(solved)Question 2.23 of NCERT Class XI Physics Chapter 2

Question 2.23
NCERT Class XI Physics

The Sun is a hot plasma (ionized matter) with its inner core at a temperature exceeding 10^7 K, and its outer surface at a temperature of about 6000 K. At these high temperatures, no substance remains in a solid or liquid phase. In what range do you expect the mass density of the Sun to be, in the range of densities of solids and liquids or gases? Check if your guess is correct from the following data : mass of the Sun = 2.0 × 10^30 kg, radius of the Sun = 7.0 × 10^8 m.

Physical Concept

Sun is a plasma because its high temperature prevents existence in liquid or solid state, and the strong gravitation prevents it from existing in gaseous state.

The density can be expected to be in the range of solids and liquids.

Video Explanation

Please watch this youtube video for a quick explanation of the solution:

Solution

$ \begin{aligned} &\text{mass m} = 2.0 \times 10^{30} \text{ kg}\\ &\text{radius R} = 7.0 \times 10^8 \text{ m}\\\\ &\text{density } \rho = \frac{\text{mass}}{\text{volume}}\\\\ &\text{SF in m and R both are same } = 2\\ &\text{after division density will have } = 2\\\\ &\therefore \rho = \frac{2.0 \times 10^{30}}{4\pi/3 \times (7.0 \times 10^8)^3}\\\\ &= 1.392 \times 10^3 \text{ kg m}^{-3}\\\\ &\text{rounding to }2 \text{ places,}\\ &1.4 \times 10^3 \text{ kg m}^{-3}\:\underline{Ans}\\ &\text{(range is of solids and liquids)} \end{aligned} $