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Chapter 1: Units and Dimensions

Chapter 1: Units and Dimensions. SI Mechanical Units Fundamental Units Length: meter ( m ) Mass: kilogram ( kg ) Time: second ( s ) Derived Units Meter Squared ( m 2 ) Liter Unit of Force

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Chapter 1: Units and Dimensions

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  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. SI Temperature Scales • Celsius scale; has 100 equal divisions (or degrees) • Kelvin scale (absolute scale) • Commences at absolute zero temperature (-273.15oC) • Dimensions

  8. 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

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