Verified Solution • 2025–26 Session moderate

QPage 363: Q1: Photoelectric Effect and Wave-Particle Duality Solutions — HC Verma: Concepts of Physics - Volume 2

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often insert $m=0$ into the non‑relativistic relation $p=mv$ and conclude a photon has zero momentum; remember $p=mv$ only holds for massive objects moving much slower than $c$. For photons use the relativistic expression $p=E/c= h/\lambda$, which does not involve a rest mass.

Can we find the mass of a photon by the definition p=mvp = mv?

Step-by-Step Verified Solution

**Answer:** No, we cannot find the mass of a photon by the definition p=mvp = mv. **Step-by-Step Explanation:** The equation p=mvp = mv is valid only for objects moving at speeds much slower than the speed of light. For a photon (a relativistic particle), the momentum is given by p=E/cp = E/c. A photon has zero rest mass. Therefore, putting m=0m = 0 in p=mvp = mv gives p=0p = 0, which is incorrect. The correct relation is p=E/cp = E/c.

All Questions in this Chapter

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