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# Si And Cgs Units Of All Physical Quantities Pdf

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To explain the natural phenomena we take the help of physics. Physics enable us to understand logically as well as mathematically all natural phenomena. All the laws of physics are generally expressed in terms of Physical Quantities. As an example, if you go to school or college from your home by walk, you need to know your speed and time.

## The International System of Units (SI), Physical Quantities, and Their Dimensions

Physicists, like other scientists, make observations and ask basic questions. For example, how big is an object? How much mass does it have? How far did it travel? To answer these questions, they make measurements with various instruments e. The measurements of physical quantities are expressed in terms of units, which are standardized values. For example, the length of a race, which is a physical quantity, can be expressed in meters for sprinters or kilometers for long distance runners.

Without standardized units, it would be extremely difficult for scientists to express and compare measured values in a meaningful way Figure 1. All physical quantities in the International System of Units SI are expressed in terms of combinations of seven fundamental physical units, which are units for: length, mass, time, electric current, temperature, amount of a substance, and luminous intensity.

English units were historically used in nations once ruled by the British Empire. Today, the United States is the only country that still uses English units extensively.

Virtually every other country in the world now uses the metric system, which is the standard system agreed upon by scientists and mathematicians. Some physical quantities are more fundamental than others. In physics, there are seven fundamental physical quantities that are measured in base or physical fundamental units: length, mass, time, electric current temperature, amount of substance, and luminous intensity. Units for other physical quantities such as force, speed, and electric charge described by mathematically combining these seven base units.

In this course, we will mainly use five of these: length, mass, time, electric current and temperature. The units in which they are measured are the meter, kilogram, second, ampere, kelvin, mole, and candela Table 1. All other units are made by mathematically combining the fundamental units. These are called derived units. The SI unit for length is the meter m. The definition of the meter has changed over time to become more accurate and precise.

This measurement was improved in by redefining the meter to be the distance between two engraved lines on a platinum-iridium bar. By , some distances could be measured more precisely by comparing them to wavelengths of light. The meter was redefined as 1,, The SI unit for mass is the kilogram kg.

It is defined to be the mass of a platinum-iridium cylinder, housed at the International Bureau of Weights and Measures near Paris. Exact replicas of the standard kilogram cylinder are kept in numerous locations throughout the world, such as the National Institute of Standards and Technology in Gaithersburg, Maryland.

The determination of all other masses can be done by comparing them with one of these standard kilograms.

The SI unit for time, the second s also has a long history. Accuracy in the fundamental units is essential, since all other measurements are derived from them. Therefore, a new standard was adopted to define the second in terms of a non-varying, or constant, physical phenomenon.

One constant phenomenon is the very steady vibration of Cesium atoms, which can be observed and counted. This vibration forms the basis of the cesium atomic clock. In , the second was redefined as the time required for 9,,, Cesium atom vibrations Figure 1. Electric current is measured in the ampere A , named after Andre Ampere. You have probably heard of amperes, or amps , when people discuss electrical currents or electrical devices.

Understanding an ampere requires a basic understanding of electricity and magnetism, something that will be explored in depth in later chapters of this book. Basically, two parallel wires with an electric current running through them will produce an attractive force on each other. One ampere is defined as the amount of electric current that will produce an attractive force of 2. The SI unit of temperature is the kelvin or kelvins, but not degrees kelvin.

This scale is named after physicist William Thomson, Lord Kelvin, who was the first to call for an absolute temperature scale.

The Kelvin scale is based on absolute zero. This is the point at which all thermal energy has been removed from all atoms or molecules in a system. Conveniently, the Kelvin scale actually changes in the same way as the Celsius scale. Physical objects or phenomena may vary widely. For example, the size of objects varies from something very small like an atom to something very large like a star. Yet the standard metric unit of length is the meter.

So, the metric system includes many prefixes that can be attached to a unit. Each prefix is based on factors of 10 10, , 1,, etc. Table 1. See Appendix A for a discussion of powers of The metric system is convenient because conversions between metric units can be done simply by moving the decimal place of a number. This is because the metric prefixes are sequential powers of There are centimeters in a meter, meters in a kilometer, and so on.

In nonmetric systems, such as U. Another advantage of the metric system is that the same unit can be used over extremely large ranges of values simply by switching to the most-appropriate metric prefix. For example, distances in meters are suitable for building construction, but kilometers are used to describe road construction.

Therefore, with the metric system, there is no need to invent new units when measuring very small or very large objects—you just have to move the decimal point and use the appropriate prefix. You can see that scientists use a range of measurement units.

This wide range demonstrates the vastness and complexity of the universe, as well as the breadth of phenomena physicists study. As you examine this table, note how the metric system allows us to discuss and compare an enormous range of phenomena, using one system of measurement Figure 1.

Scientific notation is a way of writing numbers that are too large or small to be conveniently written as a decimal. For example, consider the number ,,,, The scientific notation for this number is 8. Scientific notation follows this general format. In this format x is the value of the measurement with all placeholder zeros removed.

In the example above, x is 8. The x is multiplied by a factor, 10 y , which indicates the number of placeholder zeros in the measurement.

Placeholder zeros are those at the end of a number that is 10 or greater, and at the beginning of a decimal number that is less than 1. In the example above, the factor is 10 This tells you that you should move the decimal point 14 positions to the right, filling in placeholder zeros as you go. In this case, moving the decimal point 14 places creates only 13 placeholder zeros, indicating that the actual measurement value is ,,,, Numbers that are fractions can be indicated by scientific notation as well.

Consider the number 0. Its scientific notation is 4. Its scientific notation has the same format. Here, x is 4. However, the value of y in the 10 y factor is negative, which indicates that the measurement is a fraction of 1. Therefore, we move the decimal place to the left, for a negative y. In our example of 4. The term order of magnitude refers to the power of 10 when numbers are expressed in scientific notation.

Quantities that have the same power of 10 when expressed in scientific notation, or come close to it, are said to be of the same order of magnitude. Both numbers have the same value for y. Therefore, and are of the same order of magnitude. Similarly, and 99 would be regarded as the same order of magnitude, 10 2. Order of magnitude can be thought of as a ballpark estimate for the scale of a value. These two values are 18 orders of magnitude apart.

Scientists make frequent use of scientific notation because of the vast range of physical measurements possible in the universe, such as the distance from Earth to the moon Figure 1. It is often necessary to convert from one type of unit to another. For example, if you are reading a European cookbook in the United States, some quantities may be expressed in liters and you need to convert them to cups. A Canadian tourist driving through the United States might want to convert miles to kilometers, to have a sense of how far away his next destination is.

How can we want to convert 1 hour to seconds? Next, we need to determine a conversion factor relating meters to kilometers. A conversion factor is a ratio expressing how many of one unit are equal to another unit.

A conversion factor is simply a fraction which equals 1. You can multiply any number by 1 and get the same value. When you multiply a number by a conversion factor, you are simply multiplying it by one. In this case, we know that there are 1, meters in 1 kilometer. Now we can set up our unit conversion.

## List of physical quantities

Physicists, like other scientists, make observations and ask basic questions. For example, how big is an object? How much mass does it have? How far did it travel? To answer these questions, they make measurements with various instruments e. The measurements of physical quantities are expressed in terms of units, which are standardized values. For example, the length of a race, which is a physical quantity, can be expressed in meters for sprinters or kilometers for long distance runners.

## Physical Quantities Measurements Standards & Units > Important Physics GK [PDF]

The seven units along with their SI unit and symbol are. It also handles logarithmic units such as magnitude and decibel. English: Metrological dependencies between the different base units of the SI system of units as agreed to on 16 November All physical quantities can be expressed in terms of seven fundamental base quantities such as mass, length, time, temperature, electric current, luminous intensity and amount of substance. These units are used in combination to define additional units for other important physical quantities such as force and energy.

This is a list of physical quantities. The first table lists the base quantities used in the International System of Units to define the physical dimension of physical quantities for dimensional analysis. The second table lists the derived physical quantities. Derived quantities can be mentioned in terms of the base quantities.

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#### Physical Quantities

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Enmomaho1950 27.03.2021 at 04:22

MKS: N/ m2 or (kg × m/s2)/m2. (Pascal). CGS: dyne/cm2 work. (force times distance over which the force is applied to an object as the object moves under the.

Tatiana V. 27.03.2021 at 05:14

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Daisy P. 31.03.2021 at 03:36

APPENDIX PHYSICAL QUANTITIES AND THEIR SI UNITS symbol. SI measurement units symbol unit dimensions distance d meter m m mass m kilogram kg.