NCERT solutions for Physics [English] Class 11 chapter 1 - Units and Measurements [Latest edition]

The volume of a cube of side 1 cm is equal to ______ m³

The surface area of a solid cylinder of radius 2.0 cm and height 10.0 cm is equal to ______ (mm)².

A vehicle moving with a speed of 18 km h^–1covers ______ m in 1 s.

The relative density of lead is 11.3. Its density is ______ g cm^–3or ______ kg m^–3.

Fill in the blank by suitable conversion of unit: 

1 kg m²s^–2= ______ g cm² s^–2

Fill in the blank by suitable conversion of unit: 

1 m =______ ly

Fill in the blank by suitable conversion of unit:

3.0 m s^–2= ______ km h^–2

Fill in the blank by suitable conversion of unit: 

G = 6.67 × 10⁻¹¹ N m² (kg)⁻²= ______ (cm)³s⁻² g⁻¹

A calorie is a unit of heat or energy and it equals about 4.2 J where 1J = 1 kg m²s^–2. Suppose we employ a system of units in which the unit of mass equals α kg, the unit of length equals β m, the unit of time is γ s. Show that a calorie has a magnitude 4.2 α^–1 β^–2 γ² in terms of the new units.

Explain this statement clearly:

“To call a dimensional quantity ‘large’ or ‘small’ is meaningless without specifying a standard for comparison”. In view of this, reframe the following statements wherever necessary:

1. Atoms are very small objects
2. A jet plane moves with great speed
3. The mass of Jupiter is very large
4. The air inside this room contains a large number of molecules
5. A proton is much more massive than an electron
6. The speed of sound is much smaller than the speed of light.

A new unit of length is chosen such that the speed of light in vacuum is unity. What is the distance between the Sun and the Earth in terms of the new unit if light takes 8 min and 20 s to cover this distance?

Which of the following is the most precise device for measuring length:

1. a vernier callipers with 20 divisions on the sliding scale
2. a screw gauge of pitch 1 mm and 100 divisions on the circular scale
3. an optical instrument that can measure length to within a wavelength of light?

A student measures the thickness of a human hair by looking at it through a microscope of magnification 100. He makes 20 observations and finds that the average width of the hair in the field of view of the microscope is 3.5 mm. What is the estimate on the thickness of hair?

You are given a thread and a metre scale. How will you estimate the diameter of the thread?

A screw gauge has a pitch of 1.0 mm and 200 divisions on the circular scale. Do you think it is possible to increase the accuracy of the screw gauge arbitrarily by increasing the number of divisions on the circular scale?

The mean diameter of a thin brass rod is to be measured by vernier callipers. Why is a set of 100 measurements of the diameter expected to yield a more reliable estimate than a set of 5 measurements only?

The photograph of a house occupies an area of 1.75 cm²on a 35 mm slide. The slide is projected on to a screen, and the area of the house on the screen is 1.55 m². What is the linear magnification of the projector-screen arrangement?

State the number of significant figures in the following:

0.007 m²

State the number of significant figures in the following:

2.64 × 10²⁴ kg

State the number of significant figures in the following:

0.2370 g cm^–3

State the number of significant figures in the following:

6.320 J

State the number of significant figures in the following: 

6.032 N m^–2

State the number of significant figures in the following:

0.0006032 m²

The length, breadth, and thickness of a rectangular sheet of metal are 4.234 m, 1.005 m, and 2.01 cm respectively. Give the area and volume of the sheet to correct significant figures.

The mass of a box measured by a grocer’s balance is 2.300 kg. Two gold pieces of masses 20.15 g and 20.17 g are added to the box. What is

1. What is the total mass of the box?
2. What is the difference in the masses of the pieces to correct significant figures?

A famous relation in physics relates ‘moving mass’ m to the ‘rest mass’ m₀ of a particle in terms of its speed v and the speed of light, c. (This relation first arose as a consequence of special relativity due to Albert Einstein). A boy recalls the relation almost correctly but forgets where to put the constant c. He writes:

`m = m_0/(1-v^2)^(1/2)`

Guess where to put the missing c.

The unit of length convenient on the atomic scale is known as an angstrom and is denoted by Å : 1Å = 10⁻¹⁰ m. The size of a hydrogen atom is about 0.5 Å. What is the total atomic volume in m³ of a mole of hydrogen atoms?

One mole of an ideal gas at standard temperature and pressure occupies 22.4 L (molar volume). What is the ratio of molar volume to the atomic volume of a mole of hydrogen? (Take the size of hydrogen molecule to be about 1Å). Why is this ratio so large?

Explain this common observation clearly : If you look out of the window of a fast moving train, the nearby trees, houses, etc. seem to move rapidly in a direction opposite to the train’s motion, but the distant objects (hill tops, the Moon, the stars etc.) seem to be stationary. (In fact, since you are aware that you are moving, these distant objects seem to move with you).

The Sun is a hot plasma (ionized matter) with its inner core at a temperature exceeding 10⁷ 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 × 10³⁰ kg, radius of the Sun = 7.0 × 10⁸ m.