CBSE Class 12 Physics 2024: question 21

Hints

Open one hint at a time and try again before the next.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

1. Bohr's quantisation condition: $mvr=\frac{nh}{2\pi }$, so $n=\frac{2\pi mvr}{h}$.

   1 mark

2. Substituting: $n=\frac{2\times 3.14\times 6.0\times 10^{24}\times 3\times 10^4\times 1.5\times 10^{11}}{6.63\times 10^{-34}}$

   ½ mark

3. $n\approx 2.56\times 10^{74}$

   This is enormously large, so quantisation of the earth's orbit is not noticeable.

   ½ mark

Answer: n ≈ 2.56 × 10⁷⁴

Revise the chapter

• Chapter: Atoms (notes, formulas, where marks are lost and every past question)