is swapping the school name for the picture. A plane-mirror bounce is the i = r test. Labelling that same bounce F pretends the surface is spherical. F is a mark on the axis of a curved mirror, not a name for any reflected ray.

How it works

  1. Keep the lake as a storyA setting.
  2. Draw normal and i, r, or the two mediaThe science.
  3. Then the law or the bendDo not swap.

8Check by the opposite action or the opposite test

Check i = r by measuring from the normal both sides; check a bend by swapping the media (the ray should reverse the toward/away, as taught). A sketch that never marked the normal fails the opposite test.

A “looks bent” without two media is not a check.

Figure. Check by the opposite action. Send a ray back along the reflected path and it retraces the incident path. The openings about the dashed normal stay 21.8°. Reversibility is the opposite test of i = r, not a new law.

How it works

  1. State i = r or toward-the-normalThe claim.
  2. Rebuild from the normal or swap mediaThe check.
  3. Mend if they disagreeHonest.
i and r are measured from
  1. The normal — and they are equal in reflection
  2. The surface always, and they need not match
  3. The focus

The law needs the normal.

Notes

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

Formulas

  • reflection: i = r (from the normal)

Recap

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

REFLECTION OF LIGHT
Reflection: the bounce from a surface you can name.
SPHERICAL MIRRORS
Spherical mirrors are a slice of a sphere: concave caves in, convex bulges out, as taught.
REFRACTION OF LIGHT
Refraction is the bend when light changes medium: air to glass, air to water, as taught.
A definition is a test you can run
Reflection / refraction is a test: i = r, or a named bend at a medium-change.
Name the given before the unknown
The given is the mirror-type or the two media.
One worked case is enough at this class
One ray-sketch is enough. A page of the same i = r clone does not add a new concave case.

Practise Light – Reflection and Refraction

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  • A 4-question practice set that ends the chapter
  • 1 quick check with worked explanations
  • Timed mocks scored with the real marking scheme
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