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Wave Optics

NCERT Class 12 Physics Chapter 10

Wave Optics for Class 12 Physics, JEE and NEET: Huygens principle, Young’s experiment, single-slit diffraction and polarisation, with solved examples.

7 topics Updated 8 Nov 2026

For: Class 12, JEE and NEET, unless a topic says otherwise

In the syllabus: JEE Class 12 syllabus, NEET Class 12 syllabus

With your textbook

NCERT Physics Part II (Class 12), Chapter 10 “Wave Optics”, reprint 2026-27.

Open the official NCERT chapter (PDF, 2.7 MB, ncert.nic.in)

Checked on 19 Oct 2026.

Learn in this order

  1. Huygens principle and wavefronts

    Wavefronts and rays, spherical and plane waves, secondary wavelets, the missing backwave, solved examples.

    NCERT Sections 10.1–10.2 12 min read 4 solved examples 7 practice questions

  2. Refraction and reflection by Huygens principle

    Snell’s law from wavefronts, i = r in reflection, wavelength and frequency, solved examples.

    NCERT Section 10.3 14 min read 4 solved examples 7 practice questions

  3. Coherent and incoherent addition of waves

    Sustained interference, path and phase difference, I = 4I cos(φ/2), solved examples.

    NCERT Section 10.4 12 min read 4 solved examples 7 practice questions

  4. Young’s double-slit experiment

    Set-up, path difference xd/D, bright and dark fringes, fringe width β = λD/d, solved examples.

    NCERT Section 10.5 13 min read 4 solved examples 7 practice questions

  5. Diffraction at a single slit

    The single-slit pattern, minima at θ ≈ nλ/a, central maximum width 2λ/a, interference vs diffraction.

    NCERT Section 10.6 16 min read 4 solved examples 7 practice questions

  6. Polarisation of light

    Plane-polarised and unpolarised light, polaroids, Malus’ law I = I cosθ, uses and solved examples.

    NCERT Section 10.7 13 min read 4 solved examples 7 practice questions

  7. Brewster’s law

    Polarisation by reflection, the Brewster or polarising angle from tan iB = μ, rays at right angles, solved examples.

    JEE and NEET only 11 min read 4 solved examples 10 practice questions

Key formulas in this chapter

Huygens principle

  • R = R0 + vτ
  • v = c/n
  • I = P/(4πr2)

Refraction and reflection by Huygens principle

  • sin i/sin r = v1/v2
  • n = c/v
  • n1 sin i = n2 sin r
  • λ1/λ2 = v1/v2
  • sin ic = n2/n1

Coherent and incoherent addition

  • φ = (2π/λ)Δ
  • I = 4I0 cos2(φ/2)
  • I = 2I0 (incoherent)
  • I = I1 + I2 + 2√(I1 I2) cos φ

Young’s double-slit experiment

  • path difference = xd/D
  • xn = nλD/d (bright)
  • xn = (n + 1/2)λD/d (dark)
  • β = λD/d

Diffraction

  • a sin θ = nλ (nonzero orders)
  • θn ≈ nλ/a (small-angle minima)
  • angular width = 2λ/a
  • linear width = 2λD/a

Polarisation

  • I = Iu/2 (unpolarised, one polaroid)
  • I = I0 cos2 θ
  • I = (I0/4) sin2 2θ (polaroid between crossed polaroids)

Brewster’s law

  • tan iB = μ
  • iB + r = 90°

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