Unit 1, Topic 1.2 Physical Quantities Questions and Answers – Short & Long Questions

Chapter 1 Physical Quantities and Measurement Physics Notes | Complete Guide with Formulas & Derivations 

1.2 Physical Quantities Expected Board Short & Long Questions 

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Short Questions

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1. Define a physical quantity.

Answer:
A physical quantity is a measurable property of a physical object or phenomenon that can be expressed by a numerical value and a unit.

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2. What are the two components of a physical quantity?

Answer:
The two components of a physical quantity are:

1. Numerical value — tells the magnitude of the quantity.
2. Unit — provides the standard used for measurement.

For example, in 5 m, 5 is the numerical value and m is the unit.

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3. What is a fundamental quantity?

Answer:
A fundamental quantity is a physical quantity that is independent of other physical quantities and cannot be expressed in terms of other physical quantities.

Examples include length, mass, and time.

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4. What is a derived quantity?

Answer:
A derived quantity is a physical quantity that is obtained by combining fundamental quantities mathematically.

For example, speed is a derived quantity because:

$v=\frac{d}{t}$

where distance and time are fundamental quantities.

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5. Name the seven SI base quantities.

Answer:
The seven SI base quantities are:

1. Length
2. Mass
3. Time
4. Electric current
5. Thermodynamic temperature
6. Amount of substance
7. Luminous intensity

Their SI units are metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd), respectively.

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6. Give three examples of derived quantities.

Answer:
Three examples of derived quantities are:

1. Speed
2. Acceleration
3. Density

Other examples include area, volume, force, work, energy, power, and pressure.

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7. What is a scalar quantity?

Answer:
A scalar quantity is a physical quantity that has magnitude only and does not require a direction for its complete description.

Examples include mass, time, temperature, distance, and speed.

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8. What is a vector quantity?

Answer:
A vector quantity is a physical quantity that has both magnitude and direction.

Examples include displacement, velocity, acceleration, and force.

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9. Give two examples each of scalar and vector quantities.

Answer:

Scalar quantities:

• Mass
• Temperature

Vector quantities:

• Force
• Displacement

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10. Why is area considered a derived quantity?

Answer:
Area is considered a derived quantity because it is obtained by multiplying two lengths. Since length is a fundamental quantity, area is derived from it.

For a rectangular surface:

$A=l\times w$

Therefore, its SI unit is:

$\text{m}\times \text{m}={\text{m}}^2$

Hence, area is a derived quantity.

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Long Questions

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1. Define physical quantities and explain their classification.

Answer:
A physical quantity is a measurable property of a physical object or phenomenon that can be expressed by a numerical value and a unit.

Physical quantities can be classified in two important ways.

Classification according to their dependence

1. Fundamental quantities:
These are independent physical quantities that cannot be expressed in terms of other physical quantities. There are seven SI base quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity.

2. Derived quantities:
These are obtained by mathematically combining fundamental quantities. Examples include speed, acceleration, area, volume, force, energy, and density.

For example, speed is given by:

$v=\frac{d}{t}$

Since distance and time are fundamental quantities, speed is a derived quantity.

Classification according to direction

Physical quantities can also be classified as:

1. Scalar quantities: Have magnitude only, such as mass, time, temperature, and speed.

2. Vector quantities: Have both magnitude and direction, such as displacement, velocity, acceleration, and force.

Thus, physical quantities provide a quantitative description of physical objects and phenomena.

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2. Describe the seven fundamental physical quantities and their SI units.

Answer:
The SI system contains seven fundamental physical quantities. Each has a corresponding SI base unit.

Fundamental Quantity	SI Base Unit	Symbol
Length	metre	m
Mass	kilogram	kg
Time	second	s
Electric current	ampere	A
Thermodynamic temperature	kelvin	K
Amount of substance	mole	mol
Luminous intensity	candela	cd

1. Length
Length measures the extent or distance between two points. Its SI unit is the metre (m).

2. Mass
Mass is a measure of the amount of matter in an object. Its SI unit is the kilogram (kg).

3. Time
Time measures the duration between events. Its SI unit is the second (s).

4. Electric Current
Electric current represents the rate of flow of electric charge. Its SI unit is the ampere (A).

5. Thermodynamic Temperature
Temperature indicates the thermal state of a system. Its SI base unit is the kelvin (K).

6. Amount of Substance
Amount of substance measures the quantity of elementary entities such as atoms, molecules, or ions. Its SI unit is the mole (mol).

7. Luminous Intensity
Luminous intensity measures the strength of visible light emitted by a source in a particular direction. Its SI unit is the candela (cd).

These seven quantities form the foundation of the SI system, from which many derived quantities and units are constructed.

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3. Explain the difference between fundamental and derived quantities with examples.

Answer:

Fundamental Quantities

Fundamental quantities are independent quantities that cannot be expressed in terms of other physical quantities.

Examples include:

• Length
• Mass
• Time
• Electric current
• Thermodynamic temperature
• Amount of substance
• Luminous intensity

Their units are the seven SI base units.

Derived Quantities

Derived quantities are obtained by combining fundamental quantities mathematically.

Examples include:

• Area
• Volume
• Speed
• Acceleration
• Force
• Density
• Energy
• Power

For example, speed is given by:

$v=\frac{d}{t}$

Its SI unit is:

$\frac{\text{m}}{\text{s}}=\text{m/s}$

Similarly, density is given by:

$\rho =\frac{m}{V}$

and its SI unit is:

$\frac{\text{kg}}{{\text{m}}^3}$

Difference:

Fundamental Quantities	Derived Quantities
Independent quantities	Obtained from fundamental quantities
Cannot be expressed in terms of other physical quantities	Can be expressed using fundamental quantities
Have SI base units	Have derived SI units
Example: length	Example: speed
Example: mass	Example: density

Therefore, fundamental quantities form the basis from which derived quantities are obtained.

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4. Differentiate between scalar and vector quantities with suitable examples.

Answer:

Physical quantities can be classified as scalar or vector according to whether direction is required to describe them completely.

Scalar Quantities

A scalar quantity has magnitude only. Direction is not required.

Examples include:

• Mass
• Time
• Temperature
• Distance
• Speed
• Energy
• Volume

For example, 5 kg completely describes a mass because no direction is required.

Vector Quantities

A vector quantity has both magnitude and direction.

Examples include:

• Displacement
• Velocity
• Acceleration
• Force
• Momentum

For example, a velocity of 20 m/s eastward contains both magnitude and direction.

Comparison:

Scalar Quantity	Vector Quantity
Has magnitude only	Has magnitude and direction
Direction is not required	Direction is required
Can be described by a numerical value and unit	Requires magnitude, unit, and direction
Example: speed	Example: velocity
Example: distance	Example: displacement
Example: mass	Example: force

Therefore, the main difference is that a scalar has magnitude only, whereas a vector has both magnitude and direction.

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• ❓ Chapter 1 Questions & Answers
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  🧮 Chapter 1 Solved Numericals 

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