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Playbook

Modern Physics

25 q · 0% HARD. Atomic structure, nuclear fission/fusion, photoelectric effect (qualitative), E=hf dimension, scientist–discovery pairs, acronyms (LED, LASER). Every question is recall.

questions in the bank
25
tagged HARD
0%
subtopic(s)
6
worked examples
2

When you’ll see it

An atomic-structure recall (electron/proton/neutron mass), a nuclear fission/fusion statement, a photoelectric phrase, a scientist–discovery pair, or an LED/LASER acronym.

How this chapter is tested

25 q across 10 years, ZERO HARD. The chapter rewards memorisation discipline more than any other in NDA Physics. The work is flashcard-style: scientist pairs, acronyms, and the three-tier atomic model history (Dalton → Thomson plum-pudding → Rutherford nuclear → Bohr quantised orbits).

Photoelectric effect tests its qualitative shape, not its math: light KICKS electrons from a metal surface, threshold frequency below which nothing happens regardless of intensity, KE depends on frequency above threshold. E = hf is the only formula and it's tested via dimensions ('what are the dimensions of Planck's constant?') more than plug-in.

Nuclear physics is statement-truth: fission (heavy splits) powers reactors and bombs; fusion (light combines) powers the sun and hydrogen bombs. The 'binding energy per nucleon' curve peaks around iron-56 — heavier-than-iron fuses release energy, lighter-than-iron split releases.

The sub-skills

The rules and habits that decide whether you get a question right.

  • Scientist → discovery pairing

    8 canonical pairs cold: Chadwick=neutron, Einstein=photoelectric, Marie Curie=radium/polonium, Rutherford=nuclear, Bohr=atomic, Planck=quantum, J.J. Thomson=electron, Roentgen=X-rays.

  • Acronym expansion

    LED = Light Emitting Diode. LASER = Light Amplification by Stimulated Emission of Radiation. MASER = Microwave. NMR = Nuclear Magnetic Resonance. MRI = Magnetic Resonance Imaging.

  • Atomic model history

    Dalton (indivisible atom) → Thomson (plum pudding) → Rutherford (gold-foil ⟹ small dense nucleus) → Bohr (quantised orbits) → quantum mechanics (probability clouds).

  • Fission vs fusion

    Fission = heavy nucleus splits (U-235 in reactors, atom bomb). Fusion = light nuclei combine (sun, hydrogen bomb). Both release energy because of binding-energy-per-nucleon shape.

2 worked examples from the bank

Real past-year questions illustrating the playbook. Click to reveal options + solution.

Example 1Modern PhysicsMODERATE
The energy E of a photon can be expressed as E = hf where f is the frequency and h is Planck's constant. The dimensions of h are the same as that of

[Q60 · Sep · 2025]

Example 2Modern PhysicsMODERATE
Which of the following pairs of physical phenomenon and the discoverer is/are correctly matched ? 1. James Chadwick : Photoelectric effect 2. Albert Einstein : Neutron 3. Marie Curie : Radium Select the correct answer using the code given below :

[Q53 · Apr · 2021]

Traps to expect

Distractor shapes specific to this chapter. The page-wide Traps section covers the bank-level patterns.

  • Photoelectric — intensity vs frequency

    Intensity below threshold frequency does NOTHING. Above threshold, intensity controls number of electrons, frequency controls their KE. The wrong option swaps these.

  • X-rays vs gamma rays

    Both EM radiation. X-rays come from atomic transitions (electron shells); gamma from nuclear transitions. Common trap: 'X-rays come from the nucleus.'

Drill every modern physics question

25 questions from the bank, scoped to 6 bundled subtopics.

Drill the 25 questions

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