Electronics. Basic Concepts. Yrd. Doç. Dr. Aytaç GÖREN Yrd. Doç. Dr. Levent ÇETİN

Transcription

1 Electronics Basic Concepts

2 Electric charge Ordinary matter is made up of atoms which have positively charged nuclei and negatively charged electrons surrounding them. Charge is quantized as the subtraction of number of protons from number of electrons. (Unit: Coulombs)

3 Electric charge The influence of charges is characterized in terms of the forces between them (Coulomb's law) and the electric field and voltage produced by them. F e k e k e q 1 d q 2 2 N 1 9 Nm C 2

4 Electric Current The rate of flow of electric charge is called electric current (I) and is measured in Coulombs/second which is named Amperes. Since electric charge is quantized in discrete multiples of the electron charge, it is instructive to look at electric current as the movement of multiple microscopic charge carriers in a conductor

5 Direction of Electric Current The conventional current direction is the direction from high voltage to low voltage, high energy to low energy, and thus has some appeal in its parallel to the flow of water from high pressure to low The flow of electrons around the circuit is opposite to the direction of the conventional current flow. This is because the charge on an electron is negative by definition and so is attracted to the positive terminal.

6 Ammeter An ammeter is an instrument for measuring the electric current in amperes in a branch of an electric circuit. It must be placed in series with the measured branch, and must have very low resistance to avoid significant alteration of the current it is to measure.

7 Electrical Potential Difference or Voltage Voltage, ( V ) is the potential energy of an electrical supply stored in the form of an electrical charge. Voltage can be thought of as the force that pushes electrons through a conductor and the greater the voltage the greater is its ability to "push" the electrons through a given circuit.

8 Voltmeter A voltmeter measures the change in voltage between two points in an electric circuit and therefore must be connected in parallel with the portion of the circuit on which the measurement is made.

9 Electric Circuit Most practical applications of electricity involve the flow of electric current in a closed path under the influence of a driving voltage, analogous to the flow in a water circuit under the influence of a driving pressure. A complete path, typically through conductors such as wires and through circuit elements, is called an electric circuit.

10 Resistance The Resistance, ( R ) of a circuit or an element of the circuit is its ability to resist or prevent the flow of current (electron flow) through itself making it necessary to apply a greater voltage to the electrical circuit to cause the current to flow again. Resistance is measured in Ohms, Greek symbol ( Ω, Omega ) with prefixes used to denote Kilo-ohms (kω = 10 3 Ω) and Mega-ohms (MΩ = 10 6 Ω). Resistance cannot be negative only positive.

11 Resistivity The resistance of a given sample will increase with the length, but decrease with greater cross-sectional area. Resistance is measured in ohms. Length over area has units of 1/distance. To end up with ohms, resistivity must be in the units of "ohms distance" R L m Ωm A m 2 Electrical resistivity (also known as resistivity, specific electrical resistance, or volume resistivity) is a measure of how strongly a material opposes the flow of electric current.

12 Relationship between Voltage and Current Relationship between Voltage and Current in a circuit of constant resistance: Quantity Symbol Unit of Measure Abbreviati on Voltage V or E Volt V Current I Amp A Resistance R Ohms Ω

13 Ohmmeter The standard way to measure resistance in ohms is to supply a constant voltage to the resistance and measure the current through it. That current is of course inversely proportional to the resistance. Multimeter video

14 Alternating or Direct The source of an electric circuit may be an Alternating or Direct current or voltage supply. In alternating current (AC, also ac), the movement of electric charge periodically reverses direction. In direct current (DC, also dc), the flow of electric charge is only in one direction.

15 Alternating Current or Voltage AC is the form in which electric power is delivered to businesses and residences. The usual waveform of an AC power circuit is a sine wave.

16 The AC Waveform

17 The AC Waveform There are 3 ways to quantify the magnitude of a sine wave. Peak voltage determines how far the voltage swings, either positive or negative, from the point of reference. Peak-Peak Voltage represents how far the voltage swings, from positive to negative max values. The RMS Voltage represents the effective voltage in an AC system. The RMS values of AC voltages are the DC equivalent values that provide the same power to the load. For sinusoidal network voltage: V V max RMS. 707 V max 2 0

18 Measurement of AC Waveform An instrument called an oscilloscope is used to display a changing voltage over time on a graphical screen. Oscilloscope video

19 Osciloscope

20 Osciloscope

21 Resistance in AC Circuits The circuits elements, under the effect of AC sources, demonstrate a complex oppositon effect against the electron flow. This oppositon is called impedance. The impedance is used to describe voltage current relationship in AC circuits.

22 Power in Electric Circuits The electric power in watts associated with a complete electric circuit or a circuit component represents the rate at which energy is converted from the electrical energy of the moving charges to some other form, e.g., heat, mechanical energy, or energy stored in electric fields or magnetic fields. In a DC Circuit the power is given by the product of applied voltage and the electric current: P = VI [Watt]

23 Power in Electric Circuits As in DC circuits, the instantaneous electric power in an AC circuit is given by P=VI where V and I are the instantaneous voltage and current.

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25 References - Hyperphysics website. -