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Geometrical Optics question

2023 · 11 Apr · Shift 2 · Q49
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  5. /2023 · 11 Apr · Shift 2 · Q49

Geometrical Optics question

2023 · 11 Apr · Shift 2 · Q49

JEE MainPhysicsGeometrical OpticsMCQ+4 / −1
When one light ray is reflected from a plane mirror with 30∘30^{\circ}30∘ angle of reflection, the angle of deviation of the ray after reflection is :
  1. A
    140∘140^{\circ}140∘
  2. B
    130∘130^{\circ}130∘
  3. C
    120∘120^{\circ}120∘
  4. D
    110∘110^{\circ}110∘
View written solutionFree

Correct answer: C

  1. Given:

    • Angle of reflection, r=30∘r = 30^\circr=30∘
    • For a plane mirror, angle of incidence equals angle of reflection: i=r=30∘i = r = 30^\circi=r=30∘

  2. Angle between incident ray and reflected ray: In reflection from a plane mirror, the incident and reflected rays make equal angles with the normal. So the angle between them is: i+r=30∘+30∘=60∘i + r = 30^\circ + 30^\circ = 60^\circi+r=30∘+30∘=60∘

  3. Angle of deviation: The angle of deviation is the angle through which the ray is turned from its original path. For reflection at a plane mirror, δ=180∘−(i+r)\delta = 180^\circ - (i + r)δ=180∘−(i+r) Since i=ri=ri=r, δ=180∘−2i\delta = 180^\circ - 2iδ=180∘−2i δ=180∘−2(30∘)=180∘−60∘=120∘\delta = 180^\circ - 2(30^\circ) = 180^\circ - 60^\circ = 120^\circδ=180∘−2(30∘)=180∘−60∘=120∘

  4. Check options:

    • A: 140∘140^\circ140∘ ❌
    • B: 130∘130^\circ130∘ ❌
    • C: 120∘120^\circ120∘ ✅
    • D: 110∘110^\circ110∘ ❌

Therefore, the correct answer is Option C.

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