NCERT Class 11 Physics Solutions: Chapter 2-Unit and Measurement Part 13 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question: 2.23

The sun is a hot plasma (ionized matter) with its inner core at a temperature exceeding 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 radius of the Sun

Answer: 2.23

Image Shows the Meaning of Density
  • Mass of the Sun,
  • Radius of the Sun,
  • Volume of the Sun,

  • Density of the Sun

  • The density of the Sun is in the density range of solids and liquids. This high density is attributed to the intense gravitational attraction of the inner layers on the outer layer of the Sun.

Question: 2.24

When the planet Jupiter is at a distance of 824.7 million kilometers from the Earth, its angular diameter is measured to be 35.72 ″ of arc. Calculate the diameter of Jupiter.

Answer: 2.24

Figure Shows the Angular Diameter
  • Distance of Jupiter from the Earth,
  • Angular diameter rad
  • Diameter of Jupiter = d
  • Using the relation,

Question: 2.25

A man walking briskly in rain with speed v must slant his umbrella forward making an angle with the vertical. A student derives the following relation between and V: tan and checks that the relation has a correct limit: as as expected. (We are assuming there is no strong wind and that the rain falls vertically for a stationary man) . Do you think this relation can be correct? If not, guess the correct relation.

Answer: 2.25

  • Incorrect; on dimensional ground
  • The relation is
  • Dimension of R. H. S
  • Dimension of L. H. S

( The trigonometric function is considered to be a dimensionless quantity)

  • Dimension of R. H. S is not equal to the dimension of L. H. S. Hence, the given relation is not correct dimensionally.
  • To make the given relation correct, the R. H. S should also be dimensionless. One way to achieve this is by dividing the R. H. S by the speed of rainfall
  • Therefore, the relation reduces to

  • This relation is dimensionally correct.

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