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Wave Optics — NEET & JEE Physics MCQs

30 questions written by hand against the NCERT chapter. Every wrong option is explained, not just the right one.

30questions
10/14/6easy / medium / hard
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Sample questions from this chapter

What is a wavefront?
  1. A surface of constant phase ✓
  2. The path followed by one photon
  3. A surface of constant intensity only
  4. The line joining a source to an observer
Answer: A. A wavefront is the locus of points oscillating with the same phase; energy propagates normal to it.
Why not B: A ray describes propagation direction, whereas a wavefront contains many in-phase points.
Why not C: Equal amplitude may occur on ideal spherical fronts, but phase defines a wavefront.
Why not D: A source-observer line is a ray normal to the wavefront, not the front itself.
An entire Young double-slit apparatus is immersed in a liquid of refractive index n without changing its geometry. How does fringe width change?
  1. It becomes nβ because d decreases
  2. It remains β because frequency is unchanged
  3. It becomes β/n because wavelength decreases ✓
  4. It becomes β/n² because both λ and d decrease
Answer: C. In the liquid λ′=λ/n while D and d stay fixed, so β′=λ′D/d=β/n.
Why not A: The physical slit separation does not contract on immersion, and wavelength decreases.
Why not B: Frequency stays fixed, but the reduced speed lowers wavelength and fringe width.
Why not D: Only optical wavelength changes; d is a geometric distance.
In a Young experiment, d=0.280 mm and D=1.40 m. The fourth bright fringe is 1.20 cm from the central maximum. What wavelength is used?
  1. 600 nm ✓
  2. 800 nm
  3. 480 nm
  4. 1200 nm
Answer: A. x₄=4λD/d, so λ=xd/(4D)=(0.0120)(2.80×10⁻⁴)/(4×1.40)=600 nm.
Why not B: This calls the central maximum the first bright fringe and therefore uses order n=3.
Why not C: This uses five fringe intervals between the centre and fourth bright fringe.
Why not D: This uses only two intervals and overestimates wavelength by two.

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Every NCERT question in this chapter is solved, free: NCERT solutions — Wave Optics →

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Questions

How many NEET and JEE questions are there on Wave Optics?

This chapter test has 30 questions — 10 easy, 14 medium and 6 hard — all written against the NCERT Class 12 chapter.

Is this NEET and JEE Physics chapter test free?

Yes. Every chapter test is free with no login, and you get your all-India rank on every one. Nothing on the site is on sale right now.

Do the questions explain the wrong options?

Yes — every distractor carries its own explanation naming the specific misconception that makes a student pick it. That is the part most question banks skip, and it is the part that changes your next attempt.