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Units and Dimensions NEET Questions: Answer Key, FAQs

Units and Dimensions in NEET focus on expertise the fundamental concepts of bodily quantities, their gadgets, and their dimensions. Students need to comprehend a way to convert between different units and derive the scale of various physical portions. Key topics consist of dimensional analysis, using the dimensional system, and the application of units in fixing issues. Mastery of this concept facilitates in expertise diverse physics ideas and aids in solving complex NEET questions efficiently.

  1. Introduction to Units and Dimensions
  2. Download: Units and Dimensions​
  3. Basic Definitions: Units and Dimensions
  4. Dimensional Analysis: Units and Dimensions
  5. Dimensional Consistency: Units and Dimensions​
  6. Units of Measurement: Units and Dimensions​
  7. Dimensional Equations and Their Use: Units and Dimensions​
  8. Important Dimensional Formulas: Units and Dimensions​
  9. Applications of Units and Dimensions​
  10. FAQs about Units and Dimensions​

Introduction to Units and Dimensions

Units and Dimensions is a essential idea in physics, specifically relevant for the NEET examination, as it paperwork the foundation of knowledge bodily quantities. This subject matter specializes in the dimension of physical portions, their gadgets, and the relationships between them. It enables college students recognize how exclusive gadgets, like meters, kilograms, and seconds, are used to quantify diverse physical phenomena. Additionally, it introduces the concept of dimensional analysis, that’s vital for fixing complicated physics troubles and verifying the correctness of equations. Questions based totally on units and dimensions in NEET often test the student’s potential to apply dimensional formulas, convert gadgets, and analyze physical equations. Mastering this topic now not handiest strengthens hassle-fixing skills however additionally enhances the general knowledge of physics ideas.

Units And Dimensions Neet Questions

Key Concepts in Units and Dimensions

Physical Quantities:

  • Fundamental Quantities: These are unbiased portions that can’t be derived from others. Examples include length, mass, time, temperature, electric current, amount of substance, and luminous intensity.
  • Derived Quantities: These are quantities derived from fundamental quantities. Examples include velocity, acceleration, force, work, energy, etc.

Units:

  • System of Units: A system of units is a collection of units used to measure physical quantities.
  • SI Units: The International System of Units (SI) is the most widely used system of units. It includes seven base units: meter (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for electric current, kelvin (K) for temperature, mole (mol) for amount of substance, and candela (cd) for luminous intensity.

Dimensions:

  • Dimensional Formula: Represents the powers to which the fundamental units must be raised to obtain the unit of a derived quantity. For example, the dimensional formula for speed is [LT-1].
  • Dimensional Analysis: Involves studying the dimensions of physical quantities to check the correctness of equations and derive relationships between them.
  • Principle of Homogeneity of Dimensions: This principle states that the dimensions of each term in an equation must be the same.

Important Points to Remember:

  • Dimensionless quantities have no units.
  • The numerical value of a physical quantity depends on the system of units used.
  • Dimensional analysis can be used to check the correctness of equations but cannot determine the exact numerical value of a quantity.
  • It is important to use consistent units throughout calculations to avoid errors.

Download: Units and Dimensions

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Units and Dimensions NEET Questions with AnswerClick 

Basic Definitions: Units and Dimensions

Term Definition Example
Fundamental Quantities Independent quantities that cannot be derived from others Length, mass, time, temperature, electric current, amount of substance, luminous intensity
Derived Quantities Quantities derived from fundamental quantities Velocity (length/time), acceleration (length/time^2), force (mass*length/time^2), work (force*length), power (work/time)
SI Units The International System of Units, the most widely used system of units Meter (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), candela (cd)
CGS System Centimeter-Gram-Second system, another system of units Centimeter (cm), gram (g), second (s)
FPS System Foot-Pound-Second system, another system of units Foot (ft), pound (lb), second (s)

Dimensional Analysis: Units and Dimensions

Dimensional Evaluation

Dimensional evaluation is an effective technique used to investigate the relationships between exclusive physical quantities by determining their base quantities and units of measurement. It involves tracking these dimensions as calculations or comparisons are performed.

Concept of Dimensional Analysis

Base Quantities and Units:
  • There are seven essential base quantities: length (L), mass (M), time (T), electric current (I), temperature (θ), amount of substance (n), and luminous intensity (cd).
  • Each base quantity has a corresponding base unit: meter (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd).
Derived Quantities and Units:
  • Derived quantities are combinations of base quantities.
  • Examples:
    • Velocity: Length/Time (L/T)
    • Acceleration: Length/Time2 (L/T2)
    • Force: Mass x Acceleration (ML/T2)
    • Energy: Force x Distance (ML2/T2)
Principle of Homogeneity:

In any equation, the dimensions of all terms on both sides must be the same. This principle is essential to dimensional analysis.+

Dimensional Formulae for Common Physical Quantities

Physical Quantity Dimensional Formula
Length [L]
Mass [M]
Time [T]
Velocity [LT-1]
Acceleration [LT-2]
Force [MLT-2]
Work, Energy [ML2T-2]
Power [ML2T-3]
Momentum [MLT-1]
Pressure [ML-1T-2]
Density [ML-3]

Applications of Dimensional Analysis

Checking the Correctness of Equations:

By making sure that the dimensions on each side of an equation are equal, we can confirm its correctness.

Deriving New Equations:

Dimensional analysis can help us determine the form of an equation with respect to certain variables.

Converting Units:

Using conversion factors, we can convert units from one system to another.

Solving Problems:

Dimensional analysis can be used to solve problems involving physical quantities, especially when the exact relationship between variables is unknown.

Example:

Let’s derive the formula for the period (T) of a simple pendulum. We know that T depends on the length (L) of the pendulum and acceleration due to gravity (g).

T = kL^a g^b

Where k is a dimensionless constant.

Using dimensional analysis:

[T] = [L]^a [LT^-2]^b

Comparing powers of L and T on each side:

a + b = 0
-2b = 1

Solving these equations, we get:

a = 1/2
b = -1/2

Therefore, the formula for the period of a simple pendulum is:

T = k√(L/g)

This is the correct formula, and dimensional analysis has helped us derive it without knowing the exact mathematical derivation.

Limitations of Dimensional Analysis

  • It cannot determine the value of dimensionless constants.
  • It cannot distinguish between different physical quantities with the same dimensions.
  • It cannot provide information about the mathematical form of the equation.

Dimensional Consistency: Units and Dimensions

Method Description Example
Direct Comparison Compare the scale of every time period inside the equation. All phrases should have the equal dimensions. Equation: v = u + at Dimensions: [LT^-1] = [LT^-1] + [LT^-2][T]
Factor-Label Method Convert gadgets the usage of conversion elements to make certain dimensional consistency. Convert 10 m/s to km/hr: 10 m/s * (1 km / 1000 m) * (3600 s / 1 hr) = 36 km/hr
Dimensional Analysis Use the precept that best portions with the same dimensions may be introduced, subtracted, or equated. Derive the formulation during a pendulum: T ∝ √(l/g)

Units of Measurement: Units and Dimensions

International System of Units (SI)

The International System of Units (SI) is the contemporary form of the metric machine, and is the maximum widely used machine of size. It comprises a coherent gadget of gadgets of dimension constructed around seven base units.

Base Quantity Base Unit Symbol
Length meter m
Mass kilogram kg
Time second s
Electric Current ampere A
Thermodynamic Temperature kelvin K
Amount of Substance mole mol
Luminous Intensity candela cd

CGS and MKS Systems

CGS System: Centimeter-Gram-Second device. It is a variation of the metric gadget where the base gadgets are centimeter (cm), gram (g), and 2nd (s).

MKS System: Meter-Kilogram-Second system. It is a precursor to the SI gadget, the usage of meter (m), kilogram (kg), and 2nd (s) as base gadgets.

Conversion of Units

To convert units from one gadget to another, we use conversion elements. A conversion element is a ratio of equal portions expressed in one-of-a-kind units.

Example:

To convert 10 meters to centimeters:

  • 1 meter = one hundred centimeters
  • So, 10 meters = 10 * 100 centimeters = a thousand centimeters

Common Conversion Factors:

Length:
  • 1 inch = 2.54 centimeters
  • 1 foot = 12 inches
  • 1 backyard = 3 toes
  • 1 mile = 5280 feet
Mass:
  • 1 kilogram = 1000 grams
  • 1 pound = 0.453592 kilograms
  • 1 ton = 2000 pounds
Time:
  • 1 minute = 60 seconds
  • 1 hour = 60 mins
  • 1 day = 24 hours

Dimensional Equations and Their Use: Units and Dimensions

Topic Explanation Example
Derivation of Dimensional Equations 1. Identify the fundamental quantities: Determine the basic units (mass, length, time) involved in the physical quantity. 2. Express the quantity in terms of fundamental units: Write the formula for the quantity and substitute the fundamental units for each derived unit. 3. Write the dimensional formula: Represent the dimensions of mass, length, and time using symbols like [M], [L], and [T], respectively. For example, to find the dimensional formula of velocity: Velocity = Distance/Time = [L]/[T] = [LT^-1]
Use of Dimensional Analysis in Deriving Formulas Dimensional analysis can help derive relationships between physical quantities by ensuring dimensional homogeneity. This involves: 1. Identifying the relevant variables: Determine the physical quantities that influence the phenomenon. 2. Expressing the variables in terms of fundamental units: Write the dimensional formulas for each variable. 3. Forming a dimensionless equation: Combine the variables in a way that cancels out all dimensions. 4. Derive the formula: Based on the dimensionless equation, derive the formula relating the variables. Example: Deriving the formula for the period of a simple pendulum: Relevant variables: Length (L), Acceleration due to gravity (g) Dimensional formula of L: [L] Dimensional formula of g: [LT^-2] To form a dimensionless equation, we need to combine L and g in a way that cancels out all dimensions. One possible combination is: T ∝ √(L/g) This leads to the formula: T = 2π√(L/g)
Examples of Dimensional Derivations 1. Force: F = ma = [M][LT^-2] = [MLT^-2] 2. Energy: E = Fd = [MLT^-2][L] = [ML^2T^-2] 3. Power: P = W/t = [ML^2T^-2]/[T] = [ML^2T^-3]

Important Dimensional Formulas: Units and Dimensions

Here are the dimensional formulation for some essential bodily portions:

1. Base Quantities

  • Mass (M): [M]
  • Length (L): [L]
  • Time (T): [T]
  • Temperature (θ): [θ]
  • Electric Current (I): [I]
  • Amount of Substance (mol): [mol]
  • Luminous Intensity (cd): [cd]

2. Derived Quantities

  • Acceleration: [LT⁻²]
  • Force: [MLT⁻²]
  • Energy: [ML²T⁻²]
  • Power: [ML²T⁻³]
  • Gravitational Potential Energy: [ML²T⁻²]

Gravitational Potential Energy and Related Concepts

  • Gravitational Potential Energy (U): [ML²T⁻²]
  • Gravitational Potential (V): [L²T⁻²]
  • Gravitational Field Strength (g): [LT⁻²]
  • Gravitational Constant (G): [M⁻¹L³T⁻²]

Understanding Dimensional Formulas

Dimensional Formula: A representation of a bodily amount in phrases of its base dimensions.

Importance:

  • Checking the correctness of equations: Ensure that both aspects of an equation have the equal dimensions.
  • Deriving gadgets: Determine the units of a bodily quantity based on its dimensional formulation.
  • Converting devices: Convert devices from one gadget to another the use of dimensional analysis.
  • Understanding bodily relationships: Gain insights into how physical portions are associated with each other.

Example:

To take a look at the correctness of the equation for kinetic electricity, KE = 1/2mv², we can analyze the dimensions of each sides:

  • Left-hand side (KE): [ML²T⁻²]
  • Right-hand aspect (1/2mv²): [M][LT⁻¹]² = [ML²T⁻²]

Applications of Units and Dimensions

Application Description Example
Unit Conversion Problems Converting a physical quantity from one system of units to another. Converting 10 miles/hour to meters/second.
Error Analysis Using Dimensional Analysis Identifying and correcting errors in equations or calculations by checking the dimensional consistency of terms. Verifying the correctness of the equation for kinetic energy: KE = 1/2 mv^2.
Estimation of Physical Constants Determining the approximate value of a physical constant using dimensional analysis and known relationships between other physical quantities. Estimating the value of the gravitational constant G using the period and radius of a planet’s orbit.

FAQs about Units and Dimensions

Q. What are Units and Dimensions?

Answer: Units are standards for measuring physical quantities, while dimensions describe the physical nature of a quantity (e.g., length [L], time [T], mass [M]).

Q. Why are Units and Dimensions important in NEET?

Answer: Understanding Units and Dimensions helps in solving problems related to physical quantities, ensuring accuracy in calculations and conversions during NEET.

Q. What is the Dimensional Formula?

Answer: The Dimensional Formula expresses a physical quantity in terms of fundamental quantities like mass (M), length (L), and time (T).

Q. How are Dimensional Formulas used in NEET?

Answer: Dimensional Formulas help in checking the correctness of equations, deriving relations, and solving problems involving physical quantities.

Q. What are the fundamental units in physics?

Answer: The fundamental units are meter (m) for length, kilogram (kg) for mass, and second (s) for time.

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