Practise 47 real Federal Board questions on Dawn of Modern Physics from 2023 to 2026. See the answer and explanation as soon as you answer.
Dawn of Modern Physics is one of the 14 main chapters in our Federal Board FSC Physics question bank (11th and 12th class), and about 9% of its real questions come from it. Tayyari Karo has 47 real questions on this chapter from 2023 to 2026; 17 are multiple choice and marked instantly, and the rest are short and long questions with a model answer. By difficulty: 35 medium, 7 hard, 5 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
Postulates of special theory of relativity applies to:
Answer: C. All physical laws
Einstein's first postulate states the laws of physics are the same (invariant) in all inertial frames of reference — it applies to all physical laws, not just optics.
Proton is made up of:
Answer: B. 1 down and 2 up quarks
A proton consists of 2 up quarks and 1 down quark (charge = 2/3+2/3−1/3 = +1).
When an object moves with a very high speed in the direction of its length, its length ________.
Answer: A. Contracts
By special relativity, length contraction: L = L₀√(1−v²/c²) < L₀ along the direction of motion.
Which is NOT the characteristic of LASER?
Answer: B. Multi-directional
Laser light is highly directional (a narrow, non-spreading beam), not multi-directional.
At what speed does the mass of a body become double its proper (rest) mass?
Answer: B. √3/2 c
m = m₀/√(1−v²/c²) = 2m₀ ⟹ √(1−v²/c²) = 1/2 ⟹ v²/c² = 3/4 ⟹ v = (√3/2)c.
If the velocity of a free electron is doubled, its De-Broglie wave length changes by the factor of:
Answer: B. 1/2
λ = h/(mv), so λ is inversely proportional to v. Doubling v halves λ (factor of 1/2).
Describe photon as a force carrier.
In quantum field theory, the electromagnetic force between charged particles is understood as being 'carried' or mediated by the exchange of photons — virtual particles of the electromagnetic field. When two charged particles interact (attract or repel), they are considered to continuously exchange photons, and it is this exchange that transmits the force between them. The photon is thus called the 'force carrier' (or gauge boson) of the electromagnetic interaction, just as gluons carry the strong force and W/Z bosons carry the weak force.
Briefly explain the phenomenon of photoelectric effect with Einstein's equation.
The photoelectric effect is the emission of electrons from a metal surface when light of sufficiently high frequency (above the metal's threshold frequency) falls on it. Einstein explained this by treating light as a stream of photons, each of energy hf; a photon transfers its entire energy to a single electron, part of which (equal to the work function φ) is used to free the electron from the metal, and the rest becomes its kinetic energy:
KE_max = hf − φ (Einstein's photoelectric equation) …
The full model answer is in the app.
| Session | Questions |
|---|---|
| 2026 Annual | 11 |
| 2025 1st Annual | 12 |
| 2025 2nd Annual | 10 |
| 2024 Annual | 8 |
| 2023 Annual | 6 |
47 real Federal Board (FBISE) Physics questions on Dawn of Modern Physics from 2023 to 2026, for 11th and 12th class. Each one shows the session it came from.
No. We could not find an official FBISE marking scheme for these papers, so the answers and explanations are written by Tayyari Karo for practice. Check anything important with your teacher or textbook.
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