IBDP Physics- E.5 Fusion and stars- IB Style Questions For HL Paper 1A -FA 2025

Question

A star has a parallax angle of \( 1 \times 10^{-2} \) arc-second with respect to orbit of Earth. What is its distance from the Sun?

(A) 0.01 pc
(B) 0.02 pc
(C) 50 pc
(D) 100 pc

▶️ Answer/Explanation

Detailed solution

Distance in parsecs = 1 / parallax angle (in arc-seconds)
\( d = \frac{1}{1 \times 10^{-2}} = 100 \) pc
✅ Answer: (D) 100 pc

Question

What is the variation of nuclear density \( \rho \) with nucleon number \( A \)?

▶️ Answer / Explanation

Detailed explanation

The nuclear radius varies with nucleon number \(A\) as:

\[ R = R_0 A^{1/3} \]

Hence the nuclear volume is proportional to:

\[ V \propto R^3 \propto A \]

Since nuclear mass is also proportional to \(A\), the nuclear density:

\[ \rho = \frac{\text{mass}}{\text{volume}} \]

is approximately constant for all nuclei.

✅ Answer: (B)