RE-NEET 2026 Physics Photon and Electron Momentum MCQ Question

✅ Ans: 2 → 225

Key Concept:

For photon:

$$p_{ph}=\frac{E}{c}$$

For electron:

$$p_e=\sqrt{2m_eE}$$

Therefore,

$$\frac{p_e}{p_{ph}} =\frac{\sqrt{2m_eE}\,c}{E} =c\sqrt{\frac{2m_e}{E}}$$

For $E=20\,eV$:

$$\boxed{\frac{p_e}{p_{ph}}\approx225}$$

❌ Why other options are wrong?

• 1/250 ❌ → ratio is inverted
• 275 ❌ → incorrect numerical substitution
• 2/2450 ❌ → incorrect momentum relation

📌 NCERT: “The momentum of a photon is $p=h/\lambda=E/c$.”

🧠 NEET Trick: Same energy → photon momentum $=E/c$, electron momentum $=\sqrt{2mE}$.