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Chapter 1: Units and Dimensions

SI Mechanical Units– Fundamental Units

• Length: meter (m)

• Mass: kilogram (kg)

• Time: second (s)

– Derived Units• Meter Squared (m2)

• Liter

– Unit of Force• Newton (N): the force which will give

a mass of 1 kilogram an acceleration of 1 meter per second per second.

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– Work (joule (J))• The work done in moving a body is

the product of the force and the distance through which the body is moved in the direction of the force.

• The joule is defined as the amount of work done when a force of 1 newton acts through a distance of 1 meter.

• The joule may also be termed a newton-meter.

– Energy: the capacity for doing work, joule (J)

– Power: the time rate of doing work• If a certain amount of work W is to be

done in a time t, the power required is

• The Watt is defined as the power developed when 1 joule of work is done in 1 second.

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time

WorkPower

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Scientific Notation and Metric Prefixes– Scientific Notation: very large or

very small numbers are conveniently written as a number multiplied by 10 raised to a power

– Metric Prefixes: a letter symbols for the various multiples and submultiples of 10

– Engineering Notation: Symbol, e.g., T for tera, G for giga, M for mega, and k for kilo.

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SI Electrical Units– Units of Current and Charge

• Ampere (A): the unit of electric current and is defined as that constant current which, when flowing in each of two infinitely long parallel conductors 1 meter apart, exert a force of

of length of each conductor

• Coulomb (C) is defined as that charge which passes a given point in a conductor each second, when a current of 1 ampere flows.

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– Emf, Potential Difference, and Voltage

• Volt (V): is the unit of electromotive force (emf) and potential difference.

• The volt is defined as the potential difference between two points on a conductor carrying a constant current of 1 ampere when the power dissipated between these points is 1 watt.

– Resistance and Conductance• Ohm (): is defined as that resistance

which permits a current flow of 1 ampere when a potential difference of 1 volt is applied to the resistance.

• Conductance (G): is applied to the reciprocal of resistance. The siemens (S) is the unit of conductance.

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– Magnetic Flux and Flux Density• Weber (Wb): is defined as the

magnetic flux which, linking a single-turn coil, produces an emf of 1 V when the flux is reduced to zero at a constant rate in 1 s

• Tesla (T): is the flux density in a magnetic field when 1 weber of flux occurs in a plane of 1 square meter; i.e., 1 Wb/m2

– Inductance• The inductance of a circuit is 1

henry (H) when an emf of 1 volt is induced by the current changing at the rate of 1 A/s.

– Capacitance• The farad (F): is the capacitance of a

capacitor that contain a charge of 1 coulomb when the potential difference between its terminals is 1 volt

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SI Temperature Scales– Celsius scale; has 100 equal

divisions (or degrees)– Kelvin scale (absolute scale)

• Commences at absolute zero temperature (-273.15oC)

Dimensions

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Standards– International Standards

• Defined by international agreements and maintained at the International Bureau of Weights and Measures in France

– Primary Standards• Maintained at institutions in various

countries around the world• Main function: Checking the

accuracy of secondary standards

– Secondary Standards• Employed in industry as references

for calibrating high-accuracy equipment and components and for verifying the accuracy of working standards

– Working Standards• Used as measurement references on

a day-to-day basis in all electronics lab