CBSE Class 12 Physics 2024: question 28

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. (a) Any two properties: (1) The nucleus is positively charged, with charge $+Ze$. (2) It consists of protons and neutrons (nucleons). Others: its radius is $R=R_0{A}^{1/3}$; nuclear density is independent of mass number.

   1 mark

2. (b) Almost the entire mass of an atom is concentrated in the nucleus, whose radius (~10⁻¹⁵ m) is about 10⁻⁵ times that of the atom (~10⁻¹⁰ m). Most of the atom's volume is empty space, so the nucleus has a far larger mass per unit volume.

   1 mark

3. (c) Let m be the mass of a nucleon. For mass number A, the mass is $mA$ and the radius is $R=R_0{A}^{1/3}$. Density $\rho =\frac{mA}{\frac{4}{3}\pi R^3}=\frac{mA}{\frac{4}{3}\pi R_0^{3}A}=\frac{3m}{4\pi R_0^3}$. This is independent of A, so nuclear density is the same for all nuclei (≈ $2.3\times 10^{17}$ kg m⁻³).

   1 mark

Answer: (a) Positively charged; made of protons and neutrons (R = R₀A^{1/3}). (b) Mass concentrated in tiny volume, atom mostly empty. (c) ρ = 3m/(4πR₀³), independent of A.

Revise the chapter

• Chapter: Nuclei (notes, formulas, where marks are lost and every past question)
• Topic: Composition, Size and Density of Nucleus