3marks Questions 1. Name The Fundamental Units And Supplementary Units On SI And Their Symbols Of Representation. 2 What Are The Advantages Of SI? Cm 3What Is Meant By Significant Figures? Give Any Four Rules For Counting Significant Figures. 5 Marks

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Understanding the Fundamentals of SI Units and Significant Figures

Introduction to SI Units

The International System of Units (SI) is a widely accepted system of measurement that provides a standardized way of expressing physical quantities. It consists of seven fundamental units and two supplementary units, which are used to express various physical quantities. In this article, we will discuss the fundamental and supplementary units of SI, their symbols, and the advantages of using the SI system.

Fundamental Units of SI

The seven fundamental units of SI are:

  • Meter (m): The unit of length, which is defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.
  • Kilogram (kg): The unit of mass, which is defined as the mass of the International Prototype of the Kilogram (IPK).
  • Second (s): The unit of time, which is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.
  • Ampere (A): The unit of electric current, which is defined as the flow of one coulomb per second.
  • Kelvin (K): The unit of thermodynamic temperature, which is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.
  • Mole (mol): The unit of amount of substance, which is defined as the amount of substance that contains as many particles (atoms, molecules, ions, etc.) as there are atoms in 0.012 kilograms of carbon-12.
  • Candela (cd): The unit of luminous intensity, which is defined as the luminous intensity of a source that emits monochromatic radiation of frequency 540 x 10^12 hertz and has a radiant intensity of 1/683 watts per steradian.

Supplementary Units of SI

The two supplementary units of SI are:

  • Radian (rad): The unit of plane angle, which is defined as the ratio of the arc length to the radius of a circle.
  • Steradian (sr): The unit of solid angle, which is defined as the ratio of the area of a sphere to the square of its radius.

Symbols of Representation

The symbols of representation for the fundamental and supplementary units of SI are:

  • m: Meter
  • kg: Kilogram
  • s: Second
  • A: Ampere
  • K: Kelvin
  • mol: Mole
  • cd: Candela
  • rad: Radian
  • sr: Steradian

Advantages of SI

The SI system has several advantages, including:

  • Universal acceptance: The SI system is widely accepted and used in most countries around the world.
  • Consistency: The SI system provides a consistent way of expressing physical quantities, which makes it easier to communicate and compare measurements.
  • Precision: The SI system provides a high degree of precision, which is essential for scientific and technological applications.
  • Flexibility: The SI system is flexible and can be used to express a wide range of physical quantities.

Significant Figures

Significant figures are the digits in a measurement that are known to be reliable and certain. They are used to express the precision of a measurement and to indicate the level of uncertainty associated with it. The number of significant figures in a measurement depends on the instrument used to make the measurement and the level of precision required.

Rules for Counting Significant Figures

There are four rules for counting significant figures:

  1. Non-zero digits are always significant: Any non-zero digit in a measurement is considered significant.
  2. Zeros between non-zero digits are significant: Zeros that are placed between non-zero digits are considered significant.
  3. Leading zeros are not significant: Zeros that are placed at the beginning of a measurement are not considered significant.
  4. Trailing zeros are significant only if the measurement is expressed in scientific notation: Trailing zeros are only considered significant if the measurement is expressed in scientific notation.

Conclusion

In conclusion, the SI system is a widely accepted system of measurement that provides a standardized way of expressing physical quantities. It consists of seven fundamental units and two supplementary units, which are used to express various physical quantities. The SI system has several advantages, including universal acceptance, consistency, precision, and flexibility. Significant figures are used to express the precision of a measurement and to indicate the level of uncertainty associated with it. By following the rules for counting significant figures, we can ensure that our measurements are accurate and reliable.
Frequently Asked Questions (FAQs) on SI Units and Significant Figures

Q1: What is the difference between a fundamental unit and a supplementary unit in the SI system?

A1: A fundamental unit is a basic unit of measurement that is used to express a physical quantity, such as length, mass, or time. A supplementary unit is a unit that is used to express a derived quantity, such as angle or solid angle.

Q2: What is the definition of a meter in the SI system?

A2: A meter is defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.

Q3: What is the difference between a kilogram and a gram?

A3: A kilogram is a unit of mass that is equal to 1,000 grams.

Q4: What is the definition of a second in the SI system?

A4: A second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

Q5: What is the difference between an ampere and a coulomb?

A5: An ampere is a unit of electric current, while a coulomb is a unit of electric charge.

Q6: What is the definition of a kelvin in the SI system?

A6: A kelvin is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.

Q7: What is the difference between a mole and a gram?

A7: A mole is a unit of amount of substance, while a gram is a unit of mass.

Q8: What is the definition of a candela in the SI system?

A8: A candela is defined as the luminous intensity of a source that emits monochromatic radiation of frequency 540 x 10^12 hertz and has a radiant intensity of 1/683 watts per steradian.

Q9: What is the difference between a radian and a degree?

A9: A radian is a unit of plane angle, while a degree is a unit of plane angle that is equal to 1/360 of a circle.

Q10: What is the definition of a steradian in the SI system?

A10: A steradian is defined as the ratio of the area of a sphere to the square of its radius.

Q11: What is the difference between significant figures and decimal places?

A11: Significant figures are the digits in a measurement that are known to be reliable and certain, while decimal places are the digits that are used to express a measurement in a specific format.

Q12: How do I determine the number of significant figures in a measurement?

A12: To determine the number of significant figures in a measurement, you can use the following rules:

  • Non-zero digits are always significant.
  • Zeros between non-zero digits are significant.
  • Leading zeros are not significant.
  • Trailing zeros are significant only if the measurement is expressed in scientific notation.

Q13: What is the difference between a precise measurement and an accurate measurement?

A13: A precise measurement is one that has a small uncertainty, while an accurate measurement is one that is close to the true value.

Q14: How do I express a measurement in scientific notation?

A14: To express a measurement in scientific notation, you can use the following format:

  • The measurement is expressed as a number between 1 and 10.
  • The number is multiplied by a power of 10, which is expressed as a small number with an exponent.

Q15: What is the importance of significant figures in scientific measurements?

A15: Significant figures are important in scientific measurements because they provide a way to express the precision and accuracy of a measurement. By following the rules for counting significant figures, you can ensure that your measurements are accurate and reliable.