Physics · Nuclear Physics

JEE Main 2024 — 9 April, Shift 1 — Question 52

A star has 100%100 \% helium composition. It starts to convert three 4He{ }^{4} \mathrm{He} into one 12C{ }^{12} \mathrm{C} via triple alpha process as

4He+4He+4He→12C+Q{ }^{4} \mathrm{He}+{ }^{4} \mathrm{He}+{ }^{4} \mathrm{He} \rightarrow{ }^{12} \mathrm{C}+\mathrm{Q}. The mass of the star is 2.0×1032 kg2.0 \times 10^{32} \mathrm{~kg} and it generates energy at the rate of

5.808×1030 W5.808 \times 10^{30} \mathrm{~W}. The rate of converting these 4He{ }^{4} \mathrm{He} to 12C{ }^{12} \mathrm{C} is n×1042 s−1\mathrm{n} \times 10^{42} \mathrm{~s}^{-1},

where n is \qquad . [Take, mass of 4He=4.0026u{ }^{4} \mathrm{He}=4.0026 \mathrm{u}, mass of 12C=12u{ }^{12} \mathrm{C}=12 \mathrm{u} ]

Answer: 15

Numerical answer — enter this value.

Step-by-step solution

4He+4He+4He→12C+Q\quad{ }^{4} \mathrm{He}+{ }^{4} \mathrm{He}+{ }^{4} \mathrm{He} \rightarrow{ }^{12} \mathrm{C}+\mathrm{Q}

power generated =NtQ=\frac{\mathrm{N}}{\mathrm{t}} \mathrm{Q}

where, N→\mathrm{N} \rightarrow No. of reaction /sec/ \mathrm{sec}.

Q=(3 mHe−mC)C2\mathrm{Q}=\left(3 \mathrm{~m}_{\mathrm{He}}-\mathrm{m}_{\mathrm{C}}\right) \mathrm{C}^{2} Q=(3×4.0026−12)(3×108)2\mathrm{Q}=(3 \times 4.0026-12)\left(3 \times 10^{8}\right)^{2}

Q=7.266MeV\mathrm{Q}=7.266 \mathrm{MeV}

Nt= power Q=5.808×10307.266×106×1.6×10−19\frac{\mathrm{N}}{\mathrm{t}}=\frac{\text { power }}{\mathrm{Q}}=\frac{5.808 \times 10^{30}}{7.266 \times 10^{6} \times 1.6 \times 10^{-19}}

Nt=5×1042\frac{\mathrm{N}}{\mathrm{t}}=5 \times 10^{42}

rate of conversion of 4He{ }^{4} \mathrm{He} into 12C=15×1042{ }^{12} \mathrm{C}=15 \times 10^{42}

Hence, n=15\mathrm{n}=15

Answer key and solution verified before publishing.

Practise Nuclear Physics

Start with this question, then two more from the same chapter — with a tutor that explains every step. Free.

Exam
JEE Main 2024
Subject
Physics
Chapter
Nuclear Physics
Topic
Nuclear Fission and Fusion