Units, Dimensions and Measurement

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Questions and Answers

What is a physical quantity?

A quantity that can be explained by laws but not measured.

A quantity that can be measured and explained in terms of laws. (correct)

A quantity that can only be measured but not explained by laws.

A quantity that cannot be measured or explained by laws.

What is a fundamental quantity?

A quantity that is derived from other quantities.

A quantity that is independent of other quantities. (correct)

A quantity that is not measurable.

A quantity that is dependent on other quantities.

What is a vector quantity?

A quantity that has both magnitude and direction. (correct)

A quantity that has magnitude only.

A quantity that has neither magnitude nor direction.

A quantity that has direction only.

What is a derived quantity?

A quantity that is derived from fundamental quantities. Signup and view all the answers

What is an example of a derived quantity?

Area Signup and view all the answers

When refractive index is defined as Velocity of light in air/Velocity of light in medium, what does it imply about the velocity of light?

Velocity of light in air can be greater or less than in medium Signup and view all the answers

Which of the following is a derived quantity if speed and time are chosen as fundamental quantities?

Length Signup and view all the answers

A scalar quantity can have a negative:

Sign Signup and view all the answers

Strain is a measure of:

Change in dimension per unit original dimension Signup and view all the answers

What is the minimum number of fundamental quantities required to express all other quantities in mechanics?

Three Signup and view all the answers

What is the fundamental unit of mass in the CGS system?

gram Signup and view all the answers

Which system of units uses foot, pound, and second as fundamental units?

FPS system Signup and view all the answers

What is the unit of force in the FPS system?

poundal Signup and view all the answers

What is the standard unit of length in the CGS system?

centimetre Signup and view all the answers

Which of the following is a fundamental quantity in the MKS system?

Mass Signup and view all the answers

What is the unit of length in the CGS system?

Centimeter Signup and view all the answers

What is the prefix for 10^-6 in the S.I. system?

Micro Signup and view all the answers

What is the fundamental unit of time in the MKS system?

Second Signup and view all the answers

Which of the following is a unit of mass in the MKS system?

Kilogram Signup and view all the answers

What is the unit of length in the FPS system?

Foot Signup and view all the answers

What was the initial definition of the unit of time, the second, based on?

Rotation of the earth around the sun and its axis Signup and view all the answers

What is the relationship between the least count of a screw gauge and the accuracy of measurement?

Smaller the least count, higher is the accuracy Signup and view all the answers

What is a characteristic of a physical quantity that remains constant?

The product of the numerical value and the unit Signup and view all the answers

What is the effect of changing the unit of measurement on the significant figures of a physical quantity?

The significant figures remain the same Signup and view all the answers

What is a characteristic of a repetitive phenomenon that can be used to measure time?

Any of the above repetitive phenomena Signup and view all the answers

What is the equivalent value of 1 fermi in terms of meters?

10^(-10) m Signup and view all the answers

What is the mass of an electron in terms of kilograms?

9.1 × 10^(-25) kg Signup and view all the answers

What is the equivalent value of 1 angstrom in terms of meters?

10^(-10) m Signup and view all the answers

What is the value of 1 Chandra Shekhar unit in terms of kilograms?

2.8 × 10^(11) kg Signup and view all the answers

What is the equivalent value of 1 year in terms of time?

The time taken by the Earth to complete 1 revolution around the Sun in its orbit Signup and view all the answers

Study Notes

Practical Units

Length units include fermi (1 fm = 10^-15 m) and X-ray unit (1 XU = 10^-10 m).
Common practical units can be fundamental (like light year) or derived (like horsepower).
Angstrom (1 Å = 10^-10 m), micron (1 µm = 10^-6 m), and astronomical unit (1 A.U. = 1.49 × 10^11 m) are essential.
Light year is measured as 1 ly = 9.46 × 10^15 m, and a parsec (1 pc) equals 3.26 light years.

Mass Units

Chandra Shekhar unit (1 CSU = 1.4 times the Sun's mass ≈ 2.8 × 10^11 kg).
Metric tonne equals 1000 kg, and quintal equals 100 kg.
Atomic mass unit (1 amu = 1.67 × 10^-27 kg), with the mass of a proton or neutron approx 1 amu.

Time Measurement

A year is defined by Earth's revolution around the Sun.
Atomic standards for mass and time are being pursued due to variability.
Significant figures are crucial for accuracy; more figures yield better precision without changing across units.
In unit operations, the significant figures retained should equal the smallest number involved.

Systems of Units

CGS (centimetre-gram-second) system uses cm, g, and s as fundamental units.
MKS (metre-kilogram-second) system defines units as m, kg, and s.
FPS (foot-pound-second) system employs foot, pound, and second for measurements.
Derived units manifest as combinations of fundamental units.

Standards of Length, Mass, and Time

The standard metre now correlates with the wavelength of light, termed atomic standard of length.
Fundamental units can express all other units in mechanics, while derived units depend on these fundamentals.

Types of Physical Quantities

Scalar quantities (e.g., length, time) involve only magnitude and follow ordinary addition/subtraction laws.
Vector quantities include both magnitude and direction (e.g., force, velocity) and require vector algebra for operations.
Fundamental quantities are basic and independent (e.g., mass, length, time), serving as the foundation for derived quantities, which arise from combinations of fundamentals.

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Description

Test your understanding of physical quantities, units, and measurements in physics. Learn about fundamental and derived quantities, vector quantities, and more.