NEB Class 12 • Physics • Physical Optics • Practice Set

Diffraction Practice Set: NEB 12 Physics

Master Diffraction through physical meaning, diagrams, a reliable answer method and exam-focused practice.

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Concepts · Worked reasoning · NEB practice

Quick answer: Diffraction is spreading and interference caused by a finite aperture or obstacle; it becomes prominent when aperture size is comparable with wavelength.

Worked practice

Build the result from meaning, not memory

Diffraction is spreading and interference caused by a finite aperture or obstacle; it becomes prominent when aperture size is comparable with wavelength.

Worked example

For λ=500 nm and a=0.20 mm, the first-minimum small angle is θ≈λ/a=2.5×10⁻³ rad.

The governing relationship is For a single slit, minima satisfy a sinθ=mλ, m=1,2,3…. The central maximum spans twice the angular width of a side maximum. Check the convention, geometry or boundary condition before calculation.

Independent practice ladder

  1. Define the key physical quantities and give their SI units.
  2. Draw and label the relevant wave, ray, mode or energy diagram.
  3. Recalculate the worked example after changing one input by a factor of two.
  4. Explain the result without equations.
  5. Create a Nepal-relevant situation such as a classroom speaker, musical pipe, optical slit or thermal machine.
  6. Compare two cases and predict the larger output before calculating.
  7. Find and repair one deliberately wrong sign, node or unit.
  8. Write a three-mark answer and a five-mark answer.

Answer protocol: diagram → known data → principle → symbolic equation → SI substitution → result → physical check. Calling diffraction simple refraction, using the double-slit formula for one slit, or drawing equal-width maxima.

NEB answer method

Diagram → principle → equation → check

First identify the physical system and what the question asks. Label the diagram with SI quantities, then write the principle in words before selecting a formula. Solve symbolically where possible and check dimensions, limiting cases and direction.

StageQuestion to askEvidence in answer
ModelWhat is idealised?Boundary or assumption stated
RepresentationWhich diagram fits?Labels, nodes, rays or energy arrows
CalculationWhich relation follows?Symbols then SI values
EvaluationDoes it make sense?Unit, sign and trend check

Make the idea concrete in Nepal

Connect the model to a school laboratory, musical instrument, auditorium, mobile communication, optical instrument or energy device. The example should clarify the physics rather than merely mention a place. For a visual experiment, use PhET Wave Interference and record which variable you changed and what observation followed.

Review the Class 12 Physics revision roadmap and the complete Physics guide. For online or physical tuition, call 9846662070.

Questions students ask about Diffraction

What is the central idea of Diffraction?

Diffraction is spreading and interference caused by a finite aperture or obstacle; it becomes prominent when aperture size is comparable with wavelength.

Which equation should I remember?

For a single slit, minima satisfy a sinθ=mλ, m=1,2,3…. The central maximum spans twice the angular width of a side maximum.

How should I begin a numerical?

Draw the situation, list known quantities in SI units, choose the governing relation symbolically, substitute once and finish with a unit and reasonableness check.

What is a common exam mistake?

Calling diffraction simple refraction, using the double-slit formula for one slit, or drawing equal-width maxima.

How can I practise this topic?

Alternate one concept explanation, one diagram and two numericals. Revisit errors after a day instead of only rereading the solution.

Where can I get tuition support?

For online or physical KTM Tuition classes, call 9846662070. After Grade 12, the MKS Education panel below gives preparation and pre-counselling contacts.

Frequently asked questions

References and next steps

Scope checked against CDC Nepal; concept support from OpenStax and PhET. Continue with the Diffraction cluster.

NEB +2 tuition support

Ask about online or physical tuition

For focused Class 11 and Class 12 subject tuition, lesson clarification, worked-example practice and exam preparation, call 9846662070. Class mode, timetable, teacher availability and fees should be confirmed directly before enrolment.

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