Electricity -Part 1.pdf

Applied College Fundamental of ELECTRICITY Diploma Program in: 3D Printing Technology DR. Tahani Shatir 1 No List of Topics 1 Electric Current 2 Electric potential and Potential difference 3 Symbols of...

Applied College Fundamental of ELECTRICITY Diploma Program in: 3D Printing Technology DR. Tahani Shatir 1 No List of Topics 1 Electric Current 2 Electric potential and Potential difference 3 Symbols of components used in electric circuits 4 Resistance 5 DR. Tahani Shatir 2 Electric current :- is the flow of electrons through a conductor. The device which causes the flow of electrons through a conductor is called a cell. Electrons flow from the negative terminal to the positive terminal. Electric current flows from the positive terminal to the negative terminal. This is called conventional current. DR. Tahani Shatir 3  3a) Electric circuit :- Electric circuit :- is a continuous and closed path of an electric current. A schematic diagram of an electric circuit comprising of a cell, electric bulb, ammeter and plug key. bulb cell - + + A ammeter - plug key Charge is a basic SI unit, measured in Coulombs (C) Charge of single electron is 1.602*10-19 C One Coulomb is quite large, 6.24*1018 electrons. DR. Tahani Shatir 4 Electric current is expressed as :- The rate of flow of charges through a conductor or the quantity of charges flowing through a conductor in unit time. Q I = I – current t Q – quantity of charge t – time The SI unit of electric charge is coulomb (C). It is the charge contained in 6x10 18 electrons. The SI unit of current is called ampere (A). One ampere is the current flowing through a conductor if I coulomb of charge flows through it in 1 second. 1coulomb 1ampere = 1 second Electric Current is measured by an ammeter. It is always connected in series in a circuit. DR. Tahani Shatir 5 DR. Tahani Shatir 6  2) Electric potential and Potential difference :- Electric current will flow through a conductor only if there is a difference in the electric potential between the two ends of the conductor. This difference in electric potential between the two ends of a conductor is called potential difference. The potential difference in a circuit is provided by a cell or battery. The chemical reaction in the cell produces a potential difference between the two terminals and sets the electrons in motion and produces electric current. DR. Tahani Shatir 7 Potential difference :- between two points A and B of a conductor is the amount of work done to move a unit charge from A to B. Work done W Potential difference = ‫ـــــــــــــــــــ‬ or V = ‫ـــــــــ‬ Charge Q The SI unit of potential difference is volt (V). One volt is the potential difference when 1 joule of work is done to move a charge of 1 coulomb from one point to the other. 1 joule 1J 1 volt = ‫ـــــــــــ‬ or 1 V = ‫ـــــــــــــ‬ 1 coulomb 1C DR. Tahani Shatir 8  Potential difference is measured by a voltmeter. It is always connected in parallel across the two point between which the potential difference is to be measured. Charge is a basic SI unit, measured in Coulombs (C) Charge of single electron is 1.602*10-19 C One Coulomb is quite large, 6.24*1018 electrons. In the lab, one typically sees (pC, nC, or μC) Charge is always multiple of electron charge Charge cannot be created or destroyed, only transferred. DR. Tahani Shatir 9 b) Symbols of components used in electric circuits :- + - + - An electric cell A battery or combination of cells Plug key or switch Plug key or switch (open) (closed) Electric bulb A resistor of resistance R Variable resistance or or rheostat Ammeter + - Voltmeter + - A v A wire joint A wire crossing over without joining DR. Tahani Shatir 10 Symbols of some Electric components DR. Tahani Shatir 11  4) Ohm’s law :- Ohms law is a relationship between the potential difference across a conductor and the current flowing through it. Ohm’s law states that :- ‘The current flowing through a conductor is directly proportional to the potential difference between its ends provided its temperature remains constant.’ V V I α V or V α I or = constant or =R I I Where R is a constant called resistance for a given metallic wire at a given temperature. DR. Tahani Shatir 12 Verification of Ohm’s law :- Set up the circuit as shown in the circuit diagram. First use one cell and note the current (I) in the ammeter and the potential difference (V) in the voltmeter across the nichrome wire AB. Repeat by using two cells, three cells and four cells and note the readings in the ammeter and voltmeter. Then plot a graph between the current (I) and potential difference (V). + - K ( ) R A B + A - V DR. Tahani Shatir 13 + - The graph will be a straight line. This shows that the current flowing through a conductor is directly proportional to the potential difference across its ends. V I α V or V α I or ‫ = ـــــ‬R I where R is a constant called resistance of the conductor. Potential difference ( V ) Current ( I ) DR. Tahani Shatir 14  5a) Resistance :- A resistor can be used to control the amount of current flowing in a circuit. Resistance is the property of a conductor to resist the flow of current through it. V According to Ohm’s law R = ‫ــــــ‬ I The SI unit of resistance is ohm (Ω). DR. Tahani Shatir 15  If the potential difference across the two ends of a wire is 1 V and the current flowing through it is 1 A then the resistance R of the conductor is 1 ohm (1 Ω ). V Since I = ___ R The current flowing through a resistor is inversely proportional to the resistance. So if the resistance is doubled, then the current gets halved. DR. Tahani Shatir 16  b) Resistors in parallel :- R1 I1 R2 A I2 B R3 I3 V + - + - () - A + When three resistors R1, R2 and R3 are connected in parallel across AB, i) The voltage (PD) in all the resistors is the same. ii) The total current in all the resistors is the sum of the current in each resistor. I = I1 + I2 + I3 iii) The reciprocal of the equivalent resistance is the sum of the reciprocals of each resistance. 1 1 1 1 = + + Rp R1 R2 R3 DR. Tahani Shatir 17 DR. Tahani Shatir 18 6a) Resistors in series :- R1 R2 R3 A B V1 V2 V3 V + - + - ( ) - A + When three resistors R1, R2 and R3 are connected in series across AB i) The current in all the resistors is the same. ii) The total voltage (PD) across the resistors is equal to the sum of the voltage across each resistor. V = V 1 + V2 + V3 iii) The eqvivalent resistance is the sum of the resistances of each resistor. RS = R1 + R2 + R3 DR. Tahani Shatir 19 DR. Tahani Shatir 20 DR. Tahani Shatir 21 DR. Tahani Shatir 22 Exmple: Find 1- The Equivalent Resistance between a and b? 2- The Current in the circuit? 3- The Current in Each Resistence DR. Tahani Shatir 23  Example Find 1-The Equivalent Resistance between a and c? 2-The current in circuit, If the voltage between the two points is 42v 3- The Current in each Resistance I8 = I4 = I6 = DR. Tahani Shatir 24 I3 =