Prostuti360°Prostuti360°
Log in

WBCS Preliminary Examination 2021 — General Studies · Question 50 of 200

Q50
General SciencePhysics
The spectrum of color in Compact Disc (CD) is due to
  1. a.Refraction
  2. b.Reflection
  3. c.Diffraction
  4. d.Polarization

Answer: (C) Diffraction

The closely spaced spiral tracks on a CD (about $1.6\,\mu m$ apart) act as a reflection diffraction grating: white light diffracted from neighbouring tracks interferes, and different wavelengths are reinforced at different angles, producing rainbow colours. Refraction (bending on entering another medium) gives the spectrum of a prism or a rainbow, plain reflection does not separate colours, and polarisation restricts the plane of vibration (used in sunglasses and LCDs). The colours of soap bubbles and oil films, by contrast, come from thin-film interference.

Q49 Whole paperQ51