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Measurements and Units
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• Each physical quantities is measured in its own units, by comparison with a standard.
• A unit is unique name assigned to measure of that quantity. , for example, meter for the quantity length.
• All physical quantities can be divided into two groups – dependent and independent.
• Independent physical quantities are measured in terms of base standards or units.
The SI System of Unit
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SI – Systéme International
International system of measurement
Developed in 1960 from the MKS (meter-kilogram-second) system
World’s most widely used system of measurement
A unified system of measurements : MKS (meter-kilogram-second)Electrical, magnetic quantities
Modified and created through international agreement (For example, the ‘meter’ is now defined as the distance travelled by light in a vacuum in 1/299,792,458 of second, but initially it was defined as one ten-millionth of the distance from the north pole to the equator)
Standards
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Standard kg at NIST Atomic Clock at NISTAccuracy of about 3 millionth of a second
Types of Units
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• Length - meter (m)
• Mass - kilogram (kg)
• Time - second (s)
• Temperature - kelvin (K)
Base Units:
Derived Units:
• Force – newton (N)• Energy – joule (J)• Frequency – Hertz (Hz) and so on…..
Relative Size of Units
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• 1 meter is about 1 yard.
• 1 inch is about 2½ centimeters.
• 1 newton is about the force required to lift a ¼-pound weight.
• Raising a ¼-pound weight 1 meter in 1 s requires about 1 watt.
Converting Units
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• Convert 60 miles/hour to km/hr.
• Convert 60 miles/hour to m/s
• A circle has radius of 8 inches. Determine the area in square meters
• A car travels 60ft in 2 seconds. Determine
a. its speed in meter per second
b. its speed in kilometer per hour
Power of Ten Notation
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• Used to handle very large and very small numbers
• 35 000 = 3.5 × 104 or 35 × 103
• 458 000 = 4.58 × 105 or 458 × 103
• 0.000 042 = 4.2 × 10-5 or 42 × 10-6
Types of Notations
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• Scientific Notation - Power of ten numbers are written with one digit to the left of the
decimal place
24 700 = 2.4 × 104
0.000 046 = 4.6 × 10-5
• Engineering Notation - uses only powers which are factors of 3:
24 700 = 24.7 × 103
0.000 046 = 46 × 10-6
Engineering Notations
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Engineering Notations
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• Convert 0.01MV to kiloVolts
• Convert 35cm to nm
• Compute the sum of 1A and 100mA
• If I1= 120 mA and I2= 234×10-3A, what is I1 + I2 in mA?
Density
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• Density is defined as mass per unit volume, measured in kg/m3
• Atomic mass of an element is defined as the average mass of an atom, measured in u (1 u = 1.66053886x10-27kg)
• One mole (mol) of a substance is that amount of the substance that contains as many particles(atoms, molecules, or other particles) as there are atoms in 12 g of the carbon-12 isotope. Onemole of substance A contains the same number of particles as there are in 1 mol of any othersubstance B.
• One mole of a substance contains 6.023x1023 atoms.
Example 1.1
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Molar mass of aluminium is 27gm
Dimensional Analysis
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• Dimensional analysis makes use of the fact that dimensions can be treated as algebraic quantities.
• In this analysis, quantities can be added and subtracted only if they have same dimension.
Significant Digits
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• The number of digits in a number that carry actual information are calledSignificant Digits.
• It is a common error to show more digits of accuracy than are warranted.
• The number of significant digits in a result due to multiplication or division isthe same as the number of significant digits in the number with the leastnumber of significant digits.
Example 1.8
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Estimation and Order of Magnitude Calculation
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By making estimates and Order of magnitude calculation, it is possible to approximate the answer of a problem when there is not enough information available to completely specify an exact solution.
