Important Questions Class 11 Physics Chapter 2

Important Questions for CBSE Class 11 Physics Chapter 2 – Units and Measurement

Students will learn in Class 11 Physics Chapter 2 that a unit is any physical quantity that is measured by comparing it to a basic, arbitrarily chosen, and internationally accepted reference standard. The outcome of a physical quantity measurement is expressed as a number (or numerical measure) followed by a unit.

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In this chapter, students will learn about fundamental or base units for base quantities. All other physical quantities have units that are combinations of the base units. The units obtained for the derived quantities are referred to as derived units. A complete set of these units, including both base and derived units, is known as the system of units.

At Extramarks, subject matter experts meticulously design the Class 11 Physics Chapter 2 Important Questions to help students practise and prepare for this chapter. The topics covered in Class 11 lay the foundation for Class 12, as well as for several competitive examinations.

As a result, for better preparation, students should consult additional resources such as Class 11 Physics Chapter 2 Important Questions.

CBSE Class 11 Physics Chapter-2 Important Questions

Important Questions for Class 11 Physics Chapter 2 – Units and Measurements

This article contains some of the Important Questions for Physics Class 11 Chapter 2. Click the link to get full access to more such questions for Class 11 Physics Chapter 2 Important Questions on the Extramarks website.

1 Marks Answers and Questions

Q.1 Name physical quantities whose units are Electron Volt and Pascal.

Ans: The physical quantities whose units are Electron Volt and Pascal, are energy and pressure respectively.

Q.2 Define the SI Solid Angle Unit.

Ans: The SI unit for a solid angle is the steradian. A steradian is defined as the angle formed by a unit square metre area spherical plane at the centre of a unit length radius sphere.

2 Marks Answers and Questions

Q.1 Explain the following statement.

“To call a dimensional quantity ‘large’ or ‘small’ is meaningless without specifying a standard for comparison”.

Ans: The given statement is true because a dimensionless quantity can be large or small, but it must be compared to some standard. The coefficient of friction, for example, is dimensionless, but we can say that the coefficient of sliding friction is greater than the coefficient of rolling friction but less than the coefficient of static friction.

Q.2: 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 (hilltops, 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.)

Ans: The phenomenon observed in the above case refers to the line-of-sight. It is defined as an imaginary line joining an object and an observer’s eye. When we observe nearby stationary objects such as trees, houses, etc., while sitting in a moving train, they appear to move rapidly in the opposite direction because the line-of-sight changes very rapidly.

On the other hand, distant objects such as trees, stars, etc., appear stationary because of the large distance. As a result, the line-of-sight does not change its direction rapidly.

Q.3 Precise measurements of physical quantities are a need of science. Comment.

(For example, to ascertain the speed of an aircraft, one must have an accurate method to find its positions at closely separated instants of time. This was the driving force behind the development of radar during World War II.

Ans: It is indeed very true that precise measurements of physical quantities are essential for the development of science. Some examples are:

Ultrashort laser pulses (time interval ∼10−15s) are used to measure time intervals in several physical and chemical processes.

X-ray spectroscopy is used to determine the interatomic separation or inter-planar spacing.

The development of the mass spectrometer makes it possible to measure the mass of atoms precisely.

Q.4 Think of different examples in modern science where precise measurements of length, time, mass, etc., are needed. Also, give a quantitative idea of the precision needed, wherever possible.

Ans: It is indeed very true that precise measurements of physical quantities are essential for the development of science. Some examples are as follows.

1. Ultrashort laser pulses (time interval ∼10−15s) are used to measure time intervals in several physical and chemical processes.
2. X-ray spectroscopy is used to determine interatomic separation or inter-planar spacing.
3. The development of the mass spectrometer makes it possible to measure the mass of atoms precisely.

3  Marks Questions and Answers

Q.1 A new length unit is chosen so that the speed of light in vacuum is unity.What is the new unit distance between the Sun and the Earth if light takes 8 minutes and 20 seconds to cover this distance?

Ans:

The distance between the sun and the earth is given by:

x = speed of light/time required for light to travel the distance

We are given, in the new unit, the speed of light, c=1 unit

Time taken, t=8 min 20 s=500 s

∴ Distance between the Sun and the Earth x′=c×t′=1×500=500 units

Q.2 A student measures the thickness of a human hair using a microscope with a magnification of 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. Determine the thickness of your hair.

Ans:

We are given:

Magnification of the microscope =100

Average width of the hair in the field of view of the microscope =3.5 mm

∴ Actual thickness of the hair would be, 3.5100= 0.035mm

4 Marks Question and Answer

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

Ans:

Radius of hydrogen atom, r=0.5A∘=0.5×10−10m

Volume of hydrogen atom, V= 43 r2

⇒  V= 43 227 (0.5×10−10)3=0.524×10−30m3

Now, 1 mole of hydrogen contains 6.023×1023 hydrogen atoms.

∴ Volume of 1 mole of hydrogen atoms, Va=6.023×1023×0.524×10−30=3.16×10−7m3

Molar volume of 1 mole of hydrogen atoms at STP,

Vm=22.4L=22.4×10−3m3

So, the required ratio would be,

VmVa= 22.4 10-33.16 10-7= 7.08 104

Hence, we found that the molar volume is 7.08×104 times higher than the atomic volume. For this reason, the interatomic separation in hydrogen gas is much larger than the size of a hydrogen atom.

5 Marks Answers and Questions

Q.1: Just as precise measurements are necessary in Science; it is equally important to be able to make rough estimates of quantities using rudimentary ideas and common observations. Think of ways by which you can estimate the following (where an estimate is difficult to obtain, try to get an upper bound on the quantity):

• The Total Mass of Rain-Bearing Clouds Over India During the Monsoon.

Ans:

For estimating the total mass of rain-bearing clouds over India during the Monsoon:

During monsoons, a meteorologist records about 215 cm of rainfall in India, i.e., the height of the water column, h=215 cm=2.15 m

We have the following information,

Area of country, A=3.3×1012m2

Hence, the volume of rainwater, V=A×h=7.09×1012m3

Density of water, ρ=1×103kg m−3

We can find the mass from the given value of density and volume as,

M=ρ×V=7.09×1015kg

Hence, the total mass of rain-bearing clouds over India is approximately found to be  7.09×1015kg

1. The Mass of an Elephant.

Ans:

For estimating the mass of an elephant:

Consider a ship floating in the sea whose base area is known. Measure its depth at sea (say d1).

Volume of water displaced by the ship would be, Vb=Ad1

Now one could move an elephant on the ship and then measure the depth of the ship (d2).

Let the volume of water displaced by the ship with the elephant on board be given as Vbe=Ad2.

Then the volume of water displaced by the elephant =Ad2−Ad1 .

If the density of water =D

Mass of an elephant would be M=AD(d2−d1).

2. The Wind Speed During a Storm.

Ans: Estimation of wind speed during a storm:

Wind speed during a storm can be measured by using an anemometer. As wind blows, it rotates and the number of rotations in one second as recorded by the anemometer gives the value of wind speed.

3. The Number of Strands of Hair on Your Head.

Ans: Estimation of the number of strands of hair on your head:

Let the area of the head surface carrying hair be A

The radius of a hair can be determined with the help of a screw gauge and let it be r

∴ Area of one hair strand =πr2

Number of strands of hair ≈ Total surface areaArea of one hair = ar2

4. The Number of Air Molecules in Your Classroom.

Ans:

Estimation of the number of air molecules in your classroom:

Let the volume of the room be V

We know that:

One mole of air at NTP occupies 22.4 l

i.e., 22.4×10−3m3 volume.

Number of molecules in one mole NA=6.023×1023 (Avogadro number)

∴ Number of molecules in room of volume(V) could be found as,

n= 6.023 102322.410-3

⇒n=134.915×1026V

∴n=1.35×1028V

Chapter 2 Physics Class 11 Important Questions – Download

Chapter 2 Class 11 Physics Important Questions is easily accessible on the Extramarks website. The set of questions is useful for students’ revision and practise. This set helps the students understand the types of questions asked in the examinations, and how to answer them, and allows them to practise questions for all of the curriculum’s topics and sub-topics.

Students must use an additional practise resource like Important Questions Class 11 Physics Chapter 2  to gain a thorough understanding of all concepts and  learn different approaches to answering questions.

Important Questions for Class 11 Physics Chapter 2 – Related Essential Concepts

There are several topics associated with the syllabus from which questions in the examinations are asked. Here are some Important Questions for Class 11 Physics Chapter 2.

Unit and S.I. Unit

The measuring term for various types of quantities is unit. The following are the most common unit systems for measuring any quantity:

The S.I. System

The FPS System

The CGS System

The MKS System

To avoid confusion, the SI unit is the international measuring system that is used universally in scientific and technical research. This is the standard measuring system, which is useful because it allows people all over the world to understand measurements in a single-unit system. Different quantity measurements in physics require different SI units.

• In the CGS system, they were centimetre, gram, and second, respectively.
• In the FPS system, they were foot, pound, and second, respectively.
• In the MKS system, they were metre, kilogram, and second, respectively.

S.I. Base Unit: The base unit is the fundamental unit and the building block of any system. They are used for deriving the other units, e.g., Kilogram.

S.I. Derived Unit: The units derived from the base units are known as S.I. derived units.

Distance and its Units

Distance is the measurement of a body’s path between its initial and final positions. It is the product of speed and time, and it is represented as:

D = S × T.

Here,

D is the distance travelled by the body in metres.

T is the amount of time it took the body to travel the specified distance in seconds.

S denotes the body’s speed over the specified distance in metres per second.

For measuring distance, the most commonly used units are kilometre, metre, centimetre, and millimetre.

Mass and Weight

The amount of matter in an object is referred to as its mass. It is an intrinsic quantity of anyone and determines mass-dependent parameters. It helps in understanding the strength of an object’s gravitational attraction to other bodies, the item’s resistance to acceleration due to any force, inertia, and many other factors. It also aids in the formulation of the Theory of Relativity using E = mc2.

The weight of the body differs from its mass. Weight is the force exerted on the mass of anyone as a result of gravitational pull. The universal unit of measurement is mass, but the body’s weight varies due to the planet’s gravity. It is written as W = mg.

Atomic Mass Unit

Atomic Mass unit is useful when dealing with smaller atoms and molecules that have small masses making measuring them in kilograms inconvenient. One atomic mass unit equals one-twelfth of the mass of a C-12 carbon atom. It equals 1.22 x 10-27.

Other Important Concepts Related to CBSE Class 11 Physics Chapter 2 Important Questions

Aside from these concepts, Chapter 2 Units and Measurements of Class 11 Physics covers a wide range of other important topics. The chapter also includes time measurement and examines measurement errors such as absolute error, relative error, random error, systematic error, and gross error.  All of the concepts have some questions with varying marks in the exams and are required for both the school curriculum and competitive exam practice.

Important Questions for Class 11 Physics Chapter 2

1. Differentiate between A0 and A.U.
2. What is the S.I. unit of a solid angle?
3. Mention the physical quantities having the S.I. unit as Pascal and Electron Volt.
4. Suppose there is a planet X which is at a distance of 824.7 kilometres from Earth. The angular diameter of planet X is 35.7211 arcs. Calculate the diameter of planet X.
5. There is a radar signal that beams towards  planet X from the Earth, and then the echo for the same is received after seven minutes. Calculate the signal’s velocity, if we have the distance between the Earth and planet X to be 6.3 x 1010 m.
6. Calculate the dimensions of the specific heat and the latent heat.
7. G, E, m, and l denote Gravitational constant, energy, mass, and angular momentum, respectively. Determine the dimension for the given term: El2 / m3G2.
8. Calculate the maximum time that a light beam will take to pass through a nucleus of diameter 1.56 x 10-16 m. (The speed of light is 3 x 108 m/s).
9. If we chose  time, force, and velocity as the basic quantities, calculate the dimension of mass accordingly.
10. A calorie refers to the standard unit of energy or heat and is equal to 4.2 Joules. Here, 1J = 1 Kg m2 / s2. Suppose we get a unit system where the mass unit is equal to a kg, and length equals to bm, the time is ys. Now show that the magnitude of a calorie is 4.2 a-1 b-2 y2, according to the new units taken.

Benefits of Important Questions for Class 11 Physics Chapter 2

The set of Chapter 2 Class 11 Physics Important Questions is critical for students’ preparation and practise, and it will help them pass their exams with flying colours. Here are some of the key advantages of keeping a list of important questions on hand.

• Important Questions Class 11 Physics Chapter 2 is important because it provides students with practise material for all types of questions, allowing them to be confident when answering examination questions.
• Chapter 2 Class 11 Physics Important Questions gives students a quick overview of the various concepts asked in the questions, as well as multiple approaches to solving them.
• The question set is explicitly designed by subject matter experts, who compile the solutions in an easy-to-understand format.

Conclusion

Important Questions Class 11 Physics Chapter 2 is easily accessible from the Extramarks website, ensuring that students can prepare and practise well for the exams. Class 11 Physics Chapter 2 Important Questions include questions about various important concepts in Chapter Units and Measurements and help students become acquainted with the various types of questions and multiple solutions to them.As a result, to achieve the best results in the exams, students must prepare using these additional sets of questions.

Q.1Read the assertion and reason carefully to mark the correct option out of the options given below.

Assertion: The atomic clock cannot give most accurate and precise time in all conditions.

Reason: The reading of the atomic clock can differ as it is based on the frequency and temperature of the sample atom.

Marks:1

Ans

An atomic clock is a device that measures time by tuning the frequency of microwave wave with the atomic oscillation when they change energy levels. The atomic clocks are so precise and consistent that they would have to run for thousand years before their readings would differ by more than 1 second.

Q.2The dimensional formula for the coefficient of viscosity is

Marks:1

Ans

[ML -1T1]

Coefficient of viscosity, ? =  F × r A × v ?[ ? ] = [ ML -1 T -1 ]

Q.3The density of a cube is measured by measuring its mass and the length of its sides. If the maximum errors in the measurement of mass and length are 3% and 2% respectively, then the maximum error in the measurement of the density of cube is

5%

7%

9%

10%

Marks:1

Ans

Density,d =M L 3 Maximum error in measurement of mass, (M M ×100 ) max  =  3% Maximum error in measurement of length, (LL ×100 ) max  =  2% Maximum error in measurement of density, (d d×100 ) max = 3%+3×2%=9%

Q.4What is principle of homogeneity in dimensional method?

It states that the dimensions of each term on both sides of the equation should remain same.

Marks:1

Ans

It states that the dimensions of each term on both sides of the equation should remain same.

Q.5 What do you mean by significant figures? Discuss their rule also.

Marks:5

Ans

The significant figures are those figures, which are considered in the measurement. The following are the rule to measure the significant figures:

1: All non zero digits are significant e.g. the digit 3476, there are 4 significant figures.

2: All the zeros between non zero digits are significant e.g. 14005, there are 5 significant figures.

3: All zeros on the right of the last non-zero digit in the decimal part are significant e.g. 0.00800 has 3 significant figures.

4: All zeros on the right of non-zero digit are NOT significant e.g. 378000 has 3 significant figures.

5: In a number less than one, all zeros to the right of decimal point and to the left of non-zero digit are not significant. E.g. 0.0084 has 2 significant.